PDF - CES (IISc)

Cambridge Botanical Handbooks 

Edited by A. C. SEWARD and A. G. TANSLEY 

LICHENS

CAMBRIDGE UNIVERSITY PRESS 

LONDON : 

C. F. CLAY, MANAGER 

FETTER 

LANE, E.C. 4 

LONDON : H. K. LEWIS AND CO., LTD., 

136, Gower Street, W.C. i 

LONDON : WHELDON & WESLEY, LTD., 

28, Essex Street, Strand, W.C. 2 

NEW YORK : 

THE 

MACMILLAN CO. 

BOMBAY 

~| 

CALCUTTA I MACMILLAN AND CO., LTD. 

MADRAS J 

TORONTO : THE MACMILLAN CO. OF 

TOKYO : 

CANADA, LTD. 

MARUZEN-KABUSHIKI-KAISHA 

ALL RIGHTS RESERVED

LICHENS 

BY 

ANNIE LORRAIN SMITH, F.L.S. 

ACTING ASSISTANT, BOTANICAL DEPARTMENT, BRITISH MUSEUM 

CAMBRIDGE: 

AT THE UNIVERSITY PRESS 

1921 

r r t\ ~J i JuUl 1

IN RBAT MfTAUE.

PREFACE 

THE publication of this volume has been delayed owing to war conditions, 

but the delay is the less to be regretted in that it has allowed 

the inclusion of recent work on the subject. Much of the subject-matter 

is of common knowledge to lichenologists, but in the co-ordination and 

arrangement of the facts the original papers are cited throughout. The 

method has somewhat burdened the pages with citations, but it is hoped 

that, as a book of reference, its value has been enhanced thereby. The 

Glossary includes terms used in lichenology, or those with a special licheno- 

logical meaning. The Bibliography refers only to works consulted in the 

preparation of this volume. To save space, etc., the titles of books and papers 

quoted in the text are generally translated and curtailed: full citations-will 

be found in the Bibliography. Subject-matter has been omitted from the 

index : references of importance will be found in the Table of Contents or 

in the Glossary. 

I would record my thanks to those who have generously helped me 

during the preparation : 

I O 

of the volume to Lady Muriel Percy for taking 

notes of spore production, and to Dr Cavers for the loan of reprints. Prof. 

Potter and Dr Somerville Hastings placed at my disposal their photographs 

of the living plants. Free use has been made of published text-figures 

which are duly acknowledged. 

I have throughout had the inestimable advantage of being able to consult 

freely the library and herbarium of the British Museum, and have thus been 

able to verify references to plants as well as to literature. A special debt 

of gratitude is due to my colleagues Mr Gepp and Mr Ramsbottom for 

their unfailing assistance and advice. 

LONDON, 

February) 1920 

A. L. S.

CONTENTS 

PAGE 

GLOSSARY xix 

ERRATA xxii 

INTRODUCTION xxiii 

CHAPTER I 

HISTORY OF LICHENOLOGY 

A. INTRODUCTORY i 

B. PERIOD I. PREVIOUS TO 1694 2 

C. PERIOD II. 16941729 5 

D. PERIOD III. 1729 1780 6 

E. PERIOD IV. 17801803 ...... 9 

F. PERIOD V. 18031846 ...... 10 

G. PERIOD VI. 18461867 . 

H. PERIOD VII. 

'. 

1867 AND AFTER 

^15 

'18 

CHAPTER II 

CONSTITUENTS OF THE LICHEN THALLUS 

I. LICHEN GONIDIA 

i. GONIDIA IN RELATION TO THE THALLUS 

A. HISTORICAL ACCOUNT OF LICHEN GONIDIA . . 21 

B. GONIDIA CONTRASTED WITH ALGAE 22 

C. CULTUREEXPERIMENTSWITHTHELlCHENTHALLUS 24 

D. THEORIES AS TO THE ORIGIN OF GONIDIA . . 25 

E. MICROGONIDIA 26 

F. COMPOSITE NATURE OF THALLUS .... 27 

G. SYNTHETIC CULTURES 27 

H. HYMENIAL GONIDIA 30 

I. NATURE OF ASSOCIATION BETWEEN ALGA AND 

FUNGUS 31 

a. Consortium and symbiosis 

b. Different forms of association 

J. RECENT VIEWS ON SYMBIOSIS AND PARASITISM . 36 

2. PHYSIOLOGY OF THE SYMBIONTS 

A. NUTRITION OF LICHEN ALGAE 39 

a. Character of algal cells 

b. Supply of nitrogen 

c. Effect on the alga 

d. Supply of carbon 

e. Nutrition within the symbiotic plant 

/ Affinities of lichen gonidia 

B. NUTRITION OF LICHEN FUNGI 44 

C. SYMBIOSIS OF OTHER PLANTS . . . . . 45

viii CONTENTS 

II. LICHEN HYPHAE 

PAGE 

A. ORIGIN OF HYPHAE . 46 

B. DEVELOPMENT OF LICHENOID HYPHAE . . . 47 

C. CULTURE OF HYPHAE WITHOUT GONIDIA . . 49 

D. CONTINUITY OF PROTOPLASM IN HYPHAL CKLLS . 51 

III. LICHEN ALGAE 

A. TYPES OF ALGAE 51 

a. Myxophyceae associated with Phycolichens 

b. Chlorophyceae associated with Archilichens 

B. CHANGES INDUCED IN THE ALGA .... 60 

a. Myxophyceae 

b. Chlorophyceae 

C. CONSTANCY OF ALGAL CONSTITUENTS ... 63 

D. DISPLACEMENT OF ALGAE WITHIN THE THALLUS . 64 

a. Normal displacement 

b. Local displacement 

E. NON-GONIDIAL ORGANISMS ASSOCIATED WITH 

LICHEN HYPHAE . . ... . . . 65 

F. PARASITISM OF ALGAE ON LICHENS . . , . 65 

I. 

CHAPTER III 

MORPHOLOGY 

GENERAL ACCOUNT OF LICHEN STRUCTURE 

ORIGIN OF LICHEN STRUCTURES 

A. 

B. 

FORMS OF CELL-STRUCTURE 

TYPES OF THALLUS . . 

. 

. 

. 

\ ,. 

'.' 

. 

. 

. 

67 

68 

a. Endogenous thallus 

b. Exogenous thallus 

II. STRATOSE THALLUS 

i. CRUSTACEOUS LICHENS 

A. GENERAL STRUCTURE . ... .. 

- 

B. SAXICOLOUS LICHENS . . . 

- 

.. > 

a. Epilithic lichens 

aa. Hypothallus or protothallus 

bb. Formation of crustaceous tissues 

cc. Formation of areolae 

b. Endolithic lichens 

c. Chemical nature of the substratum 

C. CORTICOLOUS LICHENS 

a. Epiphloeodal lichens 

b. Hypophloeodal lichens 

-..', . 70 

. ;

CONTENTS ix 

2. SQUAMULOSE LICHENS 

I'AGE 

A. DEVELOPMENT OF THE SQUAMULE .... 79 

B. TISSUES OF SQUAMULOSE THALLUS . . . . 81 

3. 

FOLIOSE LICHENS 

A. DEVELOPMENT OF FOLIOSE THALLUS ... 82 

B. CORTICAL TISSUES 82 

a. Types of cortical structure 

b. Origin of variation in cortical structure 

c. Loss and renewal of cortex 

d. Cortical hairs 

C. GONIDIAL TISSUES . . . . . . . 87 

D. MEDULLA AND LOWER CORTEX .... 88 

a. Medulla 

b. Lower cortex 

c. Hypothallic structures 

E. STRUCTURES FOR PROTECTION AND ATTACHMENT . 91 

a. Cilia 

b. Rhizinae 

c. Haptera 

F. STRENGTHENING TISSUES OF STRATOSE LICHENS . 

a. Produced by development of cortex 

b. Produced by development of veins or nerves 

III. RADIATE THALLUS 

1. CHARACTERS OF RADIATE THALLUS 

2. INTERMEDIATE TYPES OF THALLUS 

3. 

FRUTICOSE AND FILAMENTOUS THALLUS 

95 

A. GENERAL STRUCTURE OF THALLUS 101 

Cortical Structures 

a. The fastigiate cortex 

b. The fibrous cortex 

B. SPECIAL STRENGTHENING STRUCTURES . 

a. Sclerotic strands 

/'. Chondroid axis 

. .103 

C. SURVEY OF MECHANICAL TISSUES .... 105 

D. RETICULATE FRONDS 106 

E. ROOTING BASE IN FRUTICOSE LICHENS . . . 108 

IV. STRATOSE-RADIATE THALLUS 

i. STRATOSE OR PRIMARY THALLUS 

A. GENERAL CHARACTERISTICS HI 

B. TISSUES OF PRIMARY THALLUS 112 

a. Cortical tissue 

b. Gonidial tissue 

c. Medullary tissue 

d. Soredia

x CONTENTS 

2. RADIATE OR SECONDARY THALLUS 

PAGE 

A. ORIGIN OF THE PODETIUM . . . .114 

B STRUCTURE OF THE PODETIUM . . . .114 

a. General structure 

b. Gonidial tissue 

c. Cortical tissue 

d. Sored ia 

C. DEVELOPMENT OF THE SCYPHUS . 

. . .117 

a. From abortive apothecia 

b. From polytomous branching 

c. From arrested growth 

d. Gonidia of the scyphus 

e. Species without scyphi 

D. BRANCHING OF THE PODETIUM . . . . 119 

E. PERFORATIONS AND RETICULATION OF THE PODE- 

F. 

TIUM 

ROOTING STRUCTURES OF CLADONIAE . . 

120 

.121 

G. HAPTERA 122 

H. MORPHOLOGY OF THE PODETIUM . 

I. PILOPHORUS AND STEREOCAULON . 

. . .122 

. . .125 

V. STRUCTURES PECULIAR TO LICHENS 

i. AERATION STRUCTURES 

A. CYPHELLAE AND PSEUDOCYPHELLAE . 

a. Historical 

b. Development of cyphellae 

c. Pseudocyphellae 

d. Occurrence and distribution 

. .126 

B. BREATHING-PORES 129 

a. Definite breathing-pores 

b. Other openings in the thallus 

C. GENERAL AERATION OF THE THALLUS . 

2. CEPHALODIA 

. .132 

A. HISTORICAL AND DESCRIPTIVE 133 

B. CLASSIFICATION 135 

I. CEPHALODIA VERA 

II. PSEUDOCEPHALODIA 

C. ALGAE THAT FORM CEPHALODIA . . . .136 

D. DEVELOPMENT OF CEPHALODIA . . . 137 

a. Ectotrophic 

b. Endotrophic 

c. Pseudocephalodia 

E. AUTOSYMBIOTIC CEPHALODIA 140

CONTENTS xi 

3. SOREDIA 

A. STRUCTURE AND ORIGIN OF SOREDIA . . 

PAGE 

.141 

a. Scattered soredia 

b. Isidial soredia 

c. Soredia as buds 

B. SORALIA 144 

xii CONTENTS 

2. PYRENOLICHENS 

a. Development of the perithecium 

b. Formation of carpogonia 

PAGE 

D. APOGAMOUS REPRODUCTION 174 

E. DISCUSSION OF LICHEN REPRODUCTION . . . 177 

a. The Trichogyne 

b. The Ascogonium 

F. FINAL STAGES OF APOTHECIAL DEVELOPMENT . 181 

a. Open or closed apothecia 

b. Emergence of ascocarp 

G. LICHEN ASCI AND SPORES 184 

a. Historical 

b. Development of the ascus 

c. Development of the spores 

d. Spore germination 

e. Multinucleate spores 

/ Polaribilocular spores 

II. SECONDARY SPORES 

A. REPRODUCTION BY OIDIA 189 

B. REPRODUCTION BY CONIDIA 190 

a. Rare instances of conidial formation 

b. Comparison with Hyphomycetes 

C. CAMPYLIDIUM AND ORTHIDIUM .... 191 

III. SPERMOGONIA OR PYCNIDIA 

A. HISTORICAL ACCOUNT OF SPERMOGONIA. . 

. 192 

B. SPERMOGONIA AS MALE ORGANS .... 193 

C. OCCURRENCE AND DISTRIBUTION .... 193 

a. Relation to thallus and apothecia 

b. Form and size 

c. Colour 

D. STRUCTURE 196 

a. Origin and growth 

b. Form and types of spermatiophores 

c. Periphyses and sterile filaments 

E. SPERMATIA OR PYCNIDIOSPORES .... 201 

a. Origin and form 

b. Size and structure 

c. Germination 

d. Variation in pycnidia 

F. PYCNIDIA WITH MACROSPORES 204

CONTENTS 

G. GENERAL SURVEY ..... . 

xiif 

PAGE 

205 

a. Sexual or asexual 

b. Comparison with fungi 

' 

c. Influence of symbiosis 

d. Value in diagnosis 

CHAPTER V 

PHYSIOLOGY 

I. CELLS AND CELL PRODUCTS 

A. CELL-MEMBRANES 209 

a. Chitin 

b. Lichenin and allied carbohydrates 

c. Cellulose 

B. CONTENTS AND PRODUCTS OF THE FUNGAL CELLS. 213 

a. Cell-substances 

b. Calcium oxalate 

c. Importance of calcium oxalate 

C. OIL-CELLS 215 

a. Oil-cells of endolithic lichens 

b. Oil-cells of epilithic lichens 

c. Significance of oil-formation 

D. LICHEN-ACIDS 221 

a. Historical 

b. Occurrence and examination of acids 

c. Character of acids 

d. Causes of variation in quantity and quality 

e. Distribution of acids 

E. CHEMICAL GROUPING OF ACIDS 225 

I. ACIDS OF THE FAT SERIES 

II. ACIDS OF THE BENZOLE SERIES 

SUBSERIES I. ORCINE DERIVATIVES 

SUBSERIES II. ANTHRACENE DERIVATIVES 

F. CHEMICAL REAGENTS AS TESTS FOR LICHENS . 228 

G. CHEMICAL REACTIONS IN NATURE .... 229 

II. GENERAL NUTRITION 

A. ABSORPTION OF WATER 229 

a. Gelatinous lichens 

b. Crustaceous lichens 

c. Foliose lichens 

d. Fruticose lichens 

B. STORAGE OF WATER 232 

b

xiv CONTENTS 

C. SUPPLY OF INORGANIC FOOD . 

a. In foliose and fruticose lichens 

b. In crustaceous lichens 

D. SUPPLY OF ORGANIC FOOD . 

a. From the substratum 

b. From other lichens 

c. From other vegetation 

. . 

... 

.... 

PAGE 

. 232 

- 

'. . . 235 

III. ASSIMILATION AND RESPIRATION 

A. INFLUENCE OF TEMPERATURE ., 

.. . . . 238 

a. 

b. 

High temperature 

Low temperature 

B. INFLUENCE OF MOISTURE . . . . . . 239 

a. On vital functions 

b. On general development 

IV. ILLUMINATION OF LICHENS 

A. EFFECT OF LIGHT ON THE THALLUS . 

a. Sun lichens 

b. Colour-changes due to light 

c. Shade lichens 

d. Varying shade conditions 

B. EFFECT OF LIGHT ON REPRODUCTIVE ORGANS . 

. . 240 

a. Position and orientation of fruits with regard to light 

b. Influence of light on colour of fruits 

V. COLOUR OF LICHENS 

244 

A. ORIGIN OF LICHEN-COLOURING . V.' . 245 

a. Colour given by the algal constituent 

A Colour due to lichen-acids 

c. Colour due to amorphous substances 

d. Enumeration of amorphous pigments 

e. Colour due to infiltration 

CHAPTER VI 

BIONOMICS 

A. GROWTH AND DURATION OF LICHENS . . .252 

B. SEASON OF FRUIT FORMATION. . .255 

C. DISPERSAL AND INCREASE 256 

a. Dispersal of crustaceous lichens 

b. Dispersal of foliose lichens 

i. Dispersal of fruticose lichens 

D. ERRATIC LICHENS . . . ... 

. 

. 

, 258

CONTENTS xv 

PAGE 

E. PARASITISM 260 

a. General statement 

b. Antagonistic symbiosis 

c. Parasymbiosis 

F. 

d. Parasymbiosis of fungi 

e. Fungi parasitic on lichens 

/ Mycetozoa parasitic on lichens 

DISEASES OF LICHENS 268 

a. 

b. 

Caused by parasitism 

Caused by crowding 

c. Caused by adverse conditions 

G. HARMFUL EFFECT OF LICHENS .... 269 

H. GALL-FORMATION 270 

A. ORIGIN OF LICHENS . 

CHAPTER VII 

PHYLOGENY 

I. GENERAL STATEMENT 

272 

B. ALGAL ANCESTORS ....... 273 

C. FUNGAL ANCESTORS 273 

a. Basidiolichens 

b. Ascolichens 

II. THE REPRODUCTIVE ORGANS 

A. THEORIES OF DESCENT IN ASCOLICHENS . 

. 273 

B. RELATION OF LICHENS TO FUNGI .... 275 

a. Pyrenocarpineae 

b. Coniocarpineae 

c. Graphidineae 

d. Cyclocarpineae 

III. THE THALLUS 

A. GENERAL OUTLINE OF DEVELOPMENT OF THALLUS 281 

a. Preliminary considerations 

b. Course of evolution in Hymenolichens 

c. Course of evolution in Ascolichens 

B. COMPARATIVE ANTIQUITY OF ALGAL SYMBIONTS . 

282 

C. EVOLUTION OF PHYCOLICHENS 283 

a. Gioeolichens 

b. Ephebaceae and Collemaceae 

c. 

d. 

e. 

Pyremdiaceae 

Heppiaceae and Pannariaceae 

Peltigeraceae and Stictaceae

xvi 

CONTENTS 

PAGE 

D. EVOLUTION OF ARCHILICHENS . . . . 287 

a. Thallus of Pyrenocarpineae 

b. Thallus of Coniocarpineae 

c. Thallus of Graphidineae 

d. Thallus of Cyclocarpineae 

AA. LECIDEALES 

aa. COENOGONIACEAE 

bb. LECIDEACEAE AND GYROPHORACEAE 

cc. CI.ADONIACEAE 

i. Origin of Cladonia 

i. Evolution of the primary thnllus 

3. Evolution of the secondary thallus 

4. Course of podetial development 

5. Variation in Cladonia 

6. Causes of variation, 

7. Podetial development and spore-dissemination 

8. Pilophorus, Stereocaulon and Argopsis 

BB. LECANORALES 

aa. COURSE OF DEVELOPMENT 

bb. LECANORACEAE 

cc, PARMELIACEAE 

dd. USNEACEAE 

ee. PHYSCIACEAE 

CHAPTER VIII 

SYSTEMATIC 

I. CLASSIFICATION 

A. WORK OF SUCCESSIVE SYSTEMATISTS . . . 304 

a. Dillenius and Linnaeus 

b. Acharius 

c. Schaerer 

d. Massalongo and Koerber 

e. Nylander 

/ M tiller-Argau g. Reinke 

h. Zahlbruckner 

B. FAMILIES AND GENERA OF ASCOLICHENS . 

. 311 

C HYMENOLICHENS 342 

II. NUMBER AND DISTRIBUTION 

i. ESTIMATES OF NUMBER 

2. GEOGRAPHICAL DISTRIBUTION 

A. GENERAL SURVEY 343 

B. LICHENS OF POLAR REGIONS 345 

C. LICHENS OF THE TEMPERATE ZONES . . .348 

D. LICHENS OF TROPICAL REGIONS .... 352 

III. FOSSIL LICHENS

CONTENTS xvii 

CHAPTER IX 

ECOLOGY 

PAGE 

A. GENERAL INTRODUCTION .* 356 

B. EXTERNAL INFLUENCES . . . 

" 

. . . 357 

a. Temperature 

b. 

c. 

d. 

Humidity 

Wind 

Human Agency 

C. LICHEN COMMUNITIES 362 

1. ARBOREAL 363 

a. Epiphyllous 

b. Corticolous 

c. Lignicolous 

2. TERRICOLOUS 367 

a. On calcareous soil 

b. On siliceous soil 

c. On bricks 

d. On humus 

e. On peaty soil 

/ On mosses 

g. On fungi 

3. SAXICOLOUS 371 

a. Characters of mineral substrata 

b. Colonization on rocks 

c. Calcicolous 

4 . OMNICOLOUS 

d. Silicicolous 

LICHENS 376 

5. LOCALIZED COMMUNITIES 378 

a. Maritime lichens 

b. Sand-dune lichens 

c. Mountain lichens 

d. Tundra lichens 

e. Desert lichens 

f. Aquatic lichens 

D. LICHENS AS PIONEERS . 

a. Soil-formers 

b. Outposts of vegetation 

.... 

CHAPTER X 

ECONOMIC AND TECHNICAL 

392 

A. LICHENS AS FOOD 395 

a. Food for insects 

b. Insect mimicry of lichens 

c. Food for the higher animals 

d. Food for man

CONTENTS 

B. LICHENS AS MEDICINE ...... 45 

a. Ancient remedies 

b. Doctrine of "signatures" 

c. Cure for hydrophobia 

d. Popular remedies 

C. LICHENS AS POISONS ..... . . 410 

D. LICHENS USED IN TANNING, BREWING AND DISTIL- 

LING ....... . . .411 

E. DYEING PROPERTIES OF LICHENS . . . .411 

a. Lichens as dye-plants 

b. The orchil lichen, Roccella 

c. Purple dyes : orchil, cudbear and litmus 

d. Other orchil lichens 

e. Preparation of orchil 

f. Brown and yellow dyes 

g. Collecting of dye-lichens 

h. Lichen colours and spectrum characters 

F. LICHENS IN PERFUMERY ...... 418 

a. Lichens as perfumes 

b. Lichens as hair-powder 

G. SOME MINOR USES OF LICHENS .... 420 

APPENDIX ....... .- . 421 

ADDENDUM ...... , 422 

BIBLIOGRAPHY . . . ... 

INDEX . 

. . . . . ... 

... 423 

448

GLOSSARY 

Acrogenous, borne at the tips of hyphae; see spermatium, 312. 

Allelositismus, Norman's term to describ* the thallus of Moriolaceae (mutualism), 313. 

Amorphous cortex, formed of indistinct hyphae with thickened walls ; cf. decomposed 

cortex. 

Amphithecium, thalline margin of the apothecium, 157. 

Antagonistic symbiosis, hurtful parasitism of one lichen on another, 261 et seq. 

Apothecium, open or disc-shaped fructification, 11, 156 et passim. Veiled apothecium, 

169. Closed or open at first, 182. 

Archilichens, lichens in which the gonidia are bright green (Chlorophyceae), 52, 55 

et passim. 

Ardella, the small spot-like apothecium of Arthoniaceae, 158. 

Areola (areolate), small space marked out by lines or chinks on the surface of the thallus, 

73 et passim. 

Arthrosterigma, septate tissue-like sterigma (spermatiophore), 197. 

Ascogonium, the cell or cells that produce ascogenous hyphae, 180 et seq. 

Ascolichens, lichens in which the fungus is an Ascomycete, 159, 173 et passim. 

Ascus, enlarged cell in which a definite number of spores (usually 8) are developed ; cf. 

theca, 157, 184. 

Ascyphous, podetia without scyphi, i \qetpassim. 

Biatorine, apothecia that are soft or waxy, and often brightly coloured, as in Biatora, 158. 

Blasteniospore, see polarilocular spore. 

Byssoid, slender, thread-like, as in the old genus Byssus.. 

Campylidium, supposed new type of fructification in lichens, 191. 

Capitulum, the globose apical apothecium of Coniocarpineae ; cf. mazaedium, 319. 

Carpogonium, primordial stage of fructification, 160, 164 et passim. 

Cephalodium, irregular outgrowth from the thallus enclosing mostly blue-green algae ; or 

intruded packet of algae within the thallus, 1 1, 133 et passim. 

Chrondroid, hard and tough like cartilage, a term applied to strengthening strands of 

hyphae, 104, 1 14. 

Chroolepoid, like the genus Chroolepis (Trentepohlia). 

Chrysogonidia, yellow algal cells ( Trentepohlia). 

Cilium, hair-like outgrowth from surface or margin of thallus, or margin of apothecium, 91. 

Consortium (consortism), mutual association of fungus and alga (Reinke); also termed 

"mutualism," 31, 313. 

Corticolous, living on the bark of trees, 363. 

Crustaceous, crust-like closely adhering thallus, 70-79. 

Cyphella, minute cup-like depression on the under surface of the thallus (Sticta, etc.), 

i.i, 126. 

Decomposed, term applied to cortex formed of gelatinous indistinct hyphae (amorphous), 

73-8i et passim, 357. 

Determinate, thallus with a definite outline, 72. 

Dimidiate, term applied to the perithecium, when the outer wall covers only the upper 

portion, 159.

xx GLOSSARY 

Discoid, disc-like, an open rounded apothecium, 1 56. 

Discolichens, in which the fructification is an apothecium, 160 et seq. 

Dual hypothesis, the theory of two organisms present in the lichen thallus, 27 et seq. 

Effigurate, having a distinct form or figure; cf. placodioid, 80, 201 

Endobasidial, Steiner's term for sporophore with a secondary sporiferous branch, 200. 

Endogenous, produced internally, as spores in an ascus, 179; see also under thallus. 

Endolithic, embedded in the rock, 75. 

Endosaprophytism, term used by Elenkin for destruction of the algal contents by enzymes 

of the fungus, 36. 

Entire, term applied to the perithecium when completely surrounded by an outer wall, 159. 

Epilithic, growing on the rock surface, 70. 

Epiphloeodal, thallus growing on the surface of the bark, 77. 

Epiphyllous, growing on leaves, 363. 

Epithecium, upper layer of thecium (hymenium), 158. 

Erratic lichens, unattached and drifting, 259. 

Exobasidial, Steiner's term for sporophore without a secondary sporiferous branch, 200. 

Exogenous, produced externally, as spores on tips of hyphae ; see also under thallus. 

Fastigiate cortex, formed of clustered parallel hyphal branches vertical to long axis of 

thallus, 82. 

Fat-cells, specialized hyphal cells containing fat or oil, 75, 215 et passim. 

Fibrous cortex, formed of hyphae parallel with long axis of thallus, 82. 

Filamentous, slender thallus with radiate structure, 101 et seq. 

Foliose, lichens with a leafy form and stratose in structure, 82-97. 

Foveolae, Foveolate, pitted, 373. 

Fruticose, upright or pendulous thallus, with radiate structure, 101 et seq. 

Fulcrum, term used by Steiner for sporophore, 200. 

Gloeolichens, lichens in which the gonidia are Gloeocapsa or Chroococcus, 284, 373, 389. 

Gonidium, the algal constituent of the lichen thallus, 20-45 et passim. 

Gonimium, blue-green algal cell (Myxophyceae), constituent of the lichen thallus, 52. 

Goniocysts, nests of gonidia in Moriolaceae, 313. 

Gyrose, curved backward and forward, furrowed fruit of Gyrophora, 184. 

Hapteron, aerial organ of attachment, 94, 122. 

Haustorium, outgrowth or branch of a hypha serving as an organ of suction, 32. 

Helotism, state of servitude, term used to denote the relation of alga to fungus in 

lichen organization, 38, 40. 

Heteromerous, fungal and algal constituents of the thallus in definite strata, 13, 68, 305 

et passim. 

Hold-fast, rooting organ of thallus, 109, 122 et passim. 

Homobium, interdependent association of fungus and alga, 31 

Homoiomerous, fungal and algal constituents more or less mixed in the 1 thallus, 3, 68, 

305 et passim. 

Hymenial gonidia, algal cells in the hymenium, 30, 314, 315, 327. 

Hymenium, apothecial tissue consisting of asci and paraphyses ; cf. thecium, 157. 

HymenolichenSj, lichens of which the fungal constituent is a Hymenomycete, 152-154, 342. 

Hypophloeodal, thallus growing within the bark, 78, 364. 

Hypothallus, first growth of hyphae (proto- or pro-thallus) persisting as hyphal growth at 

base or margin of the thallus, 70, 257 et passim. 

Hypothecium, layer below the thecium (hymenium), 157.

GLOSSARY xxi 

Intricate cortex, composed of hyphae densely interwoven but not coalescent, 83. 

Isidium, coral-like outgrowth on the lichen thallus, 149-151. 

Lecanorine, apothecium with a thalline margin as in Lecanora, 158. 

Lecideine, apothecium usually dark-coloured or carbonaceous and without a thalline 

margin, 158. 

Leprose, mealy or scurfy, like the old form genera, Lepra, Lepraria, 191. 

Lichen-acids, organic acids peculiar to lichens, 221 et seq. 

Lignicolous, living on wood or trees, 366. 

Lirella, long narrow apothecium of Graphideae, 158. 

Mazaedium, fructification of Coniocarpineae, the spores lying as a powdery mass in the 

capitulum, 176. 

Medulla, the loose hyphal layer in the interior of the thallus, 88 et passim. 

Meristematic, term applied by Wainio to growing hyphae, 48. 

Microgonidia, term applied by Minks to minute greenish bodies in lichen hyphae, 26. 

Multi-septate, term applied to spores with numerous transverse septa, 316 et seq. 

Murali-divided, Muriform, term applied to spores divided like the masonry of a wall, 187. 

Oidium, reproductive cell formed by the breaking up of the hyphae, 189. 

Oil-cell, hyphal cell containing fat globules, 215. 

Orculiform, see polarilocular. 

Orthidium, supposed new type of fructification in lichens, 192. 

Palisade-cells, the terminal cells of the hyphae forming the fastigiate cortex, 82, 83. 

Panniform, having a felted or matted appearance, 260. 

Paraphysis, sterile filament in the hymenium, 157. 

Parasymbiosis, associated harmless but not mutually useful growth of two organisms, 263. 

Parathecium, hyphal layer round the apothecium, 157. 

Peltate, term applied to orbicular and horizontal apothecia in the form of a shield, 336. 

Perithecium, roundish fructification usually with an apical opening (ostiole) containing 

ascospores, 158 et passim. 

Pervious, referring to scyphi with an opening at the base (Perviae\ 118. 

Phycolichens, lichens in which the gonidia are blue-green (Myxophyceae), 52 et passim. 

Placodioid, thallus with a squamulose determinate outline, generally orbicular ; cf. 

effigurate, 80. 

Placodiomorph, see polarilocular. 

Plectenchyma (Plectenchymatous), pseudoparenchyma of fungi and lichens, 66 etpassim. see spermatium, 312. 

Pleurogenous, borne laterally on hyphal cells ; 

Pluri -septate, term applied to spores with several transverse septa, 321 et seq. 

Podetium, stalk-like secondary thallus of Cladoniaceae, 1 14, 293 et seq. 

Polarilocular, Polaribilocular, two-celled spores with thick median wall traversed by a 

connecting tube, 188, 340-341. 

Polytornous, arising of several branches of the podetium from one level, 118. 

Proper margin, the hyphal margin surrounding the apothecium, 157. 

Prothallus, Protothallus, first stages of hyphal growth ; cf. hypothallus, 71. 

Pycnidiospores, stylospores borne in pycnidia, 198 et passim. 

Pycnidium, roundish fructification, usually with an opening at the apex, containing 

sporophores and stylospores ; cf. spermogonium, 192 et seq. 

Pyrenolichens, in which the fructification is a closed perithecium, 173 et passim. 

Radiate thallus, the tissues radiate from a centre, 98 et seq.

xxii GLOSSARY 

Rhagadiose, deeply chinked, 74 ; cf. rimose. 

Rhizina, attaching "rootlet," 92-94. 

Rimose, Rimulose, cleft or chinked into areolae, 73. 

Rimose-diffract, widely cracked or chinked, 74. 

Scutellate, shaped like a -platter, 156. 

Scyphus, cup-like dilatation of the podetium, in, 117. 

Signature, a term in ancient medicine to signify the resemblance of a plant to any part 

of the human body, 406, 409. 

Soralium, group of soredia surrounded by a definite margin, 144. 

Soredium, minute separable particle arising from the gonidial tissue of the thallus, and 

consisting of algae and hyphae, 141. 

Spermatium, spore-like body borne in the spermogonium, regarded as a non-motile male 

cell or as a pycnidiospore, 201. 

Spermogonium, roundish closed receptacle containing spermatia, 192. 

Sphaeroid-cell, swollen hyphal cell, containing fat globules, 215. 

Squamule, a small thalline lobe or scale, 74 et passim. 

Sterigma, Nylander's term for the spermatiophore, 197. 

Stratose thallus, where the tissues are in horizontal layers, 70. 

Stratum, a layer of tissue in the thallus, 70. 

Symbiont, one of two dissimilar organisms living together, 32. 

Symbiosis, a living together of dissimilar organisms, also termed commensalism, 31, 32 

et seq. 

Tegulicolous, living on tiles, 369. 

Terebrator, boring apparatus, term used by Lindau for the lichen " trichogyne," 179. 

Thalline margin, an apothecial margin formed of and usually coloured like the thallus ; 

cf. amphithecium. 

Thallus, vegetative body or soma of the lichen plant, 11,421. Endogenous thallus in which 

the alga predominates, 68. Exogenous thallus in which the fungus predominates, 69. 

Theca, enlarged cell containing spores ; cf. ascus. 

Thecium, layer of tissue in the apothecium consisting of asci and paraphyses ; cf. 

hymenium, 157. 

Trichogyne, prolongation of the egg-cell in Florideae which acts as a receptive tube ; 

septate hypha in lichens arising from the ascogonium, 160, 177-181, 273. 

Woronin's hypha, a coiled hypha occurring in the centre of the fruit primordium, 1 59, 163. 

ERRATA 

p. 24. For Baranetsky razaTB 

p. 277. For Ascolium read Acolium. 

p. 318. For Lepolichen coccophora read coccophorus.

INTRODUCTION 

LICHENS are, with few exceptions, perennial aerial plants of somewhat 

lowly organization. In the form of spreading encrustations, horizontal leafy 

expansions, of upright strap-shaped fronds or of pendulous filaments, they 

take possession of the tree-trunks, palings, walls, rocks or even soil that 

afford them a suitable and stable foot-hold. The vegetative body, or thallus, 

which may be extremely long-lived, is of varying colour, white, yellow, 

brown, grey or black. The great majority of lichens are Ascolichens and 

reproduction is by ascospores produced in open or closed fruits (apothecia 

or perithecia) which often differ in colour from the thallus. There are a few 

Hymenolichens which form basidiospores. Vegetative reproduction by 

soredia is frequent. 

Lichens abound everywhere, from the sea-shore to the tops of high 

mountains, where indeed the covering of perpetual snow is the only barrier 

to their advance ; but owing to their slow growth and long duration, they 

are more seriously affected than are the higher plants by chemical or other 

atmospheric impurities and they are killed out by the smoke of large towns: 

only a few species are able to persist in somewhat depauperate form in or 

near the great centres of population or of industry. 

The distinguishing feature of lichens is their composite nature: they 

consist of two distinct and dissimilar organisms, a fungus and an alga, which, 

in the lichen thallus, are associated in some kind of symbiotic union, each 

symbiont contributing in varying degree to the common support : 

it is 

a more or less unique and not unsuccessful venture in plant-life. The 

algae Chlorophyceae or Myxophyceae that become lichen symbionts or 

"gonidia" are of simple structure, and, in a free condition, are generally to 

be found in or near localities that are also the customary habitats of lichens. 

The fungus is the predominant partner in the alliance as it forms the fruiting 

bodies. It belongs to the Ascomycetes 1 

, except in a few tropical lichens 

These two 

(Hymenolichens), in which the fungus is a Basidiomycete. 

types of plants (algae and fungi) belonging severally to many different 

genera and species have developed in their associated life this new lichen 

organism, different from themselves as well as from all other plants, not 

only morphologically but physiologically. Thus there has arisen a distinct 

class, with families, genera and species, which through all their varying forms 

retain the characteristics peculiar to lichens. 

1 E. Acton (1909) has described a primitive lichen Rotrydina vnlgaris, in which there is no 

fruiting stage, and in which the fungus seems to show affinity with a Hyphomycete.

xxiv INTRODUCTION 

In the absence of any " visible " seed, there was much speculation in 

early days as to the genesis of all the lower plants and many opinions 

were hazarded as to their origin. 

1 

, Luyken for instance, thought that lichens 

were compounded of air and moisture. Hornschuch 2 traced their origin to 

a vegetable infusorium, Monas Lens, which became transformed to green 

matter and was further developed by the continued action of light and air, 

not only to lichens, but to algae and mosses, the type of plant finally evolved 

being determined by the varying atmospheric influences along 

with the 

chemical nature of the substratum. An account 3 is published of Nees von 

Esenbeck, on a botanical excursion, pointing out to his students the green 

substance, Lepraria botryoides, which covered the lower reaches of walls and 

rocks, while higher up it assumed the grey lichen hue. This afforded him 

sufficient proof that the green matter in that dry situation changed to 

lichens, just as in water it changed to algae. An adverse criticism by 

Dillenius 4 on a description of a lichen fructification is not inappropriate to 

" 

those early theorists : Ex quo apparet, quantum videre possint homines, 

si imaginatione polleant." 

A constant subject of speculation and of controversy was the origin of 

the green cells, so dissimilar to the general texture of the thallus. It was 

thought finally to have been established beyond dispute that they were 

formed directly from the colourless hyphae and, as a corollary, Protococcus 

and other algal cells living in the open were considered to be escaped 

gonidia or, as Wallroth 5 termed them, " unfortunate brood-cells," his view 

being that they were the reproductive organs of the lichen plant that had 

failed to develop. 

It was a step forward in the right direction when lichens were regarded 

as transformed algae, among others by Agardh 6 

, who believed that he had 

followed the change from Nostoc lichenoides to the lichen Collema limosum. 

Thenceforward their double resemblance, on the one hand to algae, on the 

other to fungi, was acknowledged, and influenced strongly the trend of study 

and investigation. 

The announcement 7 

by Schwendener 8 of the dual hypothesis solved the 

problem for most students, though the relation between the two symbionts 

is still a subject of controversy. The explanation given by Schwendener, 

and still held by some 9 

that lichens , were merely fungi parasitic on algae, 

was indeed a very inadequate conception of the lichen plant, and it was hotly 

contested by various lichenologists. Lauder Lindsay 10 dismissed the theory 

as " 

merely the most recent instance of German transcendentalism applied 

1 

Luyken 1809. 

8 Wallroth 1825. 

9 Fink 1913. 

2 Hornschuch 1819. 

3 Raab 1819. 

6 Agardh 1820. 7 See p. 27. 

10 

Lindsay 1876. 

4 Dillenius 1741, p. 200. 

8 Schwendener 1867.

to the Lichens." Earlier still, Nylander 1 

INTRODUCTION xxv 

, in.a paper dealing with cephalodia 

and their peculiar gonidia, had denounced it : 

" Locum sic suum dignum 

occupat algolichenomachia inter historias ridiculas, quae hodie haud paucae 

circa lichenes, majore imaginatione quam scientia, enarrantur." He never 

changed 

his attitude and Crombie 2 

, wholly agreeing 

with his estimate of 

these " absurd tales," translates a much later pronouncement by him 3 : 

"All these allegations belong to inept Schwendenerism and scarcely deserve 

even to be reviewed or castigated so puerile are they the offspring of in- 

experience and of a light imagination. No true science there." Crombie 4 

himself in a first paper on this subject declared that " the new theory would 

necessitate their degradation from the position they have so long held as an 

independent class." He scornfully rejected the whole subject as "a Romance 

of Lichenology, or the unnatural union between a captive Algal damsel and 

a tyrant Fungal master." The nearest approach to any concession on the 

algal question occurs in a translation by Crombie 5 of one of Nylander's 

papers. It is stated there that a saxicolous alga (Gongrosira Kiitz.) had 

been found bearing the apothecia of Lecidea herbidula n. sp. Nylander adds : 

"This algological genus is one which readily passes into lichens." At a later 

date, Crombie 6 was even more comprehensively contemptuous and wrote: 

" whether viewed anatomically or biologically, analytically or synthetically, 

it is instead of being true science, only the Romance of Lichenology." These 

views were shared by many continental lichenologists and were indeed, as 

already stated, justified to a considerable extent: it was impossible to regard 

such a large and distinctive class of plants as merely fungi parasitic on the 

lower algae. 

Controversy about lichens never dies down, and that view of their parasitic 

nature has been freshly promulgated among others by the American 

genetic origin of the gonidia has also been 

lichenologist Bruce Fink 7 The . 

restated 

8 

: by Elfving the various theories and views are discussed fully in 

the chapter on the lichen plant. 

Much of the interest in lichens has centred round their symbiotic growth. 

No theory of simple parasitism can explain the association of the two 

plants: if one of the symbionts is withdrawn either fungus or alga the 

lichen as such ceases to exist. Together they form a healthy unit capable 

of development and change : a basis for progress along new lines. Permanent 

characters have been formed which are transmitted just as in other units of 

organic life. 

A new view of the association has been advanced by F. and Mme Moreau 9 . 

They hold that the most characteristic lichen structures more particularly 

1 

Nylander 1869. 

8 Crombie 1877. 

9 Moreau 1918. 



3 Nylander 1891. 

7 Fink 1913. 


8 Elfving 1913.

xxvi 

INTRODUCTION 

the cortex have been induced by the action of the alga on the fungus. 

The larger part of the thallus might therefore be regarded as equivalent to 

a gall: "it is a cecidium, an algal cecidium, a generalized biomorphogenesis." 

The morphological characters of lichens are of exceptional interest, conditioned 

as they are by the interaction of the two symbionts, and new 

structures have been evolved by the fungus which provides the general 

tissue system. Lichens are plants of physiological symbiotic origin, and that 

aspect of their life-history has been steadily kept in view in this work. There 

are many new requirements which have had to be met by the lichen hyphae, 

and the differences between them and the true fungal hyphae have been 

considered, as these are manifested in the internal economy of the com- 

pound plant, and in its reaction to external influences such as light, heat, 

moisture, etc. 

The pioneers of botanical science were of necessity occupied almost 

exclusively with collecting and describing plants. As the number of known 

lichens gradually accumulated, affinities were recognized and more or less 

successful efforts were made to tabulate them in classes, orders, etc. It was 

a marvellous power of observation that enabled the early workers to arrange 

the first schemes of classification. Increasing knowledge aided by improved 

microscopes has necessitated changes, but the old fundamental "genus" 

Lichen is practically equivalent to the Class Lichenes. 

The study of lichens has been a slow and gradual process, with a con- 

tinual conflict of opinion as to the meaning of these puzzling plants their 

structure, reproduction, manner of subsistence and classification as well as 

their relation to other plants.. It has been found desirable to treat these 

different subjects from a historical aspect, as only thus can a true under- 

standing be gained, or a true judgment formed as to the present condition 

of the science. It is the story of the evolution of lichenology as well as of 

lichens that has yielded so much of interest and importance. 

The lichenologist may claim several advantages in. the study of his 

subject : the abundant material almost everywhere to hand in country 

districts, the ease with which the plants are preserved, and, not least, the 

interest excited by the changes and variations induced by growth conditions ; 

there are a whole series of problems and puzzles barely touched on as yet 

that are waiting to be solved. 

In field work, it is important to note accurately and carefully the nature 

of the substratum as well as the locality. Crustaceous species should be 

gathered if possible along with part of the wood or rock to which they are 

attached ; 

if they are scraped off, the pieces may be reassembled on gummed 

paper, but that is less satisfactory. The larger forms are more easily secured;

INTRODUCTION xxvii 

they should be damped and then pressed before being laid : away the process 

flattens them, but it saves them from the risk of being crushed and broken, 

as when dry they are somewhat brittle. Moistening with water will largely 

restore their original form. All parts of the lichen, both thallus and fruit, 

can be examined with ease at any time as they do not sensibly alter in the 

herbarium, though they lose to some extent their colouring : the blue-grey 

forms, for instance, often become a uniform dingy brownish-grey. 

Microscopic examination in the determination of species is necessary in 

many instances, but that disability if it ranks as such is shared by other 

cryptogams, and may possibly be considered an inducement rather than a 

deterrent to the study of lichens. For temporary examination of microscopic 

preparations, the normal condition is best observed by mounting them in 

water. If the plants are old and dry, the addition of a drop or two of potash 

or ammonia solution is often helpful in clearing the membranes of the 

cells and in restoring the shrivelled spores and paraphyses to their natural 

forms and dimensions. 

If serial microtome sections are desired, more elaborate methods are 

required. For this purpose Peirce 1 has recommended that " when dealing 

with plants that are dry but still alive, the material should be thoroughly 

wetted and kept moist for two days, then killed and fixed in a saturated 

solution of corrosive sublimate in thirty-five per cent, alcohol." The solu- 

tion should be used hot : the usual methods of dehydrating and embedding 

in paraffin are then employed with extra precautions on account of the 

extremely brittle nature of lichens. 

Another method that also gave good results has been proposed by 

French 2 : 

" 

first the lichen is put into 95 per cent, alcohol for 24 hours, then 

into thin celloidin and thick celloidin 2/\. hours each. After this the specimens 

are embedded in thick celloidin which is hardened in 70 per cent, alcohol 

for 24. hours and then cut." French advises staining with borax carmine : 

it colours the fungal part pale carmine and the algal cells a greenish-red 

shade. 

Modern research methods of work are generally described in full in the 

publications that are discussed in the following chapters. The student is 

referred to these original papers for information as to fixing, embedding, 

staining, etc. 

Great use has been made of reagents in determining lichen species. 

They are extremely helpful and often give the clinching decision when 

morphological characters are obscure, especially if the plant has been much 

altered by the environment. It must be borne in mind, however, that a 

1 Peirce 1898. 

* French 1898.

xxviii INTRODUCTION 

species is a morphological rather than a physiological unit, and it is not the 

structures but the cell-products that are affected by reagents. Those most 

commonly in use are saturated solutions of potash and of bleaching-powder 

(calcium hypochlorite). The former is cited in text-books as KOH or simply 

as K, the latter as CaCl or C. The C solution deteriorates quickly and 

must, therefore, be frequently renewed to produce the required reaction, 

i.e. some change of colour. These two reagents are used singly or, if con- 

jointly, K followed by C. The significance of the colour changes has been 

considered in the discussion on lichen-acids. 

Iodine is generally cited in connection with its staining effect on the 

hymenium of the fruit; the blue colour produced is, however, more general 

than was at one time supposed and is not peculiar to lichens ; the asci of 

many fungi react similarly though to a less extent. The medullary hyphae 

in certain species also stain blue with iodine.

CHAPTER I 


A. INTRODUCTORY 

THE term "lichen" is a word of Greek origin used by Theophrastus in his 

History of Plants to signify a superficial growth on the bark of olive-trees. 

The name was given in the early days of botanical study not to lichens, as 

we understand them, but to hepatics of the Marchantia type. Lichens 

themselves were generally described along with various other somewhat 

similar plants as "Muscus" (Moss) by the older writers, and more definitely 

as "Musco-fungus" by Morison 1 . In a botanical work published in 170x3 by 

Tournefort'- all the members of the vegetable kingdom then known were 

for the first time classified in genera, and the genus Lichen was reserved for 

the plants that have been so designated since that time, though Dillenius 3 

in his works preferred the adjectival name Lichenoides. 

A painstaking historical account of lichens up to the beginning of 

modern lichenology has been written by Krempelhuber 4 

, 

a German licheno- 

logist. He has grouped the data compiled by him into a series of Periods, 

each one marked by some great advance in knowledge of the subject, 

though, as we shall see, the advance from period to period has been continuous 

and gradual. While following generally on the lines laid down by 

Krempelhuber, it will be possible to cite only the more prominent writers 

and it will be of much interest to British readers to note especially the work 

of our own botanists. 

Krempelhuber's periods are as follows: 

I. From the earliest times to the end of the seventeenth century. 

II. Dating from the arrangement of plants into classes called genera 

by Tournefort in 1694 to 1729. 

III. From Micheli's division of lichens into different orders in 1729 

to 1780. 

IV. The definite and reasoned establishment of lichen genera based 

on the structure of thallus and fruit by Weber in 1780 to 1803. 

V. The arrangement of all known lichens under their respective 

genera by Acharius in 1803 to 1846. 

VI. The recognition of spore characters in classification by De 

1 Morison 1699. 

Notaris in 1846 to 1867. 

2 Tournefort 1694 and 1700. 

3 Dillenius 1/41. 

4 

Krempelhuber 1867-1872. 

S. L. I

2 HISTORY OF LICHENOLOGY 

A seventh period which includes modern lichenology, and which dates 

after the publication of Krempelhuber's History, was ushered in by 

Schwendener's announcement in 1867 of the hypothesis as to the dual 

nature of the lichen thallus. Schwendener's theory gave a new impulse to 

the study of lichens and strongly influenced all succeeding investigations. 

B. PERIOD I. PREVIOUS TO 1694 

Our examination of lichen literature takes us back to Theophrastus, 

the disciple of Plato and Aristotle, who lived from 371 to 2848.0., and who 

wrote a History of Plants, one of the earliest known treatises on Botany. 

Among the plants described by Theophrastus, there are evidently two 

lichens, one of which is either an Usnea or an Alectoria, and the other 

certainly Roccella tinctoria, the last-named an important economic plant 

likely to be well known for its valuable dyeing properties. The same or 

somewhat similar lichens are also probably alluded to by the Greek physician 

Dioscorides, in his work on Materia Medica, A.D. 68. About the 

same time Pliny the elder, who was a soldier and traveller as well as a 

voluminous writer, mentions them in his Natural History which was 

completed in 77 A.D. 

During the centuries that followed, there was little study of Natural 

History, and, in any case, lichens were then and for a long time after 

considered to be of too little economic value to receive much attention. 

In the sixteenth century there was a great awakening of scientific 

interest all over Europe, and, after the printing-press had come into 

general use, a number of books bearing on Botany were published. It will 

be necessary to chronicle only those that made distinct contributions to the 

knowledge of lichens. 

The study of plants was at first entirely from a medical standpoint 

and one of the first works, and the first book on Natural History, printed 

in England, was the Crete Herball 1 

. It was translated from a French work, 

Hortus sanitatis, and published by Peter Treveris in Southwark. One of 

the herbs recommended for various ailments is "Muscus arborum," the 

tree-moss (Usnea}. A somewhat crude figure accompanies the text. 

Ruel 2 of Soissons in 3 

France, Dorstenius , Camerarius 4 and Tabernaemontanus 

5 in Germany followed with works on medical or economic botany 

and they described, in addition to the tree-moss, several species of reputed 

value in the art of healing now known as Sticta (Lobaria) pulmonaria, 

Lobaria laetevirens, Cladonia pyxidata, Evernia prunastri and Cetraria 

islandica. Meanwhile L'Obel 6 

, a Fleming, who spent the latter part of his 

life in England and is said to have had charge of a physic garden at 

1 Crete Herball 1526. Ruel I536 

4 Camerarius 1586. 

5 Tabernaemontanus 1590. 

8 Dorstenius 1MO 

6 L'Obel 1576.

PERIOD I. PREVIOUS TO 1694 3 

Hackney, was appointed botanist to James I. He published at Antwerp 

a large series of engravings of plants, and added a species of Ramalina to 

the growing list of recognized lichens. Dodoens 1 

, 

also a Fleming, records 

not only the Usnea of trees, but a smaller and more slender black form 

which is easily identifiable as Alectoria jubata. He also figures Lichen 

pulmonaria and gives the recipe for its use. 

The best-known botanical book published at that time, however, is the 

Herball of John Gerard 2 of London, Master in Chirurgerie, who had a 

garden in Holborn. He recommends as medicinally valuable not only 

Usnea, but also Cladonia pyxidata, for which he coined the name "cuppeor 

chalice-moss." About the same time Schwenckfeld 3 

recorded, among 

plants discovered by him in Silesia, lichens now familiar as Alectoria 

jubata, Cladonia rangiferina and a species of Peltigera, 

Among the more important botanical writers of the seventeenth century 

may be cited Colonna 4 and Bauhin 5 . The former, an Italian, contributes, 

in his Ecphrasis, descriptions and figures of three additional species easily 

recognized as Physcia ciliaris, Xanthoria parietina and Ramalina calicaris. 

Kaspar Bauhin, a professor in Basle, who was one of the most advanced of 

the older botanists, was the first to use a binomial nomenclature for some 

of his plants. He gives a list in his Pinax of the lichens with which he was 

acquainted, one of them, Cladonia fimbriata, being a new plant. 

John Parkinson's 6 Herball is well known to English students; he adds 

one new species for England, Lobaria pulmonaria, already recorded on the 

Continent. Parkinson was an apothecary in London and held the office of 

the King's Herbarist; his garden was situated in Long 

Acre. How's 7 

Phytographia is notable as being the first account of British plants compiled 

without reference to their healing properties. Five of the plants described 

by him are lichen species: "Lichen arborum sive pulmonaria" (Lobaria 

pulmonaria}, "Lichen petraeus tinctorius" (Roccella}, "Muscus arboreus" 

(Usnea}, "Corallina montana" (Cladonia rangiferina} and "Muscus pixoides" 

(Cladonia}. Several other British species were added by Merrett 8 who records 

, 

in his Pinax, "Muscus arboreus umbilicatus" (Physcia dliaris}, "Muscus 

aureus tenuissimus" ( Teloschistes flavicans), "Muscus caule rigido" (Alec- 

toria) and "Lichen petraeus purpureus" (Parmelia omphalodes}, the lastnamed, 

a rock lichen, being used, he tells us, for dyeing in Lancashire. 

Merret or Merrett was librarian to the Royal College of Physicians. 

His Pinax was undertaken to replace How's Phytographia published 

sixteen years previously and then already out of print. Merrett's work 

was issued in 1666, but the first impression was destroyed in the great fire 

of London and most of the copies now extant are dated 1667. He arranged 

1 Dodoens 1583. 

5 Bauhin 1623, pp. 360-2. 

2 Gerard 1597. 

* Parkinson 1640. 

3 Schwenckfeld 1600. 

7 How 1650. 

4 Colonna 1606. 

8 Merrett 1666.

4 


the species of plants in alphabetical order, but as the work was not critical 

it fell into disuse, being superseded by John Ray's Catalogus and Synopsis. 

To Robert Plot 1 we owe the earliest record of Cladonia cocci/era which had 

hitherto escaped notice; it was described and figured as a new and rare 

Plot was the first Gustos 

plant in the Natural History of Staffordshire^. 

of Ashmole's Museum in Oxford and he was also the first to prepare 

a County Natural History. 

The greatest advance during this first period was made by Robert 

Morison 2 

, a Scotsman from Aberdeen. He studied medicine at Angers in 

France, superintended the Duke of Orleans' garden at Blois, and finally, 

after his return to this country in 1669, became Keeper of the botanic 

garden at Oxford. In the third volume of his great work 2 on Oxford 

plants, which was not issued till after his death, the lichens are put in 

a separate group "Musco-fungus" and classified with some other plants 

under "Plantae Heteroclitae." The publication of the volume projects into 

the next historical period. 

Long before this date John Ray had begun to study and publish books 

on Botany. His Catalogue of English Plants* is considered to have commenced 

a new era in the study of the science. The Catalogue was followed 

and in 

by the History of Plants*, and later by a Synopsis of British Plants 5 

all of these books lichens find a place. Two editions of the Synopsis 

appeared during Ray's lifetime, and to the second there is added an 

Appendix contributed by Samuel Doody which is entirely devoted to 

Cryptogamic plants, including not a few lichens still called "Mosses" 

discovered for the first time. Doody, himself an apothecary, took charge 

of the garden of the Apothecaries' Society at Chelsea, but his chief interest 

was Cryptogamic Botany, a branch of the subject but little regarded before 

his day. Pulteney wrote of him as the "Dillenius of his time." 

Among Doody's associates were the Rev. Adam Buddie, James Petiver 

and William Sherard. Buddie was primarily a collector and his herbarium 

is incorporated in the Sloane Herbarium at the British Museum. It contains 

lichens from all parts of the world, many of them contributed by Doody, 

Sherard and Petiver. Only a few of them bear British localities : several are 

from Hampstead where Buddie had a church. 

The Society of Apothecaries had been founded in 1617 and the mem- 

bers acquired land on the river-front at Chelsea, which was extended later 

and made into a Physick Garden. James Petiver 6 was one of the first 

Demonstrators of Plants to the Society in connection with the 'garden, and 

one of his duties was to conduct the annual herborizing tours of the 

apprentices in search of plants. He thus collected a large herbarium on 

the annual excursions, as well as on shorter visits to the more immediate 

1 Plot 1686. 

* Morison 1699. 

3 

Ray 1670. 

4 

Ray 1686. 

5 

Ray 1690. 

, 

6 Petiver 1695.

PERIOD I. PREVIOUS TO 1694 5 

neighbourhood of London. He wrote many tracts on Natural History 

subjects, and in these some lichens are included. He was one of the best 

known of Ray's correspondents, and owing to his connection with the 

Physic Garden received plants from naturalists in foreign countries. 

Sherard, another of Doody's friends, had studied abroad under Tournefort 

and was full of enthusiasm for Natural Science. It was he who brought 

Dillenius to England and finally nominated him for the position of the first 

Sherardian Professor of Botany at Oxford. Another well-known contemporary 

botanist was Leonard Plukenet 1 who had a botanical garden at Old 

Palace Yard, Westminster. He wrote several botanical works in which 

lichens are included. 

Morison is the only one of all the botanists of the time who recognized 

lichens as a group distinct from mosses, algae or liverworts, and even he 

had very vague ideas as to their development. 

2 

Malpighi had noted the 

presence of soredia on the thallus of some species, and , regarded them as 

seeds. Porta 3 

, 

a Neapolitan, has been quoted by Krempelhuber as probably 

the first to discover and place on record the direct growth of lichen fronds 

from green matter on the trunks of trees. 

C. PERIOD II. 1694-1729 

The second Period is ushered in with the publication of a French work, 

Les Elemens de Botatiique by Tournefort 4 

, who 

was one of the greatest 

botanists of the time. His object was "to facilitate the knowledge of plants 

and to disentangle a science which had been neglected because it was found 

to be full of confusion and obscurity." Up to this date all plants were 

classified or listed as individual species. It was Tournefort who first 

arranged them in groups which he designated "genera" and he gave a 

careful diagnosis of each genus. 

Les Elemens was successful enough to warrant the publication a few 

years later of a larger Latin edition entitled Institutiones 5 and thus fitted for 

a wider circulation. Under the genus Lichen, he included plants "lacking 

flowers but with a true cup-shaped shallow fruit, with very minute pollen or 

seed which appeared to be subrotund under the microscope." Not only the 

description but the figures prove that he was dealing with ascospores and 

not merely soredia, though under Lichen along with true members of the 

"genus" he has placed a Marchantia, the moss Splachnum and a fern. A few 

lichens were placed by him in another genus Coralloides. 

Tournefort's system was of great service in promoting the study of 

Botany: his method of classification was at once adopted by the German 

writer Rupp 6 who published a Flora of plants from Jena. Among these 

1 Plukenet 1691-1696. 

4 Tournefort 1694. 

2 Malpighi 1686. 


3 Porta 1688. 

6 

Rupp 1718.


plants are included twenty-five species of lichens, several of which he 

considered new discoveries, no fewer than five being some form of Lichen 

Buxbaum 1 

, in his enumeration of plants from Halle, 

gelatinosus (Collema}. 

finds place for forty-nine lichen species, with, in addition, eleven species of 

Coralloides; and Vaillant 2 in listing the plants that grew in the neighbourhood 

of Paris gives thirty-three species for the genus Lichen of which a 

large number are figured, among them species of Ramalina, Parmelia, 

Cladonia, etc. 

In England, however, Dillenius 3 

, who 

at this time brought out a third 

edition of Ray's Synopsis and some years later his own Historia Muscorum, 

and no 

still described most of his lichens as "Lichenoides" or "Coralloides" ; 

other work of note was published in our country until after the Linnaean 

system of classification and of nomenclature was introduced. 

plants. 

D. PERIOD III. 1729-1780 

Lichens were henceforth regarded as a distinct genus or section of 

4 

Micheli an Italian , 

botanist, Keeper of the Grand Duke's Gardens 

in Florence, realized the desirability of still further delimitation, and he 

broke up Tournefort's large comprehensive genera into numerical Orders. 

In the genus Lichen, he found occasion for 38 of these Orders, determined 

mainly by the character of the thallus, and the position on it of apothecia 

and soredia. He enumerates the species, many of them new discoveries, 

though not all of them recognizable now. His great work on Plants is 

enriched by a series of beautiful figures. It was published in 1729 and 

marks the beginning of a new Period a new outlook on botanical science. 

Micheli regarded the apothecia of lichens as "floral receptacles," and the 

soredia as the seed, because he had himself followed the development of 

lichen fronds from soredia. 

The next writer of distinction is the afore-mentioned Dillen or 

Dillenius. He was a native of Darmstadt and began his scientific career 

in the University of Giessen. His first published work 5 was an account of 

plants that were to be found near Giessen in the different months of the 

year. Mosses and lichens he has assigned to December and January. 

Sherard induced him to come to England in 1721, and at first engaged his 

services in arranging the large collections of plants which he, Sherard, had 

brought from Smyrna or acquired from other sources. 

Three years after his arrival Dillenius had prepared the third edition of 

Ray's Synopsis for the press, but without putting his name on the title-page 6 . 

Sherard explained, in a letter to Dr Richardson of Bierly in Yorkshire, that 

"our people can't agree about an editor, they are unwilling a foreigner should 

1 Buxbaum 1721. 

4 Micheli 1729. 

2 Vaillant 1727. 

5 Dillenius 1719. 

Dillenius 1724 and 1741. 

s 

See Druce and _ 

yines IQ

PERIOD III. 1729-1780 7 

put his name to it." Dillenius, who was quite aware of the prejudice against 

aliens, himself writes also to Dr Richardson : "there being some apprehension 

(me being a foreigner) of making natives uneasy if I should publicate it in 

my name." Lichens were already engaging his attention, and descriptions 

of 91 species were added to Ray's work. So well did this edition meet the 

requirements of the age, that the Synopsis remained the text-book of 

British Botany until the publication of Hudson's Flora Anglica in 1762. 

William Sherard died in 1728. He left his books and plates to the 

University of Oxford with a sum of money to endow a Professorship of 

Botany. In his will he had nominated Dr Dillenius for the post. The great 

German botanist was accordingly appointed and became the first Sherardian 

Professor of Botany, though he did not remove to Oxford till 1734. The 

following years were devoted by him to the preparation of Historia Muscorum, 

which was finally published in 1741. It includes an account of the 

then known liverworts, mosses and lichens. The latter still considered by 

Dillenius as belonging to mosses were grouped under three genera, Usnea, 

Coralloides and Lichenoides. The descriptions and figures are excellent, and 

his notes on occasional lichen characteristics and on localities are full of 

interest. His lichen herbarium, which still exists at Oxford, mounted with 

the utmost care and neatness, has been critically examined by Nylander and 

Crombie 1 and many of the species identified. 

Dillenius was ignorant of, or rejected, Micheli's method of classification, 

adopting instead the form of the thallus as a guide to relationship. He also 

differed from him in his views as to propagation, regarding the soredia as 

the pollen of the lichen, and the apothecia as the seed-vessels, or even in 

certain .cases as young plants. 

Haller's 2 

Shortly after the publication of Dillenius' Historia, appeared 

Systematic and Descriptive list of plants indigenous to Switzerland. The 

lichens are described as without visible leaves or stamens but with "corpus- 

cula" instead of flowers and leaves. He arranged his lichen species, 160 in 

all, under seven different Orders: I. "Lichenes Corniculati and Pyxidati"; 

"L. Crustacei" 

2. "L. Coralloidei"; 3. "L. Fruticosi"; 4. "L. Pulmonarii"; 5. 

(with flower-shields); 6. "L. Scutellis" (with shields but with little or no 

thallus); and 7. "L. Crustacei" (without shields). 

This period extends till near the end of the eighteenth century, and 

thus includes within its scope the foundation of the binomial system of 

renowned Swedish botanist 

naming plants established by Linnaeus 3 The . 

rather scorned lichens as "rustici pauperrimi," happily translated by 

Schneider 4 as the "poor trash of vegetation," but he named and listed about 

80 species. He divided his solitary genus Lichen into sections: i. "Leprosi 

tuberculati"; 2. "Leprosi scutellati"; 3. "Imbricati"; 4. "Foliacei"; 


- Haller 1742. 

3 Linnaeus 1753. 

4 Schneider 1897.

8 


5. "Coriacei"; 6. "Scyphiferi"; 7. "Filamentosi." By this ordered sequence 

Linnaeus showed his appreciation 

of development, beginning, as he does, 

with the leprose crustaceous thallus and continuing up to the most highly 

organized filamentous forms. He and his followers still included the genus 

Lichen among Algae. 

A voluminous History of Plants had been published in 1751 by 

Sir John 

1 

Hill , the first superintendent 

to be appointed to the Royal 

lichens are included under the Class 

Gardens, Kew. In the History 

"Mosses," and are divided into several vaguely limited ''genera" Usriea, 

tree mosses, consisting of filaments only; Platysma, 

flat branched tree 

mosses, such as lungwort; Cladonia, the orchil and coralline mosses, such as 

Cladoniafurcata ; Pyxidium, the cup-mosses; and Placodium, the crustaceous, 

friable or gelatinous forms. A number of plants are somewhat obscurely 

described under each genus. Not only were these new Lichen genera sug- 

gested by him, but among his plants are such binomials as Usnea compressa, 

other lichens 

Platysmacorniculatum, Cladoniafurcata and Cladonia tophacea ; 

are trinomial or are indicated, in the way then customary, by a whole sentence. 

Hill's studies embraced a wide variety of subjects; he had flashes of 

insight, but not enough concentration to make an effective application of 

his ideas. In his Flora Britannica*, which was compiled after the publication 

of Linnaeus's Species Plantarum, he abandoned his own arrangement in 

favour of the one introduced by Linnaeus and accepted again the genus 

single 

Lichen. 

Sir William Watson 3 

, a London apothecary and physician of scientific 

repute at this period, proposed a rearrangement and some alteration of 

Linnaeus's sections. He had failed to grasp the principle of development, 

but he gives a good general account of the various groups. Watson was the 

progenitor of those who decry the makers and multipliers of species. So in 

regard to Micheli, who had increased the number to "298," he writes: "it is to 

be regretted, that so indefatigable an author, one whose genius particularly 

led him to scrutinize the minuter subjects of the science, should have been 

so solicitous to increase the number of species under all his genera: an error 

this, which tends to great confusion and embarassment and must retard the 

progress and real improvement of the botanic science." Linnaeus however 

in redressing the balance earned his full approbation: "He has so far 

retrenched the genus (Lichen} that in his general enumeration of plants he 

recounts only 80 species belonging to it." 

Linnaeus's binomial system was almost at once adopted by the whole 

botanical world and the discovery and tabulation of lichens as well as of 

other plants proceeded apace. Scopoli's 4 Flora Carniolica, for instance, 

published in 1760, still adhered to the old descriptive method of nomen- 

1 Hill i7 5 i. Hill'sgenus Collema is Nostoc, etc. 

2 Hill 1760. 

8 Watson 1759. 

4 Scopoli 1760.

PERIOD III. 1729-1780 t 9 

clature, but a second edition, issued twelve years later, is based on the new 

system : it includes 54 lichen species. 

About this time Adanson 1 

proposed a new classification of plants, 

dividing them into families, and these again into sections and genera. He 

transferred the lichens to the Family "Fungi," and one of his sections 

contains a number of lichen genera, the names of these being culled from 

previous workers, Dillenius, Hill, etc. A few new ones are added by himself, 

and one of them, Graphis, still ranks as a good genus. 

In England, Hudson 2 who was an apothecary and became sub-librarian 

, 

of the British Museum, followed Linnaeus both in the first and later editions 

of the Flora Anglica. He records 102 lichen species. Withering 3 w ras also 

engaged, about this time, in compiling his Arrangement of Plants. He 

translated Linnaeus's term "Algae" into the English word "Thongs," the 

lichens being designated as "Cupthongs." In later editions, he simply 

whose descriptive and economic notes 

classifies lichens as such. Lightfoot 4 

, 

are full of interest, records 103 lichens in the Flora Scotica, and Dickson 5 

shortly after published a number of species from Scotland, some of them 

hitherto undescribed. Dickson was a nurseryman who settled in London, 

and his avocations kept him in touch with plant-lovers and with travellers 

in many lands. 

E. PERIOD IV. 1780-1803 

The inevitable next advance was made by Weber 6 who at the time was 

a Professor at Kiel. In a first work dealing with lichens he had followed 

Linnaeus; then he published a new method of classification in which the 

lichens are considered as an independent Order of Cryptogamia, and that 

Order, called "Aspidoferae," he subdivided into genera. His ideas had been 

partly anticipated by Hill and by Adanson, but the work of Weber indicates 

a more correct view of the nature of lichens. He established eight fairly 

well-marked genera, viz. Verrucaria, Tubercularia, Sphaerocephalum and 

Placodium,vf\\ic\\ were based on fruit-characters, the thallus being crustaceous 

and rather insignificant, and a second group Lichen, Collema, Cladonia and 

Usnea, in which the thallus ranked first in importance. Though Weber's 

scheme was published in 1780, it did not at first secure much attention. 

The great authority of Linnaeus dominated so strongly the botany of the 

period that for a long time no change was welcomed or even tolerated. 

In our own country Relhan at Cambridge and Sibthorp 7 at Oxford 

were making extensive studies of plants. The latter was content to follow 

Linnaeus in -his treatment of lichens. Relhan 8 also grouped his lichens 

under one genus though, in a second edition of his Flora, he broke away 

from the Linnaean tradition and adopted the classification of Acharius. 

1 Adanson 1763. 

5 Dickson 1785. 

2 Hudson 1762 and 1778. 

6 Weber 1780. 

3 

Withering 1776. 

7 

Sibthorp 1794. 

* 

Lightfoot 1777. 

8 Relhan 1785 and 1820.

I0 


Extensive contributions to the knowledge of English plants generally 

were made by Sir 1 

James Edward Smith who, in 1788, founded the Linnean 

Society of London of which he was President until his death in 1828. He 

began his great work, English Botany, in 1790 with James Sowerby as 

artist. Smith's and Sowerby 's part of the work came to an end in 1814; 

Hooker who had the assistance of 

but a supplement was begun in 1831 by 

Sowerby's sons in preparing the drawings. Nearly all the lichens recorded 

by Smith are published simply as Lichen, and his Botany thus belongs to 

the period under discussion, though in time it stretches far beyond. 

Continental lichenologists had been more receptive to new ideas, and 

other genera were gradually added to Weber's list, notably by Hoffmann 2 

and Persoon 3 . 

For a long time little was known of the lichens of other than European 

countries. Buxbaum 4 in the East, Petiver 5 and Hans Sloarie 6 in the West 

made the first exotic records. The latter notes how frequently lichens grew 

on the imported Jesuit's bark, and he quaintly suggests in regard to some 

of these species that they may be identical with the "hyssop that springeth 

out of the wall." It was not however till towards the end of the eighteenth 

century that much attention was given to foreign lichens, when Swartz 7 in 

the West Indies and Desfontaines 8 in N. Africa collected and recorded 

a fair number. Swartz describes about twenty species 

collected on his 

journey through the West Indian Islands (1783-87). 

Interest was also growing in other aspects of lichenology. Georgi 9 

a , 

Russian Professor, was the first to make a chemical analysis of lichens. He 

experimented on some of the larger forms and extracted and examined the 

mucilaginous contents of Ramalina farinacea, Platystna glaucum, Lobaria 

pulmonaria, etc., which he collected from birch and pine trees. About this 

time also the French scientists Willomet 10 Amoreux and Hoffmann , 

jointly 

published theses setting forth the economic value of such lichens as were 

used in the arts, as food, or as medicine. 

F. PERIOD V. 1803-1846 

The fine constructive work of Acharius appropriately begins a new era 

in the history of lichenology. Previous writers had indeed included lichens 

in their survey of plants, but always as a somewhat side issue. Acharius 

made them a subject of special study, and by his scientific system of classification 

raised them to the rank of the other great classes of plants. 

Acharius was a country doctor at Wadstena on Lake Malar in Sweden, 

" 

as he himself calls it, the country of lichens." He was attracted to the 

1 Smith 1790. 

3 Hoffmann 1798. 

5 

Petiver 1712. 

6 

Sloane 1796 and 1807. 

9 

Georgi 1797. 

10 

Willomet, etc. 1787. 

8 Persoon 1794. 

7 Swartz 1788 and 1791. 

4 Buxbaum 1728. 

s Desfontaines 1798-1800.

PERIOD V. 1803-1846 ii 

study of them by their singular mode of growth and organization, both of 

thallus and reproductive organs, for which reason he finally judged that 

lichens should be considered as a distinct Order of Cryptogamia. 

In his first tentative work 1 he had followed his great compatriot 

Linnaeus, classifying all the species known to him under the one genus 

Lichen, though he had progressed so far as to divide the unwieldy Genus 

into Families and these again into Tribes, these latter having each a tribal 

designation such as Verrucaria, Opegrapha, etc. He established in all twentyeight 

tribes which, at a later stage, he transformed into genera after the 

example of Weber. 

Acharius, from the beginning of his work, had allowed great importance 

to the structure of the apothecia as a diagnostic character though scarcely 

recognizing them as true fruits. He gave expression to his more mature 

views first in the Methodus Lichenum*, then subsequently in the larger 

Lichenographia Universalia*. In the latter work there are forty-one genera 

arranged under different divisions; the species are given short and succinct 

descriptions, with habitat, locality and synonymy. No material alteration 

was made in the Synopsis Lichenum*, a more condensed work which he pub- 

lished a few years later. 

The Cryptogamia are divided by Acharius into six " Families," one of 

which, " Lichenes," is distinguished, he finds, by two methods of propagation : 

by propagula (soredia) and by spores produced in apothecia. He divides 

the family into classes characterized solely by fruit characters, and these 

again into orders, genera and species, of which diagnoses are given. With 

fuller knowledge many changes and rearrangements have been found 

necessary in the application and extension of the system, but that in no way 

detracts from the value of the work as a whole. 

' 

In addition to founding a scientific classification, Acharius invented 

a^lerminology for the structures peculiar to lichens. We owe to him the 

names and descriptions of " 

thallus," " 

podetium," " 

apothecium," " perithecium," 

"soredium," "cyphella" and "cephalodium," the last word however 

with a different meaning from the one now given to it. He proposed 

several others, some of which are redundant or have fallen into disuse, but 

many 

found of service in allied branches of botany. J\ 

of his terms as we see have stood thotest of time and have been 

Lichens were studied with great zest by the men of that day. Hue 5 

recalls a rather startling incident in this connection: Wahlberg, it is said, 

had informed Dufour that he had sent a large collection of lichens from 

Spain to Acharius who was so excited on receiving them, that he fell ill 

and died in a few days (Aug. Hth, 1819). Dufour, however, had added the 

comment that the illness and death might after all be merely a coincidence. 

1 Acharius 1798. 



4 Acharius 1814. Hue 1908.


Among contemporary botanists, we find that De Candolle 1 

in the volume 

he contributed to Lamarck's French Flora, quotes only from the earlier work 

of Acharius. He had probably not then seen the Methodus, as he uses none 

of the new terms ; the lichens of the volume are arranged under genera 

which are based more or less on the position of the apothecia on the thallus. 

Florke 2 

the , next writer of consequence, frankly accepts the terminology 

and the new view of classification, though differing on some minor points. 

Two lists of lichens, neither of particular note, were published at this 

time in our country: one by Hugh Davies 3 for Wales, which adheres to the 

Linnaean system, and the other by Forster 4 of lichens round Tonbridge. 

Though Forster adopts the genera of Acharius, he includes lichens among 

algae. A more important publication was S. F. Gray's 5 Natural Arrangement 

of British Plants. Gray, who was a druggist in Walsall and afterwards 

a lecturer on botany in London, was only nominally 6 the author, as it was 

mainly the work of his son John Edward Gray 7 sometime , Keeper of Zoology 

in the British Museum. Gray was the first to apply the principles of the 

Natural System of classification to British plants, but the work was opposed 

by British botanists of his day. The years following the French Revolution 

and the Napoleonic wars were full of bitter feeling and of prejudice, and 

anything emanating, as did the Natural System, from France was rejected 

as unworthy of consideration. 

In the Natural Arrangement, Gray followed Acharius in his treatment 

of lichens ; 

but whereas Acharius, though here and there confusing fungus 

species with lichens, had been clear-sighted enough to avoid all intermixture 

of fungus genera, with the exception of one only, the sterile genus Rhizo- 

morpha, Gray had allowed the interpolation of several, such as Hysterium, 

Xylaria, Hypoxylon, etc. He had also raised many of Acharius's subgenera 

and divisions to the rank of genera, thus largely increasing their number. 

This oversplitting of well-defined genera has somewhat weakened Gray's 

work and he has not received from later writers the attention he deserves. 

The lichens of Hooker's 8 Flora Scotica, which is synchronous with Gray's 

work, number 195 species, an increase of about 90 for Scotland since the 

publication of Lightfoot's Flora more than 40 years before. Hooker also 

followed Acharius in his classification of lichens both in the Flora Scotica 

and in the Supplement to English Botany*, which was undertaken by the 

younger Sowerbys and himself. To that work Borrer (1781-1862), a keen 

lichenologist, supplied many new and rare lichens collected mostly in Sussex. 

It is a matter of regret that Greville should have so entirely ignored 

lichens in his great work on Scottish Cryptogams. The two species of 

1 De Candolle 2 

1805. Florke 18x5-1819. Davies * 

1813. Forster 5 :8i6. S. F. Gray 1821. 

6 

7 

Carrington 1870. See List of the Books, etc. by John Edward Gray, 8 p. 3 1872 

Hooker 1821. Hooker " 

1831. 

Greville 1823-1827.

PERIOD V. 1803-1846 13 

Lichina are the only ones he figured, and these he took to be algae. He 1 was 

well acquainted with lichens, for in the Flora Edinensis he lists 128 species 

for the Edinburgh district, arranging the genera under "Lichenes" with the 

exception of Opegrapha and Verrucaria which are placed with the fungus 

" 

genus Poronia in Hypoxyla." Though he cites the publications of Acharius, 

he does not employ his scientific terms, possibly because he was writing his 

diagnoses in English. Two other British works of this time still remain to 

be chronicled : Hooker's 2 contributions to Smith's English Flora and 

Taylor's 3 work on lichens in Mackay's Flora Hibernica. Through these the 

knowledge of the subject was very largely extended in our country. 

The classification of lichens and their place in the vegetable kingdom 

were now firmly established on the lines laid down by Acharius. Fries 4 in 

his important work Lichenographia Europaea more or less followed his dis- 

tinguished countryman. The uncertainty as to the position and relationship 

of lichens had rendered the task of systematic arrangement one of peculiar 

difficulty and had unduly absorbed attention but now that a ; 

satisfactory 

order had been established in the chaos of forms, the way was clear for other 

aspects of the study. Several writers expressed their views by suggesting 

somewhat different methods of classification, others wrote monographs of 

separate groups, or genera. Fee 5 

published an Essay on the Cryptogams 

(mostly lichens) that grew on officinal exotic barks; Florke 8 took up the 

difficult genus Cladonia\ Wallroth 7 also wrote on Cladonia\ Delise 8 on Sticta, 

and Chevalier 9 

published a long and elaborate account of Graphideae. 

Wallroth and Meyer at this time published, simultaneously, important 

studies on the general morphology and physiology of lichens. Wallroth 10 

had contemplated an even larger work on the Natural History of Lichens, 

but only two of the volumes reached publication. In the first of these he 

devoted much attention to the " 

gonidia " or " brood-cells " and established 

the distinction between the heteromerous and homoiomerous distribution of 

green cells within the thallus; he also describes with great detail the "morphosis" 

and "metamorphosis" of the vegetative body. In the second volume 

he discusses their physiology the contents and products of the thallus, 

colouring, nutrition, season of development, etc. and finally the pathology 

of these organisms. He made no great use of the compound microscope, 

and his studies were confined to phenomena that could be observed with a 

single lens. 

Meyer's 11 work contains a still more exact study of the anatomy and 

physiology of lichens; he also devotes many passages to an account of their 

metamorphoses, pointing out that species alter so much in varying conditions, 

that the same one at different stages may be placed even in different genera; 

1 Greville 1824. 

- Hooker 1833. 

3 Taylor 1836. 

7 Wallroth 1829. 8 Delise 1822. Chevalier 1824. 

4 5 6 

Fries 1831. Fee 1874. Florke 1828. 

10 Wallroth " 

1825. Meyer 1825.

I4 


he however carries his theory of metamorphosis too far and unites together 

widely separated plants. Meyer was the first to describe the growth of the 

lichen from spores, though his description is somewhat confused. Possibly 

the honour of havingfirst observed their germination should be given to a later 

botanist, Holle 1 . The works of both Wallroth and Meyer enjoyed a great 

: and well-merited reputation they were standard books of consultation for 

2 

many years. Koerber who devoted a , long treatise to the study of gonidia, 

confirmed Wallroth's theories: he considered at that time that the gonidia 

in the soredial condition were organs of propagation. 

Mention should be made here of the many able and keen collectors who, 

in the latter half of the eighteenth century and the beginning of the nineteenth, 

did so much to further the knowledge of lichens in the British Isles. 

Among the earliest of these naturalists are Richard Pulteney (1730-1801), 

whose collection of plants, now in the herbarium of the British Museum, in- 

cludes many lichens, and Hugh Davies (1739-1821), a clergyman whose 

Welsh plants also form part of the Museum collection. The Rev. John 

Harriman (1760-1831) sent many rare plants from Egglestone in Durham 

to the editors of English Botany and among them were not a few lichens. 

Edward Forster (1765-1849) lived in Essex and collected in that county, 

more especially in and near Epping Forest, and another East country 

botanist, Dawson Turner (17/5-1858), though chiefly known as an algologist, 

gave considerable attention to lichens. In Scotland the two most active 

workers were Charles Lyell (1767-1849), of Kinnordy in Forfarshire, and 

George Don (1798-1 856), also a Forfar man. Don was a gardener and became 

eventually a foreman at the Chelsea Physic Garden. Sir Thomas Gage of 

Hengrave Hall (1781-1823) botanized chiefly in his own county of Suffolk ; 

but most of his lichens were collected in South Ireland and are incorporated in 

the herbarium of the British Museum. Miss Hutchins also collected in Ireland 

and sent her plants for inclusion in English Botany. But in later years, the 

principal lichenologist connected with that great undertaking was W. Borrer, 

who spent his life in Sussex : he not only supplied a large number of specimens 

to the authors, but he himself discovered and described many new lichens. 

American lichenologists were also extremely active all through this 

period. The comparatively few lichens of Michaux's 3 Flora grouped under 

" Lichenaceae " were collected in such widely separated regions as Carolina 

and Canada. A few years later Miihlenberg 4 included no fewer than 184 

species in his Catalogue of North American Plants. Torrey 6 and Halsey 6 

botanized over a limited area near New York, and the latter, who devoted 

himself more especially to lichens, succeeded in recording 176 different forms, 

old and new. These two botanists were both indebted for help in their work 

1 Holle 1849. 

4 

Muhlenberg 1813. 

2 Koerber 1839. 

5 

Torrey 1819. 

3 Michaux 1803. 

* Halsey 1824.

PERIOD V. 1803-1846 15 

to Schweinitz, a Moravian brother, who moved from one country to another, 

working and publishing, now in America and now in Europe. His name is 

however chiefly associated with fungi. Later American lichenology is 

nobly represented by Tuckerman 1 who issued his first work on lichens in 

1839, and who continued for many years to devote himself to the subject. 

He followed at first the classification and nomenclature that had been 

adopted by Fee, but as time went on he associated himself with all that was 

best and most enlightened in the growing science. 

Travellers and explorers in those days of high adventure were constantly 

sending their specimens to European botanists for examination and determination, 

and the knowledge of exotic lichens as of other classes of plants 

grew with opportunity. Among the principal home workers in foreign 

material, at this time, may be cited Fee 2 who described a very large series 

on officinal barks {Cinchona, etc.) so largely coming into use as medicines; 

he also took charge of the lichens in Martius's 3 Flora of Brazil. Montagne 4 

named large collections, notably those of Leprieur collected in Guiana, and 

Hooker 5 and Walker Arnott determined the plants collected during Captain 

Beechey's voyage, which included lichens from many different regions. 

G. PERIOD VI. 1846-1867 

The last work of importance, in which microscopic characters were 

ignored, was the Enumeratio critica Lichenum Europaeum by Schaerer 6 

veteran lichenologist, who rather sadly realized at the end the limitations 

of that work, as he asks the reader to accept it " such as it is." Many years 

previously, Eschweiler 7 in his Systema and Fee 8 in his account of Cryptogams 

on Officinal Bark, had given particular attention to the internal structure as 

well as to the outward form of the lichen fructification. Fe"e, more especially, 

had described and figured a large number of spores; but neither writer had 

done more than suggest their value as a guide in the determination of genera 

and species. 

9 

It was an Italian botanist, Giuseppe de Notaris a Professor in , Florence, 

who took up the work where Fee had left it. His comparative studies of both 

vegetative and reproductive organs convinced him of the great importance 

of spore characters in classification, the spore being, as he rightly decided, 

the highest and ultimate product of the lichen plant. In his microscopic 

examination of the various recognized genera, he found that while, in some 

genera, the spores conformed to one distinct type, in others their diversities 

in form, septation or colour gave a decisive reason for the establishment of 

new genera, while minor differences in size, etc. of the spores proved to be of 

great value in distinguishing species. The spore standard thus marks a new 

1 Tuckerman 1839. 

6 Schaerer 1850. 

2 s 4 

5 Fee 1824. Martius 1833. Montagne 1851. Hooker 1841. 

~ 

8 9 Eschweiler 1824. Fee 1824. De Notaris 1846. 

, 

a

16 


departure in lichenology. De Notaris published the results of his researches 

in a fragment of a projected larger work that was never completed. Though 

his views were overlooked for a time, they were at length fully recognized 

and further elaborated by Massalongo 1 in Italy, by Norman 2 in Norway, by 

Koerber 3 in Germany and by Mudd 4 in our own country. Massalongo had 

drawn up the scheme of a great Scolia Lichenographica, but like de Notaris, 

he was only able to publish a part. After twelve years of ill-health, in which 

he struggled to continue his work, he died at the early age of 36. 

Lindsay 5 Mudd and , Leighton 6 were at this time devoting great attention 

to British lichens. Lauder Lindsay's Popular History of British Lichens, 

with its coloured plates and its descriptive and economic account of these 

plants has enabled many to acquire a wide knowledge of the group. Mudd's 

Manual, a more complete and extremely valuable contribution to the subject, 

followed entirely on the lines of Massalongo's work. From his large 

in the examination of lichens he came to the conclusion that : 

experience 

" Of all organs furnished by a given group of plants, none offer so many 

real, constant and physiological characters as the spores of lichens, for the 

formation of a simple and natural classification." 

Meanwhile, a contemporary writer, William Nylander, was rising into 

fame. He was born at Uleaborg in Finland 7 in 1822 and became interested 

in lichens very early in his career. His first post was the professorship of 

botany at Helsingfors; but in 1863 he gave up his chair and removed to 

Paris where he remained, except for short absences, until his death. One 

of his excursions brought him to London in 1857 to examine Hooker's 

herbarium. He devoted his whole life to the study of lichens, and from 

1852, the date of his first lichen publication, which is an account of the lichens 

of Helsingfors, to the end of his life he poured out a constant succession of 

books or papers, most of them in Latin. One of his earliest works was an 

he elaborated later, but which in its main 

Essay on Classification 91 which 

features he never altered. He relied, in his system, on the structure and form 

of thallus, gonidia and fructifications, more especially on those of the 

spermogonia (pycnidia), but he rejected ascospore characters except so far as 

they were of use in the diagnosis of species. He failed by being too isolated 

and by his unwillingness to recognize results obtained by other workers. 

In 1866 he had discovered the staining reactions of potash and hypochlorite 

of lime on certain thalli, and though these are at times unreliable owing to 

growth conditions, etc., they have generally been of real service. Nylander, 

however, never admitted any criticism of his methods; his opinions once 

stated were never revised. He rejected absolutely the theory of the dual 

nature of lichens propounded by Schwendener without seriously examining 

1 

Massalongo 1852. Norman 1852. - 3 Koerber 1855. 

5 

Lindsay 1856. Leighton 1851, etc. 

7 See Hue 1899. 

4 Mudd 1861. 

8 

Nylander 1854 and 1855.

PERIOD VI. 1846-1867 17 

the question, and regarded as personal enemies those who dared to differ 

from him. The last years of his life were passed in complete solitude. He 

died in March 1899. 

Owing to the very inadequate powers of magnification at the service of 

scientific workers, the study of lichens as of other plants was for long restricted 

to the collecting, examining and classifying of specimens according to their 

macroscopic characters; the microscopic details observed were isolated and 

unreliable except to some extent for spore characters. Special interest is 

therefore attached to the various schemes of classification, as each new one 

proposed reflects to a large extent the condition of scientific knowledge of 

the time, and generally marks an advance. It was the improvement of the 

microscope from a scientific toy to an instrument of research that opened 

up new fields of observation and gave a new impetus to the study of a group 

of plants that had proved a puzzle from the earliest times. 

Tulasne was one of the pioneers in microscopic botany. He made 

a methodical study of a large series of lichens 1 and traced their development, 

so far as he was able, from the spore onwards. He gave special attention 

to the form and function of spermogonia and spermatia, and his work is 

enriched by beautiful figures of microscopic detail. Lauder Lindsay 2 also 

published an elaborate treatise on spermogonia, on their occurrence in the 

lichen kingdom and on their form and structure. The paper embodies the 

results of wide microscopic research and is a mine of information regarding 

these bodies. 

3 

Much interesting work was contributed at this time by Itzigsohn , 

Speerschneider 4 Sachs , 5 Thwaites , 6 and , 

others. They devoted their researches 

to some particular aspect of lichen development and their several contribu- 

tions are discussed elsewhere in this work. 

Schwendener 7 followed with a systematic study of the minute anatomy 

of many of the larger lichen genera. His work is extremely important in 

itself and still more so as it gradually revealed to him the composite 

character of the thallus. 

Several important monographs date from this period : Leighton 8 reviewed 

all the British " Angiocarpous " lichens with special reference to their 

" 

sporidia " 

though without treating these as of generic value. He followed 

up this monograph by two others, on the 9 

Graphideae and the Umbili- 

of the British Cladoniae. 

carieae, and Mudd 11 

published a careful study 

On the Continent Th. Fries 12 issued a revision of Stereocaulon and Pilo- 

pkoron and other writers contributed work on smaller groups. 

1 Tulasne 1852. 

5 

Sachs 1855. 

9 

Leighton 1854. 

2 Lauder Lindsay 1859. 

fi Thwaites 1849. 

10 


3 

Itzigsohn 1854-1855. 

4 

Speerschneider 1853. 

7 Schwendener 1863-1868. 

" Mudd 1865. 

8 


12 Th. Fries 1858.

I8 


H. PERIOD VII. 1867 AND AFTER 

1 

Modern lichenology begins with the enunciation of Schwendener's 

theory 

of the composite nature of the lichen plant. The puzzling resemblance of 

certain forms to algae, of others to fungi, had excited the interest of botanists 

from a very early date, and the similarity between the green cells in the 

thallus, and certain lower forms of algae had been again and again pointed 

out. Increasing observation concerning the life-histories of these algae and 

of the gonidia had eventually piled up so great a number of proofs of their 

identity that Schwendener's announcement must have seemed to many an 

inevitable conclusion, though no one before had hazarded the astounding 

statement that two organisms of independent origin were combined in the 

lichen. 

f The dual hypothesis, as it was termed, was not however universally 

accepted. It was indeed bitterly and scornfully rejected by some of the 

most prominent lichenologists of the time, including Nylander 2 

, J. Miiller 

and Crombie 3 . Schwendener held that the lichen was a fungus parasitic 

on an alga, and his opponents judged, indeed quite rightly, that such a view 

was wholly inadequate to explain the biology of lichens. It was not till a 

later datgjhat the truer conception of the "consortium" or "symbiosis" was 

proposed. ^T he researches undertaken to prove or disprove the new theories 

cojne under review in Chapter II. 

( Stahl's work on the development of the carpogonium in lichens gave a 

rte^direction to study, and notable work has beeadone during the last forty 

years in that as in other branches of lichenology./ 

Exploration of old and new fields furnished the lichen-flora of the world 

with many new plants which have been described by various systematists 

by Nylander, Babington, Arnold, Mujler, Th. Fries, Stizenberger, Leighton, 

Crombie and many others, and their contributions arc scattered through 

contemporary scientific journals. The number of recorded species is now 

somewhere about 40,00x3, though, in all probability, many of these will be 

found to be growth forms. Still, at the lowest computation, the number of 

different species is very large. 

Systematic literature has been enriched by a series of important mono- 

graphs, too numerous to mention here. While treating definite groups, they 

have helped to elucidate some of the peculiar biological problems of the 

symbiotic growth. 

Morphology, since Schwendener's time, has been well represented by 

Zukal, Reinke, Lindau, Funfstiick, Darbishire, Hue, and by an increasing 

number of modern writers whose work is duly acknowledged under each 

1 

Schwendener 1867. 

n- Nylander 1874. 

:i Croml.ie 1885.

PERIOD VII. 1867 AND AFTER 19 

subject of study. Hesse and Zopf, and more recently Lettau, have been 

engaged in the examination of those unique products, the lichen acids, while 

other workers have investigated lichen derivatives such as fats. Ecology of 

lichens has also been receiving increased attention. Problems of physiology, 

symbiosis, etc., are not yet considered to be solved and are being attacked 

from various sides. 

British lichenologists since 1867 have been mainly engaged on field 

work, with the exception of Lauder Lindsay who published after that date 

a second great paper on the spermogonia of crustaceous lichens. Leighton 

in his Lichen Flora and Crombie in numerous publications gave the lead in 

systematic work, and with them were associated a band of indefatigable 

collectors. Among these may be recalled Alexander Croall (1809-85), a 

parish schoolmaster in Scotland whose Plants of Braemar include many of 

the rarer mountain lichens. Henry Buchanan Holl (1820-86), a surgeon in 

London, collected in the Scottish Highlands as well as in England and 

Wales. William Joshua (1828-98) worked mostly in the Western counties 

of Somerset and Gloucestershire. Charles Du Bois Larbalestier, who died in 

191 1, was a keen observer and collector during many years; he discovered 

a number of new species in his native Jersey, in Cambridgeshire and also in 

Connemara; his plants were generally sent to Nylander to be determined 

and described. He issued two sets of lichens, one of Channel Island plants, 

the other of more general British distribution, and he had begun the issue 

of Cambridgeshire lichens. Isaac Carroll (1828-80), an Irish botanist, issued 

a first fascicle of Lichenes Hibernici containing 40 numbers. More recently 

Lett 1 has reported 80 species and varieties from the Mourn e Mountains in 

Ireland. Other more extensive sets were issued by Mudd and by Leighton, 

and later by Crombie and by Johnson. All these have been of great service 

to the study of lichenology in our country. Other collectors of note are 

Curnow (Cornwall), Martindale (Westmoreland), and E. M. Holmes whose 

valuable herbarium has been secured by University College, Nottingham. 

The publication of the volume dealing with Lichenes in Engier and 

Prantl's Pflanzenfamilien has proved a boon to all who are interested in the 

study 

of lichens. Fiinfstuck 2 

prepared the introduction, an admirable 

presentation of the morphological and physiological aspects of the subject, 

while Zahlbruckner 3 with , equal success, took charge of the section dealing 

with classification. 

1 Lett 1890. 

- Fiinfstiick 1898. 

:t Zahlbruckner 1903-1907.

CHAPTER II 


I. LICHEN GONIDIA 

THE thallus or vegetative body of lichens differs from that of other green 

plants in the sharp distinction both of form and colour between the assimilative 

cells and the colourless tissues, and in the relative positions these 

occupy within the thallus: in the greater number of lichen species the green 

chlorophyll cells are confined to a narrow zone or band some way beneath 

and parallel with the surface (Fig. i); in a minority of genera they are dis- 

tributed through the entire thallus (Fig. 2); 

Fig. i. Physcia aipolia Nyl. Vertical 

section of thallus. a, cortex; b, algal 

layer; c, medulla; d, lower cortex, 

x 100 (partly diagrammatic). 

but in all cases the tissues 

Fig. i. Collema ntgrescens Ach. Vertical 

section of thallus. , chains of the 

alga Nostoc ; b, fungal filaments, x 600. 

remain distinct. The green zone can be easily demonstrated in any of the 

larger lichens by scaling off the outer surface cells, or by making a vertical 

section through the thallus. The colourless cells penetrate to some extent 

among the green cells; they also form the whole of the cortical and 

medullary tissues. 

These two different elements we now know to consist of two distinct 

organisms, a fungus and an alga. The green algal cells were at one time 

considered to be reproductive bodies, and were called "gonidia," a term still 

in use though its significance has changed.

LICHEN GONIDIA 21 

i. GONIDIA IN RELATION TO THE THALLUS 

A. HISTORICAL ACCOUNT OF LICHEN GONIDIA 

There have been few subjects of botanical investigation that have 

roused so much speculation and such prolonged controversy as the question 

of these constituents of the lichen plant. The green cells and the colourless 

filaments which together form the vegetative structure are so markedly 

dissimilar, that constant attempts have been made to explain the problem 

of their origin and function, and thereby to establish satisfactorily the 

relationship of lichens to other members of the Plant Kingdom. 

In gelatinous lichens, represented by Collema, of which several species 

are common in damp places and grow on trees or walls or on the ground, 

the chains of green cells interspersed through the thallus have long been 

recognized as comparable with the filaments of Nostoc, a blue-green 

gelatinous alga, conspicuous in wet weather in the same localities as those 

inhabited by Collema. So among early systematists, we find Ventenat 1 

classifying the few lichens with which he was acquainted under algae and 

hazarding the statement that a gelatinous lichen such as Collema was only 

a Nostoc changed in form. Some years later Cassini 2 in an account of Nostoc 

expressed a somewhat similar view, though with a difference: he suggested 

that Nostoc was but a monstrous form of Collema, his argument being that, 

as the latter bore the fruit, it was the normal and perfect condition of 

the plant. A few years later Agardh 3 claimed to have observed the meta- 

morphosis of Nostoc up to the fertile stage of a lichen, Collema limosum. 

But long before this date, Scopoli 4 had demonstrated a green colouring 

substance in non-gelatinous lichens by rubbing a crustaceous or leprose 

thallus between the fingers; and Persoon 5 made use of this green colour 

characteristic of lichen crusts to differentiate these plants from fungi. 

Sprengel 6 went a step further in exactly describing the green tissue as 

forming a definite layer below the upper cortex of foliaceous lichens. 

The first clear description and delimitation of the different elements 

composing the lichen thallus was, however, given by Wallroth 7 . He 

drew 

attention to the great similarity between the colourless filaments of the 

lichen and the hyphae of fungi. The green globose cells in the chlorophyllaceous 

lichens he interpreted as brood-cells or gonidia, regarding them as 

organs of reproduction collected into a "stratum gonimon." To the same 

author we owe the terms "homoiomerous" and "heteromerous," which he 

coined to describe the arrangement of these green cells in the tissue of the 

thallus. In the former case the gonidia are distributed equally through the 

structure; in the latter they are confined to a distinct zone. 

1 Ventenat 1794, p. 36. 

5 Persoon 1794, p. 17. 

2 

Cassini 1817, p. 395. 

3 

Agardh 1820. 

4 

Scopoli 1/60, p. 79. 

6 

Sprengel 1804, p. 325. 

7 Wallroth 1825, I.

22 CONSTITUENTS OF THE LICHEN THALLUS 

Wallroth's terminology and his views of the. function of the gonidia were 

accepted as the true explanation for many years, the opinion that they were 

solely reproductive bodies being entirely in accordance with the well-known 

part played by soredia in the propagation of lichens and soredia always 

include one or more green cells. 

B. GONIDIA CONTRASTED WITH ALGAE 

In describing the gonidia of the Graphideae Wallroth 1 had pointed out 

their affinity with the filaments of Chroolepus ( Trentepohlid) umbrina. He 

considered these and other green algae when growing 10986 on the trunks of 

trees to be but "unfortunate brood-cells" which had become free and, though 

capable of growth and increase, were unable to form again a lichen plant. 

Further observations on gonidia were made by E. Fries 2 : he found that 

the green cells escaped from the lichen matrix and produced new individuals; 

and also that the whole thallus in moist localities might become dissolved 

into the alga known as Protococcus viridis\ but, he continues, "though these 

Protococcus cells multiplied exceedingly, they never could rise again to the 

perfect lichen." Kiitzing 3 

, in a later account of Protococcus viridis, also 

recognized its affinity with lichens; he stated that he could testify from 

observation that, according to the amount of moisture present, it would 

develop, either in excessive moisture to a filamentous alga, or in drier con- 

ditions "to lichens such as Lecanora subfusca or Xanthoria parietina." 

A British botanist, G. H. K. Thwaites 4 

, at one time -superintendent of 

the botanical garden at Peradeniya in Ceylon, published a notable paper 

on lichen gonidia in which he pointed out 

Fig. 3. Coenogomum ebeneum A. L. . . . . 

that as in Collema the green constituents 

of the thallus resembled the chains of Nostoc, 

so in the non-gelatinous lichens, the green 

globose cells were comparable or identical with 

Pleurococctis, and Thwaites further observed that 

they increased by division within the lichen 

thallus. He insisted too that in no instance were 

: gonidia reproductive organs they 

were essen- 

tial component parts of the vegetative body and 

necessary to the life of the plant. 

In a further 

paper on Chroolepus cbeneus Ag., a plant con- 

Sm. Tip ofiichen filament, the alga sisting of slender dark-coloured felted filaovergrown 

by dark fungal hyphae men ts, he described these filaments as being 

composed of a central strand which closely 

resembled the alga Chroolepus, and of a surrounding sheath of dark-coloured 

1 Wallroth 1825, 1, p. 303. 

3 

Kutzing 1843. 

, 

* Fries 1831, pp. Ivi and Ivii. 

4 Thwaites 1849, pp. 219 and 241.

LICHEN GONIDIA 

cells (Fig. 3): "occasionally," he writes, "the internal filament protrudes 

beyond the investing sheath, and may then be seen to consist of oblong 

cells containing the peculiar reddish oily-looking endochrome of Chroolepus? 

Thwaites placed this puzzling plant in a new genus, Cystocolens, at the same 

time pointing out its affinity with the lichen genus Coenogoninm. The 

plant is now known as Coenogonium 

ebeneum. Thwaites was on the 

threshold of the discovery as to the true nature of the relationship between 

the central filament and the investing sheath, but he failed to take the next 

forward step. 

Very shortly after, Von Flotow 1 

published his views on some other 

lichen gonidia. He had come to the conclusion that the various species of 

the alga, Gloeocapsa, so frequently found in damp places, among mosses and 

lichens, were merely growth stages of the gonidia of Ephebe pubescens, and 

bore the same relation to Ephebe as did Lepra viridis (Protococcus) to Par- 

melia. The gonidium of Ephebe is the gelatinous 

filamentous blue-green alga Stigonema (Fig. 4), 

and the separate cells are not unlike those of 

Gloeocapsa. Flotow had also demonstrated that the 

same type of gonidium was enclosed in the cepha- 

lodia of Stereocaulon. Sachs 2 

, tob, gave evidence as 

to the close connection between Nostoc and Col- 

lema. He had observed numerous small clumps of 

the alga growing in proximity to equally abundant 

thalli of Collema, with every stage of development 

represented from one to the other. He found cases 

where the gelatinous coils of Nostoc chains were 

penetrated by fine colourless filaments "as if invaded 

by a parasitic fungus." Later these threads were seen to be attached 

to some cell of the Nostoc trichome. Sachs concluded, however, from very 

careful examination at the time, that the colourless filaments were produced 

by the green cells. As growth proceeded, the coloured Nostoc chains became 

massed towards the upper surface, while the colourless filaments tended to 

occupy the lower part of the thallus. He calculated that during the summer 

season the metamorphosis from Nostoc to a fertile Collema thallus took from 

three to four months. He judged that in favourable conditions the change 

would inevitably take place, though if there should be too great moisture no 

Collema would be formed. His study of Cladonia was less successful as he 

mistook some colonies of Gloeocapsa for a growth condition of Cladonia 

gonidia, an error corrected later by Itzigsohn 3 . 

But before this date Itzigsohn 4 had published a paper setting forth his 

views on thallus formation, which marked a distinct advance. He did not 

1 Flotow 185^. 

- Sachs 1855. 

3 

Itzigsohn 1855. 

Fig. 4. Ephebe pubescens Nyl. 

Tip of lichen filament >: 600. 

4 Itzigsohn 1854.

24 


hazard any theory as to the origin of gonidia, but he had observed spermatia 

growing, much as did the cells of Oscillaria: by increase in length, and, by 

subsequent branching, filaments were formed which surrounded the green 

cells; these latter had meanwhile multiplied by repeated division till finally 

a complete thallus was built up, the filamentous tissue being derived from 

the spermatia, while the green layer came from the original gonidium. In 

contrasting the development with that of Collema, he represents Nostoc as 

a sterile product of a lichen and, like the gonidia of other lichens, only able 

to form a lichen thallus when it encounters the fructifying spermatia. 

Braxton Hicks 1 a , London doctor, some time later, made experiments 

with Chroococcus algae which grew in plenty on the bark of trees, and 

followed their development into a lichen thallus. He further claimed to 

have observed a C/ilorococcus, which was associated with a Cladonia, divide 

and form a Palmella stage. 

C. CULTURE EXPERIMENTS WITH THE LICHEN THALLUS 

It had been repeatedly stated that the gonidia might become independent 

of the thallus, but absolute proof was wanting until Speerschneider 2 

, 

who 

had turned his attention to the subject, made direct culture experiments 

and was able to follow the liberation of the green cells. He took a thinnish 

section of the thallus of Hagenia (Pkyscia) ciliaris, and, by keeping it moist, 

he was able to observe that the gonidial cells increased by division; the 

moist condition at the same time caused the colourless filaments to die 

away. This method of investigation was to lead to further results. It was 

resorted to by Famintzin and Baranetsky 3 who made cultures of gonidia 

extracted from three different lichens, Physcia (Xanthorid) parietina, 

Evernia furfuracea and Cladonia sp. They were able to observe the growth 

and division of the green cells and, in addition, the formation of zoospores. 

They recognized the development as entirely identical with that of the 

unicellular green alga, Cystococcus humicola Naeg. Baranetsky 4 continued 

the experiments and made cultures of the blue-green gonidia of Peltigera 

canina and of Collema pulposum. In both instances he succeeded in isolating 

them from the thallus and in growing them in moist air as separate 

organisms. He adds that "many forms reckoned as algae, may be considered 

as vegetating lichen gonidia such as Cystococcus, Polycoccus, Nostoc, 

etc." Meanwhile Itzigsohn 5 had further demonstrated by 

similar culture 

experiments that the gonidia of Peltigera canina corresponded with the 

algae known as Gloeocapsa monococca Kiitz., and as Polycoccus punctiformis 

Kiitz. 

1 Hicks 1860 and 1861. 

4 

Baranetsky 1869. 

2 

Speerschneider 1853. 

5 


= 

Famintzin and Baranetsky 1867.


D. .THEORIES AS TO THE ORIGIN OF GONIDIA 

Though the relationship between the gonidia within the thallus and free- 

living algal organisms seemed to be proved beyond dispute, the manner in 

which gonidia first originated had not yet been discovered. Bayrhoffer 1 

attacked this problem in a study of foliose and other lichens. According 

to his observations, certain colourless cells or filaments, belonging to the 

"gonimic" layer, grew in a downward direction and formed at their tips a 

faintly yellowish-green cell ; it gradually enlarged and was at length thrown 

off as a free globose gonidium, which represented the female cell. Other 

filaments from the "lower fibrous layer" of the thallus at the same time grew 

upwards and from them were given off somewhat similar gonidia which 

functioned as male cells. His observations and deductions, were fanciful, 

but it must be remembered that the attachment between hypha and alga 

in lichens is in many cases so close as to appear genetic, and also it often 

happens that as the gonidium multiplies it becomes free from the hypha. 

In his Meuioire sur les Lichens, Tulasne 2 described the colourless 

filaments as being fungal in appearance. The green cells he recognized as 

organs of nutrition, and once and again in his paper he states that they 

arose directly by a sort of budding process from the medullary or cortical- 

filaments, either laterally or at the apex. This apparently reasonable view 

of their origin was confirmed by other writers on the subject: by Speer- 

schneider 3 in his account of the anatomy of Usnea barbata, by de Bary 4 

and by Schwendener 5 in their earlier writings. But even while de Bary 

6 

he noted 

accepted the hyphal origin of the gonidia, that, accompanying 

Opegrapha atra and other Graphideae, on the bark were to be found free 

Chroolepus cells similar to the gonidia in the lichen thallus. He added that 

gonidia of certain other lichens in no way differed from Protococcus cells; 

and as for the gelatinous lichens he declared that "either they were the 

perfect fruiting form of Nostocaceae and Chroococcaceae hitherto looked 

on as algae or that these same Nostocaceae and Chroococcaceae are algbe 

which take the form of Col/etna, Ephebe, etc., when attacked by an ascomy- 

cetous fungus." 

All these investigators, and other lichenologists such as Nylander 7 

regarded the free-living organisms identified by them as similar to the green 

cells of the thallus, as only lichen gonidia escaped from the matrix and 

vegetating in an independent condition. 

The old controversy has in recent years been unexpectedly reopened by 

Elfving 8 who has sought again to prove the genetic origin of the green cells. 

His method has been to examine a large series of lichens by making 

sections of the growing areas, and he claims to have observed in every case 

1 

2 ;! 

4 

Bayrhoffer 1851. Tulasne 1852. Speerschneider 1854. de Bary 1866, p. 242. 

~ 

* 6 

8 Schwendener 1860, p. 125. deBary 1866, p. 291. Nylander 1870. Elfving 1903 and 1913. 

, 

still 

,


the hyphal origin of the gonidia: not only of Cystococcus but also of Trentepotdia, 

Stigonema and Nostoc. In the case of Cystococcus, the gonidium, he 

says, arises by the swelling of the terminal cell of the hypha to a globose 

form, and by the gradual transformation of the contents to a chlrophyll- 

green colour, with power of assimilation. In the case of filamentous gonidia 

such as Trentepohlia, the hyphal cells destined to become gonidia are 

intercalary. In Peltigera the cells of the meristematic plectenchyma become 

transformed to blue-green Nostoc cells. 

the 

A study was also made by him of the formation of cephalodia 1 

gonidia of which differ from those of the " host" thallus. In Peltigera aphtkosa 

he claims to have traced the development of these bodies to the branching 

and mingling of the external hairs which, in the end, form a ball of interwoven 

hyphae. The central cells of the ball are then gradually differentiated 

into Nostoc cells, which increase to form the familiar chains. Elfving allows 

that the gonidia mainly increase by division within the thallus, and that they 

also may escape and live as free organisms. His views are unsupported by 

direct culture experiments which are the real proof of the composite nature 

of the thallus. 

E. MlCROGONlDIA 

Another attempt to establish a genetic origin for lichen gonidia was made 

had found in his examination of Leptogium myochroum that 

by Minks 2 . He 

the protoplasmic contents of the hyphae broke up into a regular series of 

globular corpuscles which had a greenish appearance. These minute bodies, 

called by him microgonidia, were, he states, at first few in number, but 

gradually they increased and were eventually set free by the mucilaginous 

degeneration of the cell wall. As free thalline gonidia, they increased in 

size and rapidly multiplied by division. Minks was at first enthusiastically 

supported by Miiller 3 who had found from his own observations that micro- 

goiiidia might be present in any of the lichen hyphae and in any part of 

thf thallus, even in the germinating tube of the lichen spore, and was in that 

case most easily seen when the spores germinated within the ascus. He 

argued that as spores originated within the ascus, so microgonidia were 

developed within the hyphae. Minks's theories were however not generally 

accepted and were at last wholly discredited by Zukal 4 who was able to 

prove that the greenish bodies were contracted portions of protoplasm in 

hyphae that suffered from a lowered supply of moisture, the green colour 

not being due to any colouring substance, but to light effect on the pro- 

teins an outcome of special conditions in the vegetative life of the plant. 

Darbishire 5 criticized Minks's whole work with great care and he has arrived 

at the conclusion that the microgonidium may be dismissed as a totally 

mistaken conception. 

1 See p. .33. 

- Minks 1878 and 1879. 

3 Muller 1878 and 1884. 

4 Zukal 1884. 

5 Darbishire 1895!. 

,


F. COMPOSITE NATURE OF THALLUS 

Schwendener 1 meanwhile was engaged on his study of lichen anatomy. 

Though at first he adhered to the then accepted view of the genetic connection 

between hyphae and gonidia, his continued examination of the 

vegetative development led him to publish a short paper 2 in which he 

announced his opinion that the various blue-green and green gonidia were 

really algae and that the complete lichen in all cases represented a fungus 

living parasitically on an alga: in Ephebe, for example, the alga was a form 

of Stigonema, in the Collemaceae it was a species of Nostoc. In those lichens 

enclosing bright green cells, the gonidia were identical with Cystococcus 

humicola, while in Graphideae the brightly coloured filamentous cells were 

those of Chroolepus (Trentepohlia). This statement he repeated in an 

appendix to the larger work on lichens 3 and again in the following year 4 

when he described more fully the different gonidial algae and the changes 

produced in their structure and habit by the action of the parasite: "though 

eventually the alga is destroyed," he writes, "it is at first excited to more 

vigorous growth by contact with the fungus, and in the course of generations 

may become changed beyond recognition both in size and form." In support 

of his theory of the composite constitution of the thallus, Schwendener 

pointed out the wide distribution and frequent occurrence in nature of the 

algae that become transformed to lichen gonidia. He claimed as further 

proof of the presence of two distinct organisms that, while the colourless 

filaments react in the same way as fungi on the application of iodine, the 

gonidia take the stain of algal membranes. 

G. SYNTHETIC CULTURES 

Schwendener's "dual hypothesis," as it was termed, excited great interest 

and no little controversy, the reasons for and against being debated with 

considerable heat. Rees 5 was the first who attempted to put the matte*. to 

the proof by making synthetic cultures. For this purpose he took spores 

from the apothecium of a Collema and sowed them on pure cultures of Nostoc, 

and as a result obtained the formation of a lichen thallus, though he did not 

succeed in producing any fructification. He observed further that the 

hyphal filaments from the germinating spore died off when no Nostoc was 

forthcoming. 

Bornet 6 followed with his record of successful cultures. He selected for 

experiment the spores of PJiyscia (Xanthoria) parietina and was able to 

show that hyphae produced from the germinating spore adhered to the free- 

1 Schwendener 1860, etc. 

4 Schwendener 1869. 


5 Rees 1871. 

3 Schwendener 1868, p. 195. 

6 Bornet 1872.


growing cells of Protococcus 1 viridis and formed the early stages of a lichen 

thallus. Woronin 2 contributed his observations on the gonidia of Parmelia 

(Physcid) pulverulenta which he isolated from the thallus and cultivated in 

pure water. He confirmed the occurrence of cell division in the gonidia and 

also the formation of zoospores, these again forming new colonies of algae 

identical in all respects with the thalline gonidia. He was able to see the 

germinating tube from a lichen spore attach itself to a gonidium, though he 

failed in his attempts to induce further growth. In our own country Archer 3 

welcomed the new views on lichens, and attempted cultures but with very 

4 

little success. Further synthetic cultures were made by Bornet Treub , 5 and 

Borzi 6 with a series of lichen spores. They also were able to observe the 

first stages of the thallus. Borzi observed spores of Physcia (Xanthorid) 

parietina scattered among Protococcus cells on the branch of a tree. The 

spores had germinated and the first branching hyphae had already begun to 

encircle the algae. 

Additional evidence in favour of the theory of the independent origin of 

the colourless filaments and the green cells was furnished by Stahl's 7 re- 

search on hymenial gonidia in Endocarpon (Fig. 5). By making synthetic 

Endocarpon pusillum 

edw. Asci and spores, 

with hymenial gonidia x 

320 (after Stahl). 

Fig. 6. Endocarpon pusillum Hedw. Spore 

germinating in contact with hymenial 

gonidia x 320 (after Stahl). 

1 The authors quoted have been followed in their designation of the various green algae that form 

lichen gonidia. It is however now recognized ( Wille 1913) that either Protococcus viridis Ag. , Chlorella 

or other Protococcaceae may form the universal green coating on trees, etc., and be incorporated as 

lichen gonidia. Pleurococcus vulgaris Naeg. and Pleurococcus Naegeli Chod. are synonyms of Proto- 

coccus virtdis. In that alga there is no pyrenoid, and no zoospores are formed. 

The genus Cystococcus, according to Chodat ( 1913), is characterized by the presence of a pyrenoid 

and by reproduction with zoospores and is identical with Pleurococcus z^fcawMenegh. (non Naeg.), 

though Wille regards Meneghini's species as of mixed content. Paulson and Hastings (1920) now 

find that Chodat's pyrenoid is the nucleus of the cell. 

Woronin ,8 7 a. Archer ,873, ,874, 1875. Bornet r8 73 and 1874. 

'Treub ,873. 'Borzi ,875. 7 Stahl lg


cultures of the mature spores with these bodies, he was able to observe not 

only the germination of the spores and the attachment of the filaments to 

the gonidia (Fig. 6), but also the gradual building up of a complete lichen 

thallus to the formation of perithecia and spores. 

Some years later Bonnier 1 made an interesting series of synthetic cultures 

between the spores of lichens germinated in carefully sterilized conditions, 

and algae taken from the open (Figs. 7 and 8). Separate control cultures of 

Fig. 7. Germination of spore of Physcia parietitia De Not. in 

contact with Protococcus viridis Ag. x 950 (after Hornet). 

Fig. 8. Physcia parietitia De Not. Vertical section of thallus 

obtained by synthetic culture x 130 (after Bonnier). 

spores and algae were carried on at the same time, with the result that in 

one case lichen hyphae alone, in the other algae were produced. The various 

lichen spores with which he experimented were sown in association with the 

following algae: 

(i) PROTOCOCCUS. 

Pure synthetic cultures of Physcia (Xanthoria) parietina were begun in 

August 1884 on fragments of bark. In October 1886 the thallus was several 

centimetres in diameter, and some of the lobes were fruited. 

Physcia stellaris was also grown on bark; 

apothecia were developed. 

1 Bonnier 1886 and 1889. 

in one case both thallus and

3o CONSTITUENTS OF THE LICHEN THALLUS 

Parmelia acetabulum, another corticolous species, formed only a minute 

thallus about 5 mm. in diameter, but entirely identical with normally growing 

specimens. 

(2) PLEUROCOCCUS. 

Lecanora (Rinodina) sophodes, sown on rock in 1883, reached in 1886 a 

diameter of 13 mm. with fully developed apothecia. 

Lecanora ferruginea and L. subfusca after three years' culture formed 

sterile thalli only. 

Lecanora coilocarpa in four years, and L. caesio-rufa in three years formed 

very small thalli without fructification. 

(3) TRENTEPOHLIA (Chroolepus). 

Opegrapha vulgata in two years had developed thallus and apothecia. 

The control culture of the spores formed, as in nature, a considerable felt of 

mycelium in the interstices of the bark, but no pycnidia or apothecia. 

Graphis elegans. Only the beginning of a differentiated thallus was 

obtained with this species. 

T 

Verrucaria muralis (?) gave in less than a year a completely developed 

thallus. 

Bonnier also attempted cultures with species of Collema and Ephebe, but 

was unsuccessful in inducing the formation of a lichen plant. 

H. HYMENIAL GONIDIA 

Reference has already been made to the minute green cells which were 

originally described by Nylander- as occurring in the perithecia of a few 

Fyrenolichens as free gonidia, i.e. unentangled with lichen hyphae. Fuisting 3 

found them in the perithecium of Polyblastia (Staurothele) catalepta at a very 

early stage of its development when the perithecial tissues were newly 

differentiated from those of the surrounding thallus. The gonidia enclosed 

in the perithecium differed in no wise from those of the thallus: they had 

become mechanically enclosed in the new tissue; and while those in the 

outer compact layers died off, those in the centre of the structure, where a 

hollow space arises, were subject to very active division, becoming smaller 

in the process and finally filling the cavity. Winter's 4 researches on similar 

lichens confirmed Fuisting's conclusions: he described them as similar to 

the thalline gonidia but- lighter in colour and of smaller size, measuring 

frequently only 2-3 ^ in diameter, though this size increased to about 7 yu, 

when cultivated outside the perithecium. 

Stahl 5 

sufficiently demonstrated the importance of these gonidia in 

1 Bonnier was probably experimenting with an Arthopyrenia. Verrucaria species combine with 

Protococcus or according to Chodat with Coccobotrys gen. nov. 

2 Nylander [858. 

* 

Fuisting 1868, p. 674. 

* Winter 1876, p. 264. 

5 Stahl 1877.


supplying the germinating spores with the necessary algae. They come to 

assume an 

lie in vertical rows between the asci and, owing to pressure, 

elongate 

1 form (Figs. 5 and 6). They have been seen in very few lichens, in 

Endocarpon and Staurothele, both rather small genera of Pyrenolichens,and,so 

far as is known, in two Discolichens, Lecidea pkylliscocarpa and L.phyllocaris, 

2 

the latter recorded from Brazil by Wainio , and, on account of the inclusion 

of gonidia in the hymenium, placed by him in a section, Gonothecium, 

I. NATURE OF ASSOCIATION BETWEEN ALGA AND FUNGUS 

a. CONSORTIUM AND SYMBIOSIS. These cultures had established con- 

vincingly the composite nature of the lichen thallus, and Schwendener's 

opinion, that the relationship between the two organisms was some 

varying degree of parasitism, was at first unhesitatingly accepted by most 

botanists. Reinke 3 was the first to point out the insufficiency of this view 

to explain the long continued healthy life of both constituents, a condition 

so different from all known instances of the disturbing or fatal parasitism of 

one individual on another. He recognized in the association a state of 

mutual growth and interdependence, that had resulted in the production 

of an entirely new type of plant, and he suggested Consortium as a truer 

description of the connection between the fungus and the alga. 

had originally been coined by his friend Grisebach in a paper 3 

This term 

describing 

the presence of actively growing Nostoc algae in healthy Gunnera stems; 

and Reinke compared that apparently harmless association with the similar 

phenomenon in the lichen thallus. The comparison was emphasized by him 

in a later paper 4 on the same subject, in which he ascribes to each "consort" 

its function in the composite plant, and declares that if such a mutual life 

of Alga and Ascomycete is to be regarded as one of parasitism, it must be 

considered as reciprocal parasitism; and he insists that "much more 

appropriate for this form of organic life is the conception and title of Con- 

sortium" In a special work on lichens, Reinke 5 further elaborated his theory 

of the physiological activity and mutual service of the two organisms forming 

the consortium. 

Frank H 

suggested the term Homobium as appropriate, but it' is faulty 

inasmuch as it expresses a relationship of complete interdependence, and 

it has been proved that the fungus partly, and the alga entirely, have the 

power of free growth. 

A wider currency was given to this view of a mutually advantageous 

growth by de Bary 7 . He followed Reinke in refusing to accept as satisfactory 

the theory of simple parasitism, and adduced the evident healthy life of the 

algal cells the alleged victims of the fungus as incompatible with the 

1 See p. 62. 

4 Reinke 187.^. 

2 Wainio 1890, 2, p. 29. 

:! 

Reinke 1872, p. 108. 

5 Reinke 1873'-, p. 98. 

6 Frank 1876. 

7 de Bary 1879.

3 2 CONSTITUENTS OF THE LICHEN THALLUS 

parasitic condition. He proposed the happily descriptive designation 

of a 

Symbiosis or conjoint life which was mostly though not always, nor in equal 

degree, beneficial to each of the partners or symbionts. 

b. DIFFERENT FORMS OF ASSOCIATION. The type of association be- 

varies in different lichens. Bornet 1 

tween the two symbionts 

the development of the thallus in certain members of the Collemaceae, 

found that though as a rule the two elements of the thallus, as in some 

, in describing 

species of Collema itself, persisted intact side by side, there was in other 

members of the genus an occasional parasitism: 

short branches from the 

to some cell of the Nostoc 

main hyphae applied themselves by their tips 

chain (Fig. 9). The cell thus seized upon began to increase in size, and the 

Fig. 9. Pkysma chalazanum Arn. Cells of Nostoc chains penetrated 

and enlarged by hyphae x 950 (after Bomet). 

plasma became granular and gathered at the side furthest away from the 

point of attachment. Finally the contents were used up, and nothing was 

left but an empty membrane adhering to the fungus hypha. In another 

species the hypha penetrated the cell. These instances of parasitism are 

most readily seen towards the edge of the thallus where growth is more 

active; towards the centre the attached cells have become absorbed, and 

only the shortened broken chains attest their disappearance. The other 

cells of the chains remain uninjured. 

In Synalissa, a small shrubby gelatinous genus, the hypha, as described 

by Bornet and by Hedlund 2 , pierces the outer wall of the gelatinous alga 

(Gloeocapsd) and swells inside to a somewhat globose 

haustorium which 

rests in a depression of the plasma (Fig. 10). The alga, though evidently 

Bornet 1873. 

2 Hedlund 1892.

LICHEN GONIDIA 

undamaged, is excited to a division which takes place on a plane that passes 

through the haustorium; the two daughter-cells then separate, and in so 

doing free themselves from the hypha. 

Hedlund followed the process of association between the two organisms 

in the lichens Micarea (Biatorina) prasina and 

M. denigrata {Biatorina synothea), crustaceous 

species which inhabit trunks of trees or palings. 

In these the alga, one of the Chlorophyceae, has 

assumed the character of a Gloeocapsa but on 

cultivation it was found to belong to the genus 

Gloeocystis. The cells are globose and rather 

small ; they increase by the division of the contents 

into two or at most four portions which 

become rounded off and covered with a membrane 

before they become free from the mothercell. 

The lichen hypha, on contact with any one 

of the green cells, bores through the outer membrane and swells within to a 

haustorium, as in the gonidia of Synalissa. 

Fig. 10. Synalissa symphorea Nyl. 

Algae (Gloeocapsa) with hyphae 

from the internal thallus x 480 

(after Hornet). 

Penetrating haustoria were demonstrated by Peirce 1 in his study of the 

gonidia of Ramalina reticulata. In the first stage the tip of a hypha had 

pierced the outer wall of the alga, causing the protoplasm to contract away 

from the point of contact (Fig. 11). More advanced stages showed the 

extension of the haustorium into the centre of the cell, and, finally, the 

1 1 . 

Fig. Gonidia from Ramalina reticulata 

Nyl. A,gonidium pierced and cell contents 

shrinking x 560 ; B, older stage, 

the contents of gonidium exhausted x 900 

(after Peirce). 

Fig. 12. Pertusaria globultfera Nyl. Fungus 

and gonidia from gonidial zone x 500 

(after Darbishire). 

complete disappearance of the contents. In many cases it was found that 

penetration equally with clasping of the alga by the filament sets up an 

irritation which induces cell-division, and the alga, as in Synalissa, thus 

becomes free from the fungus. Hue 2 has recorded instances of penetration 

in an Antarctic species, Physcia puncticulata. It is easy, he says, to see the tips 

of the hyphae pierce the sheath of the gonidium and penetrate to the nucleus. 


z Hue 1915. 

S.L 3

34 


Lindau 1 has described the association between fungus and alga in 

Pertusaria and other crustaceous forms as one of contact only (Fig. 12). 

He found that the cell-membrane of the two adhering organisms was unbroken. 

Occasionally the algal cell showed a slight indentation, but was 

otherwise unchanged. The hyphal branch was somewhat swollen at the tip 

where it 'touched the alga, and the wall was slightly thinner. The attachment 

between the two cells was so close, however, that pressure on the cover- 

glass failed to separate them. 

Generally the hypha simply surrounds the gonidium with clasping 

branches. Many algae also lie free in the gonidial zone, and Peirce 2 claims 

that these are larger, more deeply coloured and in every way healthier 

looking than those in the grasp of the fungus. He ignores, however, the case 

of the soredial algae which though very closely invested by the fungus are 

yet entirely healthy, since on their future increase depends in many cases 

the reproduction of new individual lichens. 

In a recent study of a crustaceous sandstone lichen, " 

Caloplaca pyracea" 

Claassen 3 has sought to prove a case of pure parasitism. The rock was at first 

covered with the green cells of Cystococcus sp. Later there appeared greyish- 

white patches on the green, representing the invasion of the lichen fungus. 

These patches increased centrifugally, leaving in time a bare patch in the 

centre of growth which was again colonized by the green alga. The lichen 

fruited abundantly, but wherever it encroached the green cells were more 

or less destroyed. The true explanation seems to be that the green cells 

were absorbed into the lichen thallus, though enough of them persisted to 

start new colonies on any bare piece of the stone. In the same way large 

patches of Trentepohlia aurea have been observed to be gradually invaded 

by the dark coloured hyphae of Coenogonium ebeneum. In time the whole of 

the is alga absorbed and nothing is to be seen but the dark felted lichen. 

The free alga as such disappears, but it is hardly correct to describe the 

process as one of destruction. 

This algal genus Trentepohlia (Chroolepus) forms the gonidia of the 

Graphideae, Roccelleae, etc. It is a filamentous aerial alga which increases 

by apical growth. In the Graphideae, many of which grow on trees beneath 

the outer bark (hypophloeodal), the association between the two symbionts 

may be of the simplest character, but was considered by Frank 4 to be of an 

advanced type. According to his observations and to those of Lindau 5 , the 

fungal hyphae penetrate first between the cells of the periderm. The alga, 

frequently Trentepohlia nmbrina, tends to grow down into any cracks of the 

surface. It goes more deeply in when preceded by the hyphae. In some 

species both organisms maintain their independent growth, though each 

shows increased vigour when it conies into contact with the other. In some 

1 Lindau 1895'. 

* Peirce I899


instances the cells of the alga are clasped by the fungus which causes the 

disintegration of the filament. The cells lose their bright yellow or reddish 

colour and are changed in appearance to greenish lichen gonidia; but no 

penetration by haustoria has ever been observed in Trentepohlia. 

Bachmann's 1 

study of a similar gonidium in a calcicolous species of 

Opegrapha confirms Frank's results. The algae had pierced not only between 

the looser lime granules but also through a crystal of calcium carbonate, and 

occupied nests scooped out in the rock by means of acid formed and excreted 

by their filaments. When association took place with the fungus, the algal 

cells were more restricted to a gonidial zone; but some of the cells, having 

been pushed aside by the hyphae, had started new centres of gonidia. On 

contact with the hyphae there was a tendency to bud out in a yeast-like 

growth. 

In the thallus of the Roccelleae, the algal filament, also a Trentepohlia, is 

broken up into separate cells, but in the Coenogoniaceae, whether the 

gonidium be a Cladophora as in Racodium,or a Trentepohlia as in Coenogonium, 

the filaments remain intact and are invested more or less closely by the 

hyphae. 

A somewhat different type of association takes place between alga and 

fungus in Strigula complanata, an epiphyllous lichen more or less common 

2 

in tropical regions. Cunningham who found it near , 

Calcutta, described the 

algal constituent and placed it in a new genus, Mycoidea (Cephaleuros). It 

forms small plate-like expansions on the surface of the leaf, and also pene- 

trates below the cuticle, burrowing between that and the epidermal cells; 

occasionally, as observed by Cunningham, rhizoid-like growths pierce deeper 

into the tissue into and below the epidermal layer. Very frequently, in the 

wet season, a fungus takes possession of 

the alga and slender colourless hyphae 

creep along its surface by the side of the 

cell rows, sending out branches which 

grow downwards. Marshall Ward 3 described 

the same lichen from Ceylon. He 

states that the alga may be attacked at 

any stage, and if it is in a very young condition 

it is killed by the fungus; at a Fg- '3- Outer edge of Phycopeltis expansa 

. . Term., the alga attacked by hyphae and 

more advanced period of growth it COnpassing 

into separate gonidia x 500 (after 

tinues to develop as an integral part of Vaughan Jennings), 

the lichen thallus, but with more frequently divided and smaller cells. 

Vaughan Jennings 4 observed Strigula complanata in New Zealand associated 

with a closely allied chroolepoid alga Phycopeltis expansa. He also noted the 

growth of the fungus over the alga breaking up the plates of tissue and 

1 Bachmann 1913. 

2 

Cunningham 1879. 

3 Ward 1884. 

4 

Jennings 1895. 

32

36 


separating the cells which, from yellow, change to a green colour and 

become rounded off (Fig. 13). The mature lichen, a white thallus dotted 

with black fruits, contrasts strikingly with the yellow membranous alga. 

Lichen formation usually begins near the edge of the leaf and the margin of 

the thallus itself is marked by a green zone showing where the fungus has 

recently come into contact with the alga. 

More recently Hans Fitting 1 has described " Mycoidea parasitica" as it 

occurs on evergreen leaves in Java. The alga, a species of Cephaleuros, 

though at first an epiphyte, becomes partially parasitic at maturity. It penetrates 

below the cuticle to the outer epidermal cells and may even reach 

the tissue below. When it is joined by the lichen fungus, both constituents 

grow together to form the lichen. Fitting adds that the leaf is evidently but 

little injured. In this lichen the alga in the grip of the fungus loses its 

independence and may be killed off: it is an instance of something like 

intermittent parasitism. 

J. RECENT VIEWS ON SYMBIOSIS AND PARASITISM 

No hyphal penetration of the bright-green algal cell by means of 

haustoria had been observed by the earlier workers, Bornet 2 Bonnier , 3 and 

others, though they followed Schwendener 4 in regarding the relationship as 

one of host and parasite. Lindau, also, after long study accepted parasitism 

as the only adequate explanation of the associated growth, though he never 

found the fungus actually preying on the alga. 

In recent years interest in the subject has been revived by the researches 

of Elenkin 5 

a Russian , botanist who claims to have established a case for 

parasitism or rather "endosaprophytism." He has demonstrated by means 

of staining reagents the presence in the thallus of large numbers of dead 

algal cells. A few empty membranes are to be found in the cortex and in 

the gonidial zone, but the larger proportion occur below the gonidial zone 

and partly in the medulla. He describes the lower layer as a "necral" or 

"hyponecral" zone, and he considers that the hyphae draw their nourishment 

chiefly from dead algal material. The fungus must therefore be regarded in 

this case as a saprophyte rather than a parasite. The algae, he considers, 

may have perished from want of sufficient light and air or they may have 

been destroyed by an enzyme produced by the fungus. The latter he thinks 

is the more probable, as dead cells are frequently present among the living 

algae of the gonidial zone. To the action of the enzyme he also attributes 

the angular deformed appearance of many gonidia and the paler colour and 

gradual disintegration of their contents which are finally used up as endo- 

saprophytic nourishment by the fungus. Dead algal cells were more easily 

1 

Fitting 1910. 

2 Bornet 1873. 

3 Bonnier i88 9 2 . 

5 Elenkin 1903! and 1904!, 19042. 

4 Schwendener 1867.


seen, he tells us, in crustaceous lichens associated with " Pleurococcus" or 

" Cystococcus" \ they were much less frequent in the larger foliose or fruticose 

lichens. Dead cells of Trentepohlia were also difficult to find. 

In a second paper Elenkin records one clear instance of a haustorium 

entering an algal cell, and says he found some evidence of hyphal branches 

penetrating otherwise uninjured gonidia, round holes being visible in their 

outer wall, but he holds that it is the cell-wall of the alga that is mainly 

dissolved by the ferment and then used as food by the hyphae. 

No allowance has been made by Elenkin for the normal wasting common 

to all organic beings: the lichen fungus is continually being renewed, 

especially in the cortical structures, and the alga must also be subject to 

claims, nevertheless, that his observations have proved that the 

change. He 1 

one symbiont is always preying on the other, either as a parasite or as a 

saprophyte. He has likened the conception of symbiosis to that of a balance 

between two organisms, "a moveable equilibrium of the symbionts." If, he 

says, we could conceive a state where the conditions of life would be equally 

favourable for both partners there would be true mutualism, but in practice 

one only is favoured and gains the upper hand, using its advantage to prey 

on the other. Unless the balance is redressed, the complete destruction of 

the weaker is certain, and is followed in time by the death of the stronger. 

The fungus being the dominant partner, the balance, he considers, is tipped 

in its favour. 

Elenkin's conclusions are not borne out by the long continued and healthy 

life of the lichen. There is no record of either symbiont having succumbed 

to the other, and the alga, when set free, is unchanged and able to resume its 

normal development. Without the alga the fungus cannot form the ascigerous 

fruit. Is that because as a parasite within the lichen it has degenerated past 

recovery, or has it become so adapted to symbiosis that in saprophytic conditions 

it fails to develop ? 

Another Russian lichenologist, U. N. Danilov 2 

, records results which 

would seem to support the theory of parasitism. He found that from the 

clasping hyphae minute haustoria were produced, which penetrate the algal 

cell-wall, and branch when within the outer membrane, thus forming a 

delicate network over the plasma; secondary haustoria arising from this 

network protrude into the interior and rob the cell-contents. He observed 

gonidia filled with well-developed hyphae and these, after having exhausted 

one cell, travel onwards to others. Some gonidia under the influence of the 

fungus had become deformed and were finally killed. As a proof of this 

latter statement he adduces the presence in the thallus of some gonidia 

containing shrivelled protoplasm, of others entirely empty. He considers, as 

further evidence in favour of parasitism, the finding of empty membranes as 

1 Elenkin I9o6 2 . 

5G01.1 

2 Danilov 1910.

38 


well as of colourless gonidia filled with the hyphal network. This description 

hardly tallies with the usual healthy appearance of the gonidial zone in the 

normal thallus, and it has been suggested that where the fungus filled the 

algal cell, it was as a saprophyte preying on dead material. 

The gradual perishing of algal cells in time by natural decay and their 

subsequent absorption by the fungus is undisputed. It is open to question 

whether the varying results recorded by these workers have any further 

significance. 

These observations of Elenkin and Danilov have been proved to be 

erroneous by Paulson and Somerville Hastings 1 . They examined the thalli 

of several lichens (Xanthoria parietina, Cladonia sp., etc.) collected in early 

spring when vegetative growth in these plants was found to be at its highest 

activity. They found an abundant increase of gonidia within the thallus, 

which they regarded as sporulation of the algae, and the most careful methods 

of staining failed to reveal any case of penetration of the gonidia by the 

hyphae. 

Nienburg 2 has published some recent observations on the association of 

the symbionts. In the wide cortex of a Pertusaria he found not only the 

densely compact hyphae, but also isolated gonidia. In front of these latter 

there was a small hollow cavity and, behind, parallel hyphae rich in contents. 

These gonidia had originated from the normal gonidial zone. They were 

moved upward by special hyphae called by Nienburg "push-hyphae." After 

their transportation, the algae at once divide and the products of division 

pass to a resting stage and become the centre of a new thalline growth. A 

somewhat similar process was noted towards the apex of Evernia furfur acea. 

Radial hyphae pushed up the cortex, leaving a hollow space over the gonidial 

zone. Into the space isolated algae were thrust by "push-hyphae." In this 

lichen he also observed the penetration of the algal cell by haustoria of the 

fungus. He considers that the alga reaps advantage but also suffers harm, 

and he proposes the term helotism to express the relationship. 

An instructive case of the true parasitism of a fungus on an alga has been 

described by Zukal 3 in the case of Endomyces scytonemata which he calls 

a "half-lichen." The mature fungus formed small swellings on the filaments 

of the Scytonema and, when examined, the hyphae were seen to have attacked 

the alga, penetrating the outer gelatinous sheath and then using up the 

contents of the green cells. It is only after the alga has been destroyed and 

absorbed, that asci are formed by the fungus. Zukal contrasts the development 

of this fungus with the symbiotic growth of the two constituents in 

EpJiebe where both grow together for an indefinite time. 

Mere associated growth however even between a fungus and an alga 

does not constitute a lichen. An instance of such growth is described by 

1 Paulson and Hastings 1920. 

2 

Nienburg 1917. 

3 Zukaj l89I>

Sutherland ] 


in an account of marine microfungi. One of these, a species of 

Mycosphaerella, was found on Pelvetia canaliculata, and Sutherland claims 

that as no apparent injury was done to the alga, it was a case of 

symbiosis and that there was formed a new type of lichen. The mycelium, 

always intercellular, pervaded the whole host-plant, and the fungal fruits 

were invariably formed on the algal receptacles close to the oogonia. Their 

position there is, of course, due to the greater food supply at that region. 

Both fungus and alga fruited freely. A closer analogy could have been found 

by the writer in the smut fungus which grows 

with the host-cereal until 

fruiting time; or with the mycorrhiza of Calluna which also pervades every 

part of the host-plant without causing any injury. In the true lichen, the 

alga, though constituting an important part of the vegetative body, takes no 

part in reproduction, except by division and increase of the vegetative cells 

within the thallus. The fruiting bodies are always of a modified fungal 

nature. 

2. PHYSIOLOGY OF THE SYMBIONTS 

The occurrence of isolated cases of parasitisVn the fungus preying on 

the alga in any case leaves the general problem unsolved. The whole 

question turns on the physiological activity and requirements of the two 

component elements of the thallus. From what sources do they each 

procure the materials essential to them as living organisms? It is chiefly 

a question of nutrition. 

A. NUTRITION OF ALGAE 

a. CHARACTER OF ALGAL CELLS. Gonidia are chlorophyll-containing 

bodies and assimilate carbon-dioxide from the atmosphere by photo- 

synthesis as do the chlorophyll cells of other plants. They also require 

water and mineral salts which, in a free condition, they absorb from their 

immediate surroundings, but which, in the lichen thallus, they must obtain 

from the fungal hyphae. If the nutriment supplied to them in their inclosed 

position be greater or even equal to what the cells could procure as freeliving 

algae, then they undoubtedly gain rather than lose by their association 

with the fungus, and are not to be considered merely as victims of 

parasitism. 

b. SUPPLY OF NITROGEN. Important contributions on the subject of 

algal nutrition have been made by Beyerinck 2 and Artari 3 . The 

former 

conducted a series of culture experiments with green algae, including the 

gonidia of Physcia (Xanthoria) parietina. He successfully isolated the 

lichen gonidia and, at first, attempted to grow them on gelatine with an 

infusion of the Elm bark from which he had taken the lichen. Growth was 

1 Sutherland 1915. 

2 Beyerinck 1890. 

3 Artari 1902.

40 


very slow and very feeble until he added to the culture- medium a solution 

of malt-extract which contains peptones and sugar. Very soon he obtained 

an active development of the gonidia, and they multiplied rapidly by 

division 1 as in the lichen thallus. This proved to him conclusively the great 

advantage to the algae of an abundant supply of nitrogen. 

Artari in his work has demonstrated that there are two different physiological 

races of green algae: (i) those that absorb peptones which he 

designates peptone-algae 

and (2) those that do not so absorb peptones. 

He tested the cells of Cystococcus humicola taken from the thallus of Physcia 

parietina, and found that they belonged to the peptone group and were 

therefore dependent on a sufficiency of nitrogenous material to attain their 

normal vigorous growth. 

It was also discovered by Artari that the one 

race can be made by cultivation to pass over to the other: that ordinary 

algae can be educated to live on peptones, and peptone-algae to do without. 

We learn further from Beyerinck's researches that Ascomycetes, the 

group of fungi from which the hyphae of most lichens are derived, are 

what he terms ammonia^sugar fungi; that is to say, the hyphae can 

abstract nitrogen from ammonia salts and, with the addition of sugar, can 

form peptones. The lichen peptone-algae are thus evidently, by their 

contact with such fungi, in a favourable position for securing the nitro- 

genous food supply most suited to their requirements. In their deep-seated 

layers, they are to a large extent deprived of light, but it has been proved 

by Artari 2 in a series of culture experiments extending over a long period, 

that the gonidia of Xanthoria parietina remain green in the dark under 

very varied conditions of nutriment, though the colour is distinctly fainter. 

Recently Treboux 3 has revised the work done by Artari and Beyerinck 

in reference to Cystococcus humicola. He denies that two physiological races 

are represented in this alga, the lichen gonidia, in regard to the nitrogen 

that they absorb, behaving exactly as do the free-living forms of the species. 

He finds that the gonidium is not a peptone-carbohydrate organism in the 

sense that it requires nitrogen in the form of peptones, inorganic ammonia 

salts being a more acceptable food supply. Treboux concludes that his 

results favour the view that the gonidia are in an unfavourable situation for 

receiving the kind of nitrogenous compound most advantageous to them, 

that .they are therefore in a sense "victims" of parasitism, though he 

qualifies the condition as being a lichen-parasitism or helotism. This view 

does not accord with Chodat's 4 results: in his cultures of gonidia he 

observed that with glycocoll or peptone, which are nearly equivalent, they 

developed four times better than with potassium nitrate as their nitrogenous 

food, and he concluded that they assimilated nitrogen better from bodies 

allied to peptides. 

1 See p. 56. 

2 Artari 1902. 

3 Treboux 1912. 

4 Chodat 1913.

LICHEN. GONIDIA 41 

c. EFFECT OF SYMBIOSIS ON THE ALGA. Treboux's observations how- 

ever convinced him that the alga leads but a meagre existence within the 

thallus. Cell-division the expression of active vitality was, he held, of rare 

occurrence in the slowly growing lichen-plant, and zoospore formation in 

entire abeyance. He contrasts this sluggish increase 1 with the rapid multi- 

plication of the free-living algal cells which cover whole tree-trunks with 

their descendants in a comparatively short time. These latter cells, he 

finds, are indeed rather smaller, being generally the products of recent 

division, but mixed with them are numbers of larger resting cells, com- 

parable in size with the lichen gonidia. He states further, that the gonidia 

are less brightly green and, as he judges, less healthy, though in soredial 

formation or in the open they at once regain both colour and power of 

division. Treboux had entirely failed to observe the sporulation which is so 

abundant at certain seasons. 

Their quick recovery seems also a strong argument in favour of the 

absolutely normal condition of metabolism within the gonidial cell; and 

the paler appearance of the chlorophyll is doubtless associated with the 

acquisition of carbohydrates from other' sources than by photosynthesis. 

There is a wide difference between any degree of unfavourable life-conditions 

and parasitism however slight, even though the balance of gain is on the 

side of the fungus. It is not too fanciful to conclude that the demand for 

nitrogen on the part of the alga has influenced its peculiar association with 

the fungus. In the thallus of hypophloeodal lichens it has been proved 

indeed that the alga Trentepohlia with apical growth is an active agent in 

the symbiotic union. Cystococctis and other green algal cells are stationary, 

but they are doubtless equally ready for as many of them are equally 

benefited by the association. Keeble 2 has pointed out in the case of 

Convoluta roscoffensis that nitrogen-hunger induces the green algae to 

combine forces with an animal organism, though the benefit to them is only 

temporary and though they are finally sacrificed. The lichen gonidia, on 

the contrary, persist for a long time, probably far beyond their normal 

period of existence as free algae. 

Examples of algal association with other plants might be cited here: of 

Nostoc in the roots of Cycas and in the cells of Anthoceros, and of Anabczna 

in the leaf-cells of Azolla, but in these instances it is generally held that 

the alga secures only shelter. It was by comparing the lichen-association 

with the harmless invasion of Gunnera cells by Nostoc that Reinke 3 arrived 

at his conception of "consortism." 

d. SUPPLY OF CARBON. Carbon, the essential constituent of all organic 

life, is partly drawn from the carbon-dioxide of the air, and assimilated by 

1 See Paulson and Hastings 1920. 

2 Keeble 1910. 

3 Reinke 1872.

42 


the green cells; it is also partly contributed by the fungus as a product of 

its metabolism. A proof of this is afforded by Dufrenoy 1 : he found a 

Parmelia growing closely round pine needles and even sending suckers into 

the stomata. He covered the lichen with a black cloth and after seven weeks 

found that the gonidia had remained very green. That growth had not 

been checked was evidenced by an unusual development of soredia and 

of spermogonia. Dufrenoy describes the condition as a parasitism of the 

algae on the fungus which in turn was drawing nourishment from the 

pine needles. 

Artari 2 has proved that lichen gonidia can obtain carbohydrates from 

the substratum as well as by photosynthesis. He cultivated the gonidia of 

Xanthoria parietina and Placodium murorum on media which contained 

organic substances as well as mineral salts, while depriving them of atmo- 

spheric carbon-dioxide and in some cases of light also. The gonidia not 

only grew well but, even in the dark, they remained normally green, a 

3 

phenomenon coinciding with Etard and Bouilhac's experience in growing 

Nostoc in the dark: with suitable culture media the alga retained its colour. 

Nostoc also grows in the dark in the rhizome of Gunnera. Radais' 4 

experi- 

ments with Chlorella vulgaris confirmed these results. On certain organic 

media growth and cell-division were as rapid in the dark as in the light, 

and chlorophyll was formed. The colour was at first yellowish and the full 

green arrived slowly, especially on sugar media, but in ten days it was 

uniform and normal. 

When making further experiments with the alga, Siichococcus badllaris, 

Artari 5 found that it also grew well on an organic medium and that grape 

sugar was the most valuable carbonaceous food supply. Chodat 6 also found 

that sugar or glucose was a desirable ingredient of culture media. 

Treboux 7 

, in his work on organic acids, has also proved by experimental 

cultures with a large series of algae, including the gonidia of Peltigera, that 

these green plants in the absence of light and in pure cultures would grow 

and form carbohydrates if the culture medium contained a small percentage 

of organic acids. The acids he employed were combined with potassium 

and were thus rendered neutral or slightly alkaline; acetate of potash 

proved to be the most advantageous compound of Amino-acids and 

any that was tested. 

ammonia salts were added to provide the necessary 

nitrogen. Oxalic acid and other organic acids of varying composition are 

peculiarly abundant in lichen tissues and may be a source of carbon supply. 

Marshall Ward 8 has found calcium carbonate crystals in the lower air- 

containing tissues of Strigula complanata. 

Treboux finally concluded from his researches that just as fungi can 

1 

2 

i Dufrenoy 19 8. Artari 1899. Etard and Bouilhac 1898. 

6 

Artari 1901. Chodat ? 

1913. Treboux 1905. 

4 Radais 1900. 

8 Marshall Ward 1884.


extract carbohydrates from many sources, so algae can secure their carbon 

supply in a variety of ways. He affirms that the metabolic activity of the 

alga in these cultural conditions is entirely normal, and the various cellcontents 

are formed as in the light. Whether, in this case, starch is formed 

directly from the acids or through a series of combinations has not been 

determined. Uhlir 1 

, with electric lighting, made successful cultures of 

Nostoc isolated from Collemaceae on silicic acid, proving thereby that these 

gonidia do not require a rich nutriment. A certain definite humidity was 

however essential, and bacteria were never eliminated as they are associated 

with the gelatinous membranes of Nostocaceae. 

e. NUTRITION WITHIN THE SYMBIOTIC PLANT. Culture experiments 

bearing more directly on the nutrition of lichens as a whole were carried 

out by F. Tobler 2 . He proved that the gonidia had undoubtedly drawn on 

the calcium oxalate secreted by the hyphae for their supply of carbon. In 

a culture medium of poplar-bark gelatine he grew hyphae of Xantkoria 

parietina, and noted an abundant deposit of oxalate crystals on their cell- 

walls. A piece of the lichen thallus including both symbionts and grown on 

a similar medium formed no crystals, and microscopic examination showed 

that crystals were likewise absent from the hyphae of the thallus that had 

grown normally on the tree, the inference being that the gonidia used them up 

as quickly as they were deposited. It must be remembered in this connection, 

however, that Zopf 3 has stated that where lichen acids are freely formed 

as, for instance, in Xanthoria parietina, there is always less formation and 

deposit of calcium oxalate crystals, which may partly account for their 

absence in the normal thallus so rich in parietin. 

Tobler next introduced lichen gonidia into a culture medium in which 

the isolated hyphal constituent of a thallus had been previously cultivated, 

and placed the culture in the dark. In these circumstances he found that 

the gonidia were able to thrive but formed no colour: they were obtaining 

their carbohydrates, he decided, not from photosynthesis, but from the 

excretory products such as calcium oxalate that had been deposited in the 

culture medium by the lichen hyphae. We may conclude with more or less 

certainty that the loss of carbohydrates, due to the partial deprivation of 

light and air suffered by the alga owing to its position in the lichen thallus, 

is more than compensated by a physiological symbiosis with the fungus 4 . 

It has indeed been proved that in the absence of free carbon-dioxide, algae 

may utilize the half-bound CO2 of carbonates, chiefly those of calcium and 

dissolved in water. 

magnesium, 

/ AFFINITIES OF LICHEN GONIDIA. Chodat 5 

has, in recent years, 

made cultures of lichen gonidia with a view to discovering their relation to 

1 Uhlir 1915. 

2 Tobler 1911. 

3 Zopf 1907. 

* Chambers 1912. 

5 Chodat 1913

44 


free-living algae and to testing at the same time their source of carbon 

supply. He has come to the conclusion that lichen gonidia are probably in 

no instance the normal Protococcus viridis: they differ from that alga in the 

possession of a pyrenoid and in their reproduction by zoospores when free. 

Careful cultures were made of different Cladonia gonidia which were 

morphologically indistinguishable, and which varied in size from 10 to 16/4 

in diameter, though smaller ones were always present. He recognized them 

to be species of Cystococcus: they have a pyrenoid 1 in the centre and a 

disc-like chromatophore more or less starred at the edge. These gonidia 

grew well on agar, still better on agar-glucose, but best of all with an 

addition of peptone to the culture. There was invariably at first a slight 

difference in form and colour in the mass between the gonidia of one 

species and those of another, but as growth continued they became alike. 

In testing for carbon supply, he found that gonidia grew slowly without 

sugar (glucose), and that, as sources of carbon, organic acids could not 

entirely replace glucose though, in the dark, the gonidia used them to some 

extent; the colony supplied with potassium nitrate, and grown in the dark, 

had reached a diameter of only 2 mm. in three months. With glucose, it 

measured 5 mm. in three weeks, while in three months it formed large 

culture patches. 

A further experiment was made to test their absorption of peptones by 

artificial cultures carried out both in the light and the dark. The gonidia 

grew poorly in all combinations of organic nitrogen compounds. When 

combined with glucose, growth was at once more vigorous though only half 

as much in the dark as in the light, the difference in this respect being 

especially noticeable in the gonidia from Cladonia pyxidata. He concludes 

that as gonidia in these cultures are saprophytic, so in the lichen thallus 

also they are probably more or less saprophytic, obtaining not only their 

nitrogen in organic form but also, when possible, their carbon material as 

glucose or galactose from the hyphal symbiont which in turn is saprophytic 

on humus, etc. 

B. NUTRITION OF FUNGI 

Fungi being without chlorophyll are always indebted to other organisms 

for their supply of carbohydrates. There has never therefore been any 

question as to the advantage accruing to the hyphal constituent in the 

composite thallus. The gonidia, as various workers have proved, have also 

a marked preference for organized nourishment, and, in addition, they obtain 

carbon by photosynthesis. Chodat 2 considers that probably they are thus 

able to assimilate carbon-dioxide in excess, a distinct advantage to the 

hyphae. In some instances the living gonidium 

is invaded and the contents 

1 See note Paulson and Hastings, p. 28. 2 Chodat 1913.


used up by the fungus and any dead gonidia are likewise utilized for food 

supply. It is also taken for granted that the fungus takes advantage of the 

presence of humus whether in the substratum or in aerial dust. In such 

slow growing organisms, there is not any large demand for nourishment on 

the part of the hyphae: for many lichens it seems to be mere subsistence 

with a minimum of growth from year to year. 

C. SYMBIOSIS OF OTHER PLANTS 

The conception of an advantageous symbiosis of fungi with other plants 

has become familiar to us in Orchids and in the mycorhizal formation on 

the roots of trees, shrubs, etc. Fungal hyphae are also frequent inhabitants 

of the rhizoids of hepatics though, according to Gargeaune 1 

, 

the benefit to 

the hepatic host-plant is doubtful. 

An association of fungus and green plant of great interest and bearing 

directly on the question of mutual advantage has been described by 

Servettaz 2 . In his study of mosses, he was able to confirm Bonnier's 3 

account of lichen hyphae growing over such plants as Vaticheria and 

the protonema of mosses, which is undoubtedly hurtful; but he also found 

an association of a moss with one of the lower fungi, Streptothrix or 

Oospora, which was distinctly advantageous. In separate 

cultivation the 

fungus developed compact masses and grew well in peptone agar broth. 

Cultures of the moss, Phascum cuspidatum, were also made from the 

spores on a glucose medium. The specimens in association with the fungus 

were fully grown in two months, while the control cultures, without any 

admixture of the fungus, had not developed beyond the protonema stage. 

Servettaz draws attention to the proved fact that, in certain instances, 

plants benefit when provided with substances similar to their own decay 

products, and he considers that the fungus, in addition to its normal gaseous 

products, has elaborated such substances, as acid products, from the glucose 

medium to the great advantage of the moss plant. 

A symbiotic association of Nostoc with another alga, described by 

Wettstein 4 

, is also of interest. The blue-green cells were lodged in the 

pyriform outgrowths of the siphoneous alga, Botrydium pyriforme Kiitz., 

which the author of the paper places in a new genus, Geosiphon. The 

sheltering Nostoc symbioticum fills all of the host left vacant by the plasma, 

and when the season of decay sets in, it forms resting spores which migrate 

into the rhizoids of the host, so that both plants regenerate together. 

Wettstein has compared this symbiotic association with that of lichens, 

and finds the analogy all the more striking in that the membrane of his new 

alga had become chitinous, which he thinks may be due to organic nutrition. 

1 

Gargeaune 1911. 

2 Servettaz 1913. 

3 See p. 65. 

4 Wettstein 1915.

46 


II. LICHEN HYPHAE 

A. ORIGIN OF HYPHAE 

Lichen hyphae form the ground tissue of the thallus apart 

from the 

gonidia or algal cells. They are septate branched filaments of single cell 

rows and are colourless or may be tinged by pigments or lichen acids to 

some shade of yellow, brown or black. They are of fungal nature, and are 

produced by the mature lichen spore. 

The germination of the spore was probably first observed by Meyer 1 

. 

His account of the actual process is somewhat vague, and he misinterpreted 

the subsequent development into thallus and fruit entirely for want of the 

necessary magnification; but that he did succeed in germinating the spores 

is unquestionable. He cultivated them on a smooth surface and they grew 

into a "dendritic formation" a true hypothallus. Many years later the 

development of hyphae from lichen spores was observed by Holle 2 who saw 

and figured the process unmistakably in Borrera (Physcici) ciliaris. 

A series of spore cultures was undertaken by Tulasne 3 with the twofold 

object of discovering the exact origin of hyphae and gonidia and of their 

relationship to each other. The results of his classical experiment with the 

spores of Verrucaria muralis as interpreted by him were accepted by the 

lichenologists of that time as conclusive evidence of the genetic origin of the 

gonidia within the thallus. 

The spores- of the lichen in large numbers had been sown by Tulasne 

in early spring on the smooth polished surface of a piece of limestone, and 

Fig. 14. Germinating spores of Verrucaria nmralis Ach. after two 

months' culture x ca. 500 (after Tulasne). 

were covered with a watch-glass to protect them from dust, etc. At 

irregular intervals they were moistened with water, and from time to time 

1 

* Meyer 1825. 

Ho,,e ^ ^^ ^.^ 

,

LICHEN HYPHAE . 47 

a few spores were abstracted from the culture and examined microscopically. 

Tulasne observed that the spore did not increase or change in volume in the 

process of germination, but that gradually the contents passed out into the 

growing hyphae, till finally a thin membrane only was left and still persisted 

after two months (Fig. 14). For a considerable time there was no septation ; 

at length cross-divisions were formed, at first close to the spore, and then 

later in the branches. The hyphae meanwhile increased in dimension, the 

cells becoming rounder and somewhat wider, though always more slender 

than the spore which had given rise to them. In time a felted tissue was 

formed with here and there certain cells, filled with green colouring matter, 

similar to the gonidia of the lichen and thus the early stages at least of a 

new thallus were observed. The green cells, we now know, must have gained 

entrance to the culture from the air, or they may have been introduced with 

the water. 

B. DEVELOPMENT OF LICHENOID HYPHAE 

Lichen hyphae are usually thick-walled, thus differing from those of fungi 

generally, in which the membranes, as a rule, remain comparatively thin. 

This character was adduced by the so-called "autonomous" school as a proof 

of the fundamental distinction between the hyphal elements of the two 

groups of plants. It can, however, easily be observed that, in the early 

stages of germination, the lichen hyphae, as they issue from the spore, are 

thin-walled and exactly comparable with those of fungi. Growth is apical, 

and septation and branching arise exactly as in fungi, and, in certain circum- 

stances, anastomosis takes place between converging filaments. But if algae 

are present in the -culture the peculiar lichen characteristics very soon 

appear. 

Bonnier 1 who , 

made a large series of synthetic cultures, distinguishes 

three types of growth in lichenoid hyphae (Fig. 15): 

1. Clasping filaments, repeatedly branched, which attach and surround 

the algae. 

2. Filaments with rather short swollen cells which ultimately form the 

hyphal tissues of cortex and medulla. 

3. Searching filaments which elongate towards the periphery and go to 

the encounter of new algae. 

In five days after germination of the spores, the clasping hyphae had 

laid hold of the algae which meanwhile had increased by division; the 

swollen cells had begun to branch out and ten days later a differentiation 

of tissue was already apparent. The searching filaments had increased in 

number and length, and anastomosis between them had taken place when 

1 Bonnier i88q 2 .

48 


no further algae were encountered. The cell-walls of the swollen hyphae 

and their branches had begun to thicken and to become united to form a kind 

1 

of cellular tissue or ." 

"paraplectenchyma 

At a later date, about a month 

Fig. 15. Synthetic culture of Physcia parietina spores and Protococcus 

viridis five days after germination, s, lichen-spore ; a, septate filaments 

; b, clasping filaments; c, searching filaments, x 500 (after 

Bonnier). 

after the sowing of the spores, there was a definite cellular cortex formed 

over the thallus. The hyphal cells are uninucleate, though in the medulla 

they may be i-2-nucleate. 

The hyphae in close contact with the gonidia remain thin- walled, and 

have been termed by Wainio 2 "meristematic." They furnish the growing 

elements of the lichen either apical or intercalary. In most genera the organs 

of fructification take rise from them, or in their immediate neighbourhood, 

and isidia and soredia also originate from these gonidial hyphae. 

As the filaments pass from the gonidial zone to other layers, the cell- 

walls become thicker with a consequent reduction of the cell-lumen, very 

noticeable in the pith, but carried to its furthest extent in the "decomposed" 

cortex where the cells in the degenerate tissue often become reduced to dis- 

connected streaks indicating the cell-lumen, and the outer cortical layer is 

merely a continuous mass of mucilage. 

All lichen -tissues arise from the branching and septation of the hyphae, 

the septa always forming at right angles to the long axis of the filaments. 

There is no instance of longitudinal cell-division except in the spores of 

certain genera (Collema, Urceolaria, Polyblastia, etc.). The branching of the 

hypha is dichotomous or lateral, and very irregular. Frequent septation and 

coherent growth result in the formation of plectenchyma. 

1 Term coined by Lindau (1899) to describe the pseudo-cellular tissue of lichens and fungi now 

referred to as "plectenchyma." 

2 Wainio 1897.

LICHEN HYPHAE 49 

C. CULTURE OF HYPHAE WITHOUT GONIDIA 

Artificial cultures had demonstrated the germination of lichen spores, 

with the formation of hyphae, and from synthetic cultures of fungus and 

alga complete lichen plants had been produced. To Moller 1 we owe the first 

cultures of a thalline body from the fungus alone, both from spermatia and 

from ascospores. The germination of the spermatia has a direct bearing 

on their function as spores or as sexual organs and is described in a 

later chapter. 

The ascospores of Lecanora sitbfusca were caught in a drop of water on 

a slide as they were ejaculated from the ascus, and, on the following day, a 

very fine germinating tube was seen to have pierced the exospore. The 

hypha became slightly thicker, and branching began on the third day. If 

in water alone the culture soon died off, but in a nutrient solution growth 

slowly continued. The hyphae branched out in all directions from the spore 

as a centre and formed an orbicular expansion which in fourteen days had 

reached a size of 'I mm. in diameter. After three weeks' growth it was large 

enough to be visible without a lens ; 

the mycelial threads were more crowded, 

and certain terminal hyphae had branched upwards in an aerial tuft, this 

development taking place from the centre outwards. Moller marked this 

stage as the transition from a mere protothallus to a thallus formation. In 

three months a diameter of i'5-2 mm. was reached; a transverse section 

gave a thickness of "86 mm. and from the under side loose hyphae branched 

downwards and attached the thallus, when it had been transferred to a solid 

substratum such as cork. Above these rhizoidal hyphae, a stratum of rather 

loose mycelium represented the medulla, and, surmounting that, a cortical 

layer in which the hyphae were very closely compacted. Delicate terminal 

branches rose into the air over the whole surface, very similar in character 

to hypothallic hyphae at the margin of the thallus. 

Lecanora subfusca has a rather small simple spore; it emitted germinating 

tubes from each end, and a septum across the middle of the spore appeared 

after germination had taken place. Another experiment was with a much 

in thickness. On 

larger muriform spore measuring 80^, in length and 20 //, 

germination about 20 tubes were formed, some of them rising into the air at 

once, the others encircling the spore, so that the thallus took form imme- 

diately; growth in this case also was centrifugal. In three months a diameter 

of 6 mm. was reached with a thickness of I to 2 mm. and showing a differen- 

tiation into medulla and cortex. The hyphae did not increase in width, but 

frequently globose or ovate swellings arose in or at the ends, a character which 

recurs in the natural growth of hyphae both of lichens and of Ascomycetes. 

These swellings depend on the nutrition. 

1 Moller 1887.

50 


Pertusaria communis possesses a very large simple spore, but it is multi- 

nucleate and germinates with about 100 tubes which reach their ultimate 

width of 3 to 4 /x before they emerge from the exospore. The hyphae 

encircle the spore, and an opaque thalline growth is quickly formed from 

which rise terminal hyphal branches. In ten weeks the differentiation into 

medulla and cortex was reached, and in five months the hyphal thallus 

measured 4 mm. in diameter and i to 2 mm. in thickness. 

Moller instituted a comparison between the thalli he obtained from the 

spores and those from the spermatia of another crustaceous lichen, Buellia 

punctiformis (B. myriocarpa). After germination had taken place the hyphae 

from the spermatia grew at first more quickly than those from the ascospores, 

but as soon as thallus formation began the latter caught up and, in eight 

weeks, both thalli were of equal size. 

Another comparative culture with the spermatia and ascospores of 

Opegrapha subsiderella gave similar results: the spores of that species are 

elongate-fusiform and 6- to 8-septate; germination took place from the end 

cells in two to three days after sowing. The germinating hyphae corre- 

sponded exactly with those from the spermatia and growth was equally slow 

in both. The middle cells of the spores may also produce germinating tubes, 

but never more than about five were observed from any one spore. A 

browning of the cortical layer was especially apparent in the hyphal culture 

from another lichen, Graphis scripta: a clear brown colour gradually changing 

to black appeared about the same period in all the cultures. 

The hyphae from the spores of Arthonia developed quickest of all: the 

hyphae were very slender, btt in three to four months the growth had reached 

a diameter of 8 mm. In this plant there was the usual outgrowth of delicate 

hyphae from the surface; no definite cortical layer appeared, but only a very 

narrow line of more closely interwoven somewhat darker hyphae. Frequently, 

from the surface of the original thallus, excrescences arose which were the 

beginnings of further thalli. 

Tobler 1 

experimenting with Xanthoria parietina gained very similar 

results. The spores were grown in malt extract for ten days, then transferred 

to gelatine. In three to five weeks there was formed an orbicular mycelial 

felt about 3 mm. in diameter and 2 mm. thick. The mycelium was frequently 

brownish even in healthy cultures, but the aerial hyphae which, at first, rose 

above the surface were always colourless. After these latter disappeared a 

distinct brownish tinge of the thallus was visible. In seven months it had 

increased in size to 15 mm. in length, 7 mm. in width and 3 mm. thick with 

a differentiation into three layers: a lower rather dense tissue representing 

the pith, above that a layer of loose hyphae where the gonidial zone would 

1 Tobler 1909.

LICHEN HYPHAE 51 

normally find place, and above that a second compact tissue, or outer cortex, 

from which arose the aerial hyphae. The culture could not be prolonged 

more than eight months. 

D. CONTINUITY OF PROTOPLASM IN HYPHAL CELLS 

Wahrlich 1 demonstrated that continuity of protoplasm was as constant 

between the cells of fungi as it has been proved to be between the cells of 

the higher plants. His researches included the hyphae of the lichens, Cla- 

donia fimbriata and Physcia (Xanthoria) parietina. 

Baur 2 and Darbishire 3 found independently that an open connection 

existed between the cells of the carpogonial structures in the lichens they 

examined. The subject as regards the thalline hyphae was again taken up 

by Kienitz-Gerloff4 who obtained his best results in the hypothecial tissue 

of Peltigera canina and P. polydactyla. Most of the cross septa showed one 

central protoplasmic strand traversing the wall from cell to cell, but in some 

instances there were as many as four to six pits in the walls. The thickening 

of the cell-walls is uneven and projects variously into, the cavity of the cell. 

Meyer's 5 work was equally conclusive: all the cells of an individual hypha, 

he found, are in protoplasmic connection ; and in plectenchymatous tissue 

the side walls are frequently perforated. Cell-fusions due to anastomosis are 

frequent in lichen hyphae, and the wall at or near the point of fusion is also 

traversed by a thread of protoplasm, though such connections are regarded 

as adventitious. Fusions with plasma connections are numerous in the 

matted hairs on the upper surface of Peltigera canina and they also occur 

between the hyphae forming the rhizoids of that lichen. The work of Salter 6 

may also be noted. He claimed that his researches tended to show complete 

anatomical union between all the tissues of the lichen plant, not only between 

the hyphae of the various tissues but also between hyphae and gonidia. 

III. LICHEN ALGAE 

A. TYPES OF ALGAE 

The algal constituents of the lichen thallus belong to the two classes, 

Myxophyceae, generally termed blue-green algae, and Chlorophyceae which 

are coloured bright-green or yellow-green. Most of them are land forms, 

and, in a free condition, they inhabit moist or shady situations, tree-trunks, 

walls, etc. They multiply by division or by sporulation within the thallus; 

zoospores are never formed except in open cultivation. The determination 

of the genera and species to which the lichen algae severally belong is often 

uncertain, but their distribution within the lichen kingdom is as follows: 

1 Wahrlich 1893. 

4 Kienitz-Gerloff 1902. 

2 Baur 1898. 

5 

Meyer 1902. 

3 Darbishire 1899. 

6 Salter 1902. 

42


a. MYXOPHYCEAE ASSOCIATED WITH PHYCOLICHENS. The blue-green 

algae are characterized by the colour of their pigments which persists 

in the gonidial condition giving various tints to the component lichens, and 

by the gelatinous sheath in which most of them are enclosed. This sheath, 

both in the lichen gonidia 1 and in free-living forms, imbibes and retains 

moisture to a remarkable extent and the thallus containing blue-green algae 

profits by its power of storing moisture. Myxophyceae form the gonidia 

of the gelatinous lichens as well as of some other non-gelatinous genera. 

Several families are represented 2 : 

Fam. CHROOCOCCACEAE. This family includes unicellular algae with 

thick gelatinous sheaths. They increase normally by division, and colonies 

arise by the cohesion of the cells. Several genera form gonidia: 

1. CHROOCOCCUS Naeg. Solitary or forming small colonies of 2-4-8 

cells (Fig. 1 6) generally surrounded by firm gelatinous colourless sheaths in 

definite layers (lamellate). Chroococcus is considered by some lichenologists 

to form the gonidium of Cora, a genus of Hymenolichens. 

2. MlCROCYSTis Kiitz. Globose or subglobose cells forming large 

colonies surrounded by a common gelatinous layer (gonidia of Coris- 

cium). 

3. GLOEOCAPSA Kiitz. (including Xanthocapsd). Globose cells with a 

Fig. 16. Examples of Chroococcus. A, Ch. gigantens 

West ; B, Ch. turgidus Naeg. ; C and D, Ch. schizodermaticus 

West x 450 (after West). 

wm 

WB 

Fig. 17. Gloeocapsa magma 

Kiitz. x 450 (after West). 

lamellate gelatinous wall, forming colonies enclosed in a common sheath 

(Fig. 17); the inner integument is often coloured red or orange. These 

1 

Nylander (1866) gave the term "gonimia" to the blue-green algae of the Phycolichens, retaining 

the term " gonidia " for the bright-green algae of the Archilichens : the distinction is not now main- 

tained. 

2 For further details see also the chapter on Classification.

LICHEN ALGAE 53 

two genera form the gonidia in the family Pyrenopsidaceae. Gloeocapsa 

polydermatica Kiitz. has been identified as a lichen gonidium. 

Fam. NOSTOCACEAE. Filamentous algae unbranched and without base 

or apex. 

NOSTOC Vauch. Composed of flexuous trichomes, with 

intercalary 

Dense gelatinous colonies of definite 

heterocysts (colourless'cells) (Fig. 1 8). 

Fig. 18. Examples of Nostoc. N. Linckia Born. A, nat. size ; B, small portion x 340 ; 

C, N. coerulescens Lyngbye, nat. size (after West). 

Fig. 19. Example of Scytnnema alga. 5. mirabile Thur. C, apex of a branch ; D, organ 

of attachment at base of filament." x 440 (after West). 

form are built up by cohesion. In some lichens the trichomes retain their 

chain-like appearance, in others they are more or less broken up and massed 

together, with disappearance of the gelatinous sheath (as in Peltigera); 

colour mostly dark blue-green. 

Nostoc occurs in a few or all of the genera of Pyrenidiaceae, Collemaceae, 

Pannariaceae, Peltigeraceae and Stictaceae, and N. sphaericum Vauch

54 


(N. lichenoides Kutz.) has been determined as the lichen gonidium. When 

the chains are broken up it has been wrongly classified as another alga, 

Poly coccus punctiformis. 

Fam. SCYTONEMACEAE. Trichomes of single-cell rows, differentiated into 

base and apex. Pseudo-branching arises at right angles to the main filament. 

SCYTONEMA Ag. Pseudo-branches piercing the sheath and passing out 

as twin filaments (Fig. 19); colour, golden-brown. This alga occurs in 

genera of Pyrenidiaceae, Ephebaceae, Pannariaceae, Heppiaceae, in Petractis 

a genus of Gyalectaceae, and in Dictyonema one of the Hymenolichens. 

Fam. STIGONEMACEAE. Trichomes of several-cell rows with base and 

apex ; colour, golden-brown. 

STIGONEMA Ag. Stouter than Scytonema, with transverse and vertical 

division of the cells, and generally copious branching (Fig. 20). This alga 

occurs only in a few genera of Ephebaceae. S.panniforme Kirchn. (Siro- 

siphon pulvinatus Breb.) has been determined as forming the gonidium. 

Fam. RIVULARIACEAE. Trichomes with a heterocyst at the base and 

tapering upwards, enclosed in mucilage (Fig. 21). 

Fig. 20. Stigonema sp. x 200 (after 

Comere). 

-**-* 1 

Fig. 21. Examples of Rivularia ; A, B, ,R.Biasokttiana 

Menegh. ; D and E, R. minutula 

Born, and Fl. A and D nat. size; B, C and E 

x 48o (after West).


RlVULARiA Thuret. In tufts fixed at the base and forming roundish 

gelatinous colonies; colour, blue-green. The gonidium of Lichinaceae has 

been identified as R. nitida Ag. 

Algae belonging to one or other of these genera of Myxophyceae also 

combine with the hyphae of Archilichens to form cephalodia 1 and Krem- 

pelhuber 2 has recorded and figured a blue-green alga, probably Gloeocapsa, 

in Baeomyces paeminosus from the South Sea Islands. They also form the 

gonidia in a few species and genera 

Peltigeraceae. 

of such families as Stictaceae and 

b. CHLOROPHYCEAE ASSOCIATED WITH ARCHILICHENS. The lichens of 

this group are by far the most numerous both in genera and species, though 

fewer algal families are represented. 

Fam. PROTOCOCCACEAE. Consisting of globular single cells, aggregated 

in loose colonies, dividing variously. 

i. PROTOCOCCUS VIRIDIS Ag. (Pleurococcus vulgaris Menegh., Cystococ- 

cushumicola Naeg.). Cells dividing 

into 2, 4 or 8 daughter-cells and 

not separating readily; in exces- 

sive moisture forming short fila- 

ments. The cells contain parietal 

chloroplasts, and, according to 

Chodat 3 

, are without a pyrenoid 

(Fig. 22). This alga, and allied 

species, forms the familiar green 

coating of tree-trunks, walls etc., 

and, in lichenological literature, 

are quoted as the gonidia of most 

of the crustaceous foliose and fruticose 

lichens. Chodat 3 who has 

, 

Fig. 22. Pleurococcus vulgaris Menegh. (Protococcus 

viridis Ag. ). chl. chloroplast ; p. protoderma 

stage; /


of species and he designates the algae, according to the lichen in which 

they occur, as Cystococcus Cladoniae pyxidatae, C. Cladoniae Jimbriatae, etc. 

Meanwhile Paulson and Somerville Hastings 1 

by their careful research 

on the growing thallus have thrown considerable light on the identity of the 

Protococcaceous lichen gonidium. They selected such well-known lichens 

as Xanthoria parietina, Cladonia spp. and others, which they collected 

during the spring months, February to April, the period 

Fig. 23. Cystococcus Cladoniae 

pyxidatae Chod. from culture 

x 800 (after Chodat). 

of most active 

growth. Many of the gonidia, they found, were in a stage of reproduction, 

that showed a simultaneous rounding off of the 

gonidium contents into globose bodies varying in 

number up to 32. Chodat had figured this method 

of "sporulation" in his cultures of the lichen gonidium 

both in Chlorella Beij. and in Cystococcus Chod. 

(Fig. 23). It has now been abundantly proved that 

this form of increase is of frequent occurrence in the 

thallus itself. Chlorella has been suggested as .prob- 

ably the alga forming these gonidia and recently 

West has signified his acquiescence in this view 2 . 

2. CHLORELLA Beij. Occurring frequently on damp ground, 

'ig. 23 A. A, C, Chlorella vulgaris 

Beyer. B and C, stages in division 

x about 800 (after ; Chodat) E, 

Chi. faginea Wille x 520 (after 

Gerneck); F I Chi. miniata ; F, 

vegetable cell G ; I, formation 

and escape of gonidia x 1000 

(after Chodat). 

bark of 

trees, etc., dividing into numerous daughter- 

cells, probably reduced zoogonidia (Fig. 23). 

Chodat distinguishes between Cystococcus 

and Chlorella in that Cystococcus may form 

zoospores (though rarely), Chlorella only 

aplanospores. He found three gonidial species, 

Chlorella lichina in Cladonia rangiferina, Ch. 

viscosa and Ch. Cladoniae in other Cladonia 

spp. 

3. COCCOBOTRYS Chod. The cells of this 

new algal genus are smaller than those of 

Cystococcus oxProtococcus and have no pyrenoid. 

They were isolated by Chodat from the thallus 

of Verrucaria nigrescens (Fig. 24), and, as 

they have thick membranes, they adhere in 

a continuous layer or thallus. Chodat also 

claims to have isolated a species of Cocco- 

botrys from Dermatocarpon miniatum, a foliose 

Pyrenolichen. 

4. COCCOMYXA Schmidle. Cells ellipsoid, also without a pyrenoid. 

Two species were obtained by Chodat from the thallus of Solorinae and 

are recorded as Coccomyxa Solorinae croceae and C. Solorinae saccatae. 

1 Paulson and Hastings 1920. 

2 Paulson in litt.


Coccomyxa subellipsoidea is given 1 as the gonidium of the primitive 

lichen Botrydina vulgaris (Fig. 25). The cells are surrounded by a common 

gelatinous sheath. 

Fig. 24. Coccobotrys Verrucariae Chod. 

from culture x 800 (after Chodat). 

Fig. 25. Coccomyxa subellipsoidea Acton. 

Actively dividing cells, the dark portions 

indicating the chloroplasts x 1000 (after 

Acton). 

5. DiPLOSPHAERA Bial. 2 D. Chodati was taken from the thallus of 

Lecanora tartarea and successfully cultivated. It resembles Protococcus^ but 

has smaller cells and grows more rapidly ; it is evidently closely allied to 

that genus, if not merely a form of it. 

6. IJROCOCCUS Kiitz. Cells more or less globose, rather large, and 

coloured with a red-brown pigment, with the cell-wall thick and lamellate, 

forming elongate strands of cells (Fig. 26). Recorded by Hue 3 in the 

cephalodium of Lepolichen coccopkora, a Chilian lichen. 

Fam. TETRASPORACEAE. Cells in groups of 2 or 4 surrounded by a 

gelatinous sheath. 

i . PALMELLA Lyngb. Cells globose, oblong or ellipsoid, grouped without 

order in a formless mucilage (Fig. 27). Among lichens associated with 

Palmella are the Epigloeaceae and Chrysothricaceae. 

Fig. 26. Urococcus sp. Group of cells 

much magnified (after Hassall). 

Fig. 27. Palmella sp. x 400 (after Comere). 

2. GLOEOCYSTIS Naeg. Cells oblong or globose with a lamellate 

sheath forming small colonies ; colour, red-brown 

(Fig. 28). 

found by 

This alga along with Urococcus was 

Hue in the cephalodia of Lepolichen 

coccophora, but whereas Gloeocystis frequently occu- 

pies the cephalodium alone, Urococcus is always 

accompanied by Scytonema, the normal gonidium 

of the cephalodium. 

1 Acton 1909. 

Fig. 28. Gloeocystis sp. x 400 

(after Comere). 

- Bialosuknia 1909. Hue 1905.


iff. 29- A, Trentepohlia umbrina Born ; 

K, /. aurea Mart, x 300 (after Kiitz.). 

Fig. 30. Example of Cladophora. Cl. glomerata Klitz 

A.nat. s,ze; B, x 85 (after West).


Fam. TRENTEPOHLIACEAE. Filamentous and branched, the filaments 

short and creeping or long and forming tufts and felts or cushions; colour, 

brownish-yellow or reddish-orange. 

TRENTEPOHLIA Born. Branching alternate; 

cells filled with red or 

orange oil ; no pyrenoids (Fig. 29). A large number of lichens are associated 

with this genus : Pyrenulaceae, Arthoniaceae, Graphidaceae, Roccellaceae, 

Thelotremaceae, Gyalectaceae and Coenogoniaceae, etc., in whole or in part. 

Two species have been determined, T. umbrina Born., the gonidium of the 

Graphidaceae, and T. aurea which is associated with the only European 

Coenogonium, C. ebeneum (Fig. 3). Deckenbach 1 claimed that he had proved 

by cultures that T. umbrina was a growth stage of T. aurea. 

Fam. CLADOPHORACEAE. Filamentous, variously and copiously branched, 

the cells rather large and multinucleate. 

CLADOPHORA Klitz. Filaments branching, of one-cell rows, attached 

at the base ; colour, bright or dark green ; mostly aquatic and marine 

(Fig. 30). Only one lichen, Racodium rupestre, a member of the Coeno- 

goniaceae, is associated with Cladophora. It is a British lichen, and is always 

sterile. 

Fam. MYCOIDEACEAE. Epiphytic algae consisting of thin discs which 

are composed of radiating filaments. 

1. MYCOIDEA Cunningh. (Cephaleuros Kunze). In Mycoidea parasitica 

the filaments of the disc are partly 

erect and partly decumbent, reddish 

to green (Fig. 31). It forms the gonidium 

of the parasitic lichen, Strigula 

complanata, which was studied by 

Marshall Ward in Ceylon 2 . Zahl- 

bruckner gives Phyllactidium as an 

alternative gonidium of Strigula- Fig. 31. Mycoidea parasitica Cunningh. much 

magnified (after Marshall Ward). 

CG3.C. 

2. PHYCOPELTIS Millard. Disc a stratum one-cell thick, bearing seta, 

adnate to the lower surface of the leaf, yellow-green in colour. Phycopeltis 

(Fig. 32) has been identified as the gonidium of Strigula complanata in 

New Zealand and of Mazosia (Chiodectonaceae), a leaf lichen from tropical 

America. 

1 Deckenbach 1893. 

2 In a comparative study of leaf algae from Ceylon and Barbadoes, N. Thomas (1913) came to the 

conclusion that Marshall Ward's alga in its early stages is the same as Phyllactidium ti'opicum 

Moebius ; and that the Barbadoes alga with which she was working represented the older stages, it 

being then subcuticular in habit, forming rhizoids, barren and sterile aerial hairs and subcuticular 

zoosporangia.

6o CONSTITUENTS OF THE LICHEN THALLUS 

There is some confusion as to the genera of algae that form the gonidia 

of these epiphyllous lichens. Phyllactidium 

given by Zahlbruckner as the gonidium of 

all the Strigulaceae (except Strigula in 

part) is classified by de Toni 1 as probably 

synonymous with Phycopeltis Millard, and 

as differing from Mycoidea parasitica in the 

mode of growth. 

Fam. PRASIOLACEAE. Thallus filamen- 

Fig. 3,. Phycopeltis expansa Jenn. 

tous, often expanded into broad sheets by 

much magnified (after Vaughan the fusion of the filaments in one plane. 

Jennings). 

PRASIOLA Ag. Thallus filamentous, of one- to many-cell rows, or 

widely expanded (Fig. 33). The gonidium of Mastoidiaceae (Pyreno- 

carpeae). 

Fig. 33. Prasiola parietina Wille x 500 (after West). 

B. CHANGES INDUCED IN THE ALGA 

a. MYXOPHYCEAE. Though, as a general rule, the alga is less affected 

by its altered life-conditions than the fungus, yet in many instances it 

becomes considerably modified in appearance. In species of the genus 

Pyrenopsis small gelatinous lichens the alga is a Gloeocapsa very similar to 

G. magma. In the open it forms small colonies of blue-green cells surrounded 

by a gelatinous sheath which is coloured red with gloeocapsin. As a 

gonidium lying towards or on the outside of the granules composing the 

thallus, the red sheath of the cells is practically unchanged, so that the 

resemblance to Gloeocapsa is unmistakable. In the inner parts of the thallus, 

the colonies are somewhat broken up by the hyphae and the sheaths are not 

1 De Toni 1889.


only less evident but much more faintly coloured. In Synalissa, a minute 

shrubby lichen which has the same algal constituent, the tissue of the thallus 

is more highly evolved, and in it the red colour can barely be seen and 

then only towards the outside; at the centre it disappears entirely. The 

long chaplets of Nostoc cells persist almost unchanged in the thallus of the 

Collemaceae, but in heteromerous genera such as Pannaria and Peltigera 

they are broken up, or they are coiled together and packed into restricted 

areas or zones. The altered alga has been frequently described as Polycoccus 

punctiformis. A similar modification occurs in many cephalodia, so that the 

true affinity of the alga, in most instances, can only be ascertained after free 

cultivation. 

Bornet 1 has described in Coccocarpia molybdaea the change that the alga 

Scytonema undergoes as the thallus develops : in very young fronds the 

filaments of Scytonema are unchanged and are merely enclosed between 

layers of hyphae. At a later stage, with increase of the thallus in thickness, 

the algal filaments are broken up, their covering sheath disappears, and the 

cells become rounded and isolated. Petractis (Gyalecta) exanthematica has 

also a Scytonema as gonidium, and equally exact observations have been 

made by Funfstiick 2 on the way it is transformed by symbiosis: with the 

the thallus is immersed in the 

exception of a very thin superficial' layer, 

rock and is permeated by the alga to its lowest limits, 3 to 4 mm. below the 

surface, Petractis being a homoiomerous lichen. The Scytonema trichomes 

embedded in the rock become narrower, and the sheath, which in the 

epilithic part of the thallus is 4/4 wide, disappears almost entirely. The 

green colour of the cells fades and septation is less frequent and less regular. 

The filaments in that condition are very like oil-hyphae and can only be 

distinguished as algal by staining reagents such as alkanna. They never 

seem to be in contact with the fungal elements : there 

of parasitism nor even of consortism. 

is no visible appearance 

b. CHLOROPHYCEAE. As a rule the green-celled gonidium such as 

Protococcus is not changed in form though the colour may be less vivid, but 

in certain lichens there do occur modifications in its appearance. In Micarea 

(Biatorina) prasina, Hedlund 3 noted that the gonidium was a minute alga 

possessing a gelatinous sheath similar to that of a Gloeocapsa. He isolated 

the alga, made artificial cultures and found that, in the altered conditions, 

it gradually increased in size, threw off the gelatinous sheath and developed 

into normal Protococcus cells, measuring 7 to IO/LI in diameter. The gelatinous 

sheath was thus proved to be merely a biological variation, probably of 

value to the lichen owing to its capacity to imbibe and retain moisture. 

Zukal 4 also made cultures of this alga, but wrongly concluded it was a 

Gloeocystis, 


2 Fiinfstiick 1899. 

3 Hedlund 1892. 

4 Zukal 1895, p. 19.

62 


Moebius 1 has described the transformation from algae to lichen gonidia 

in a species epiphytic on Orchids in Porto Rico. He had observed that most 

of the leaves were inhabited by a membranaceous alga, Phyllactidium, and 

of a lichen thallus con- 

that constantly associated with it were small scraps 

taining isolated globose gonidia. The cells of the alga, under the influence 

of the invading fungus, were, in this case, formed into isolated round bodies 

which divided into four, each daughter-cell becoming surrounded by a 

membrane and being capable, in turn, of further division. 

Frank 2 followed the change from a free alga to a gonidium in Chroolepus 

(Trentepohlia) umbrinum, as shown in the hypophloeodal thalli of the 

Graphideae. The alga itself is frequent on beech bark, where it forms wide- 

spreading brownish-red incrustations consisting of short chains occasionally 

branched. The individual cells have thick laminated membranes and vary 

in width from 2Oyu, to 37/1. The free alga constantly tends to penetrate below 

and the immersed cells 

the cortical layers of the tree on which it grows, 

become not only longer and of a thinner texture, but the characteristic red 

colour so entirely disappears, that the growing penetrating apical cell may 

be light green or almost colourless. As a lichen gonidium the alga under- 

vanish and 

goes even more drastic changes : the red oily granules gradually 

the cells become chlorophyll-green or, if any retain a bright colour, they are 

orange or yellow. The branching of the chains is more regular, the cells 

more elongate and narrower; usually they are about 13 to 21/1, long and S/j, 

wide, or even less. Deeper down in the periderm, the chains become dis- 

integrated into separate units. Another notable alteration takes place in 

the cell-membrane which becomes thin and delicate. It has, however, been 

observed that if these algal cells reach the surface, owing to peeling of the 

bark, etc., they resume the appearance of a normal Trentepohlia. 

In certain cases where two kinds of algae were supposed to be present 

in some lichens, it has been proved that one species only is represented, the 

difference in their form being caused by mechanical pressure of the sur- 

rounding hyphae, as in Endocarpon and Staurothele where the hymenial 

gonidia are cylindrical in form and much smaller than those of the thallus. 

They were on this account classified by Stahl 8 under a separate algal genus, 

Stichococcus, but they are now known to be growth forms of Protococcus, the 

alga that is normally present in the thallus. Similar variations were found 

by Neubner 4 in the gonidia of the Caliciaceae, but, by culture experiments 

with the gonidia apart from the hyphae, he succeeded in demonstrating 

transition forms in all stages between the " Pleurococcus" cells and those of 

" 

Stichococcus" though the characters acquired by the latter are transmitted 

to following generations. The transformation from spherical to cylindrical 

i Moebius 1888. 

2 Frank 1876, p. 158. 

3 Stahl 1877. 

* Neubner 1893.


algal cells had been also noted by Krabbe 1 in the young podetia 

of some 

species of Cladonia, the change in form being due to the continued pressure 

in one direction of the parallel hyphae. 

Isolated algal cells have been observed within the cortex of various 

lichens. They are carried thither by the hyphae from the gonidial zone in 

the process of cortical formation, but they soon die off as in that position 

they are deprived of a sufficiency of air and of moisture. Forssell 2 found 

Xanthocapsa cells embedded in the hymenium of Omphalaria Heppii. They 

were similar to those of the thallus, but they were not associated with hyphae 

and had undergone less change than the thalline algae. 

C. CONSTANCY OF ALGAL CONSTITUENTS 

Lichen hyphae of one family or genus, as a rule, combine with the same 

species of alga, and the continuity of genera and species is maintained. 

There are, however, related lichens that differ chiefly or only in the characters 

of the gonidia. Among such closely allied genera or sections of genera may 

be cited Sticta with bright-green algae and the section Stictina with blue- 

gr-een; Peltidea similarly related to Peltigera and Nephroma to Nephromium. 

In the genus S0/orina,some of the species possess bright-green, others blue- 

green algae, while in one, 5. crocea*, there is an upper layer of small bright- 

green gonidia that project in irregular pyramids into the upper cortex ; 

while below these there stretches a more or less interrupted band of blue- 

green Nostoc cells. The two layers are usually separated by 

strands of 

hyphae, but occasionally they come into close contact, and the hyphal 

filaments pass from one zone to the other. In this genus cephalodia con- 

taining blue-green Nostoc are characteristic of all the "bright-green" species. 

Harmand 4 has recorded the presence of two different types of gonidia in 

Lecanora atra f. subgrumosa\ one of them, the normal Protococcus alga of the 

species, the other, pale-blue-green cells of Nostoc affinity. 

Forssell 5 states that in Lecanora (Psoroma) hypnorum, the normal bright- 

green gonidia of some of the squamules may be replaced by Nostoc. In that 

case they are regarded as cephalodia, though in structure they exactly 

resemble the squamules of Pannaria pezizoides, and Forssell considers that 

there is sufficient evidence of the identity of the hyphal constituent in these 

two lichens, the alga alone being different. 

It may be that in Archilichens with a marked capacity to form a second 

symbiotic union with blue-green algae, a tendency to revert to a primitive 

condition is evident a condition which has persisted wholly in Peltigera 

with its Nostoc zone, but is manifested only by cephalodia formation in the 

1 Krabbe 1891. 

2 3 

Forssell 1885. Hue 1910. 

5 Forssell 1886. 

* Harmand 1913, p. 1050.

64 


Peltidea section of the genus. In this connection, however, we must bear in 

mind Forssell's view that it is the Archilichens that are the more primitive 1 . 

The alien blue-green algae with their gelatinous sheaths are adapted to 

the absorption and retention of moisture, and, in this way, they doubtless 

render important service to the lichens that harbour them in cephalodia. 

D. DISPLACEMENT OF ALGAE WITHIN THE THALLUS 

a. NORMAL DISPLACEMENT. Lindau 2 has contrasted the advancing 

apical growth of the creeping alga Trentepohlia with the stationary condition 

of the unicellular species that multiply by repeated division or by sporulation, 

and thus form more or less dense zones and groups of gonidia in most 

lichens. The fungus in the latter case pushes its way among the algae and 

breaks up the compact masses by a shoving movement, thus letting in light 

and air. The growing hypha usually applies itself closely round an algal 

cell, and secondary branches arise which in time encircle it in a network of 

short cells. In the thallus of Variolaria* the hyphae from the lower tissues, 

termed push-hyphae by Nienburg 4 

, push their way into the algal groups and 

filaments composed of short cells come to lie closely round the individual 

gonidia. Continued growth is centrifugal, and the algae are carried outward 

with the extension of the hyphae (Fig. 12). Cell-division is more active at the 

periphery, that being the area of vigorous growth, and the algal cells are, in 

consequence, generally smaller in that region than those further back, the 

latter having entered more or less into a resting condition, or, as is more 

probable, these smaller cells are aplanospores not fully mature. 

b. LOCAL DISPLACEMENT. Specimens of Parmelia physodes were found 

several times by Bitter, the grey-green surface of which was marbled with 

whitish lines, caused by the absence of gonidia under these lighter-coloured 

areas. The thallus was otherwise healthy as was manifested by the freely 

fruiting condition : no explanation of the phenomenon was forthcoming. 

Bitter compared the condition with the appearance of lighter areas on the 

thallus of Parmelia obscurata. 

Something of the same nature was observed on the thallus of a Peltigera 

collected by F. T. Brooks near Cambridge. The marking took the form of 

a series of concentric circles, starting from several centres. The darker lines 

were found on examination to contain the normal blue-green algal zone, 

while the colour had faded from the lighter parts. The cause of the difference 

in colouration was not apparent. 

1 See Chap. VII. 2 Lindau 1895. 


4 

Nienburg 1917.

LICHEN ALGAE 

E. NON-GONIDIAL ORGANISMS ASSOCIATED WITH LlCHEN HYPHAE 

Bonnier 1 made a series of cultures with lichen spores and green cells 

other than those that form lichen gonidia. In one instance he substituted 

Protococcus botryoides for the normal gonidia of Parmelia (Xanthoria) 

parietina\ in another of his cultures he replaced Protococcus viridis by the 

filamentous alga Trentepolilia abietina. In both cases the hyphae attached 

themselves to the green cells and a certain stage 

of thallus formation was reached, though growth 

ceased fairly early. Another experiment made 

with the large filaments of Vaucheria sessilis met 

with the same amount of success (Fig. 34). The 

germinating hyphae attached themselves to the 

alga and grew all round it, but there was no advance 

to tissue formation. 

Cultures were also made with the protonema 

of mosses. Either spores of mosses and lichens 

were germinated together, or lichen spores were 

sown in close proximity to fully formed protonemata. 

The developing hyphae seized on the 

moss cells and formed a network of branching 

anastomosing filaments along the whole length of 

the protonema without, however, penetrating the 

cells. If suitable algae were encountered, proper 

thallus formation commenced, and Bonnier considers 

that the hyphae receive stimulus and 

nourishment from the protonema sufficient to 

tide them over a considerable period, perhaps until the algal symbiont is 

met. An interesting variation was noted in connection with the cultures of 

Mnium hornum*. If the protonema were of the usual vigorous type, the 

whole length was encased by the hyphal network; but if it were delicate and 

slender, the protoplasm collected in the cell that was touched by hyphae 

and formed a sort of swollen thick-walled bud (Fig. 35). This new body 

persisted when the rest of the filament and the hyphae had disappeared, 

and, in favourable conditions, grew again to form a moss plant. 

F. PARASITISM OF ALGAE ON LICHENS 

g. 34. Germinating hyphae of 

Lecanora subfusca Ach. , growing 

over the alga Vaucheria 

sessilis DC., much magnified 

(after Bonnier). 

A curious instance of undoubted parasitism by an alga, not as in 

Strigula on one of the higher plants, but on a lichen thallus, is recorded 

group of Protococcns-\ti


of Peltigera had found their way into the tissue, the underlying cortical 

cells having degenerated. The blue-green cells of the normal gonidial layer 

Fig. 35. Pure culture of protonema of Mnium hornum L. with spores and hyphae of 

Lecidea vernalis Ach. a,a,a, buds forming x 150 (after Bonnier). 

had died off before their advance but no zone was formed by the invading 

algae; they simply withdrew nourishment and gave seemingly no return. 

The phenomenon is somewhat isolated and accidental but illustrates the 

capacity of the alga to absorb food supply from lichen hyphae. 

An instance of epiphytic growth has also been recorded by Zahlbruckner 1 . 

He found an alga, Trentepohlia abietina, covering the thallus of a Brazilian 

lichen, Parmelia isidiophora, and growing so profusely as to obscure the 

isidiose character towards the centre of the thallus. There was no genetic 

connection of the alga with the lichen as the former was not that of the 

lichen gonidium. Lichen thalli are indeed very frequently the habitat of 

green algae, though their occurrence may be and probably 

* Zahlbruckner 1902. 

is accidental,

CHAPTER III 

MORPHOLOGY 

GENERAL ACCOUNT OF LICHEN STRUCTURE 

I. ORIGIN OF LICHEN STRUCTURES 

THE two organisms, fungus and alga, that enter into the composition of the 

lichen plant are each characterized by the simplicity of their original structure 

in which there is little or no differentiation into tissues. The gonidia-forming 

algae are many of them unicellular, and increase mainly by division or by 

sporulation into daughter-cells which become rounded off and repeat the life 

of the mother-cell ; others, belonging to different genera, are filaments, 

mostly of single cell-rows, with apical growth. The hyphal elements of the 

lichen are derived from fungi in which the vegetative body is composed of 

branching filaments, a character which persists in the lichen thallus. 

The union of the two symbionts has stimulated both, but more especially 

the fungus, to new developments of vegetative form, in which the fungus, as 

the predominant partner, provides the framework of the lichen plant-body. 

Varied structures have been evolved in order to secure life conditions favour- 

as the 

able to both constituents, though more especially to the alga ; and 

close association of the assimilating and growing tissues is maintained, the 

thallus thus formed is capable of indefinite increase. 

A. FORMS OF CELL-STRUCTURE 

There is no true parenchyma or cellular structure in the lichen thallus 

such as forms the ground tissue of the higher 

plants. The fungal hyphae are persistently filamentous 

and either simple or branched. By 

frequent and regular cell-division always at right 

angles to the long axis and by coherent growth, 

a pseudoparenchyma may however be built up 

which functions either as a protective or strength- 

Lindau 1 

proposed the name "plectenchyma" 

for the tangled weft of hyphae that is the prin- 

J r 

>^^^P S K?S3^3^- 

Fig. 36. Vertical section of 

cipal tissue system in fungi as well as lichens. young stage of stratose thai- 

The more elaborated pseudoparenchyma he desig- & ^JjSjgSS 

nates as "paraplectenchyma," while the term cortex ; 6, medullary hyphae ; 

, , , i r i /- 1 c< gonidial zone, x 500 (after 

prosoplectenchyma he reserved for the fibrous Schwendener). 

1 Lindau 1899. 

52

68 

MORPHOLOGY 

or chondroid strands of compact filaments that occur frequently 

in the 

thallus of the larger fruticose lichens, and are of service in strengthening 

the fronds. The term plectenchyma is now generally used for pseudo- 

parenchyma. 

B. TYPES OF THALLUS 

1 

Three factors, according to Reinke have been of influence in , determining 

the thalline development. The first, and most is important, the necessity to 

There is 

provide for the work of photosynthesis on the part of the alga. 

also the building up of a tissue that should serve as a storage of reserve 

material, essential in a plant the existence of which is prolonged far beyond 

the natural duration of either of the component organisms; and, finally, 

there is the need of protecting the long-lived plant as a whole though more 

particularly the alga. 

Wallroth was the first to make a comparative study of the different 

lichen thalli. He distinguished those lichens in which the green cells and 

the colourless filaments are interspersed equally through the entire thallus 

as "homoiomerous" (Fig. 2), and those in which there are distinct layers of 

cortex, gonidia, and medulla, as "heteromerous" (Fig. i), terms which, 

though now considered of less importance in classification, still persist 

and are of service 

general 

in describing the position of the alga with regard to the 

structure. A less evident definition of the different types of thallus 

has been proposed by Zukal 2 who divides them into "endogenous" and 

"exogenous." 

a. ENDOGENOUS THALLUS. The term has been applied to a compara- 

tively small number of homoiomerous lichens in which the alga predominates 

in the development, and determines the form of the thallus. These algae, 

members of the Myxophyceae, are extremely gelatinous, and the hyphae 

grow alongside or within the gelatinous sheath. In the simpler forms the 

vegetative structure is of the most primitive type: the alga retains its 

original character almost unchanged, and the ascomycetous fungus grows 

along with and beside it (Fig. 4). Such are the minutely tufted thalli of 

Thermutis and Spilonema and the longer strands of Epkebe, in which the 

associated Scytonema or Stigonema, filamentous blue-green algae, though 

excited to excessive growth, scarcely lose their normal appearance, making 

it difficult at times to recognize the lichenoid character unless the fruits also 

are present. 

Equally primitive in most cases is the structure of the thallus associated 

with Gloeocapsa. The resulting lichens, Pyrenopsis, Psorotichia, etc. are 

simply gelatinous crusts of the alga with a more or less scanty intermingling 

of fungal hyphae. 

1 Reinke 1895. 

2 Zukal l895> p . gfo.

ORIGIN OF LICHEN STRUCTURES 69 

In the Collemaceae, the gonidial cells of which are species of Nostoc 

(Fig. 2), there appears a more developed thallus; but in general, symbiosis 

in Collema has wrought the minimum of change in the habit of the alga, 

hence the indecision of the earlier botanists as to the identification and 

classification of Nostoc and Collema. Though in many of the species of the 

genus Collema no definite tissue is formed, yet, under the influence of 

symbiosis, the plants become moulded into variously shaped lobes which 

are specifically constant. In some species there is an advance towards 

more elaboration of form in the protective tissues of the apothecia, a layer 

of thin-walled plectenchyma being occasionally formed beneath or around 

the fruit as in Collema granuliferum. 

In all these lichens, it is only the thallus that can be considered as 

primitive: the fruit is a more or less open apothecium more rarely a perithecium 

with a fully developed hymenium. Frequently it is provided with 

a protective thalline margin. 

b. EXOGENOUS THALLUS. In this group, composed almost exclusively 

of heteromerous lichens, Zukal includes all those in which the fungus takes 

the lead in thalline development. He counts as such Leptogium, a genus 

closely allied to Collema but with more membranous lobes, in which the 

short terminal cells of the hyphae have united to form a continuous cortex. 

A higher development, therefore, becomes at once apparent, though in some 

genera, as in Coenogonium, the alga still predominates, while the simplest 

forms may be merely a scanty weft of filaments associated with groups of 

algal cells. Such a thallus is characteristic of the Ectolechiaceae, and some 

Gyalectaceae, etc., which have, indeed, been described 

1 

by Zahlbruckner 

as homoiomerous though their gonidia belong to the non-gelatinous 

Chlorophyceae. 

Heteromerous lichens have been arranged by Hue 2 

according to their 

general structure in three great 

series : 

1. Stratosae. Crustaceous, squamulose and foliose lichens with a 

dorsiventral thallus. 

2. Radiatae. Fruticose, shrubby or filamentous lichens with a strap- 

shaped or cylindrical thallus of radiate structure. 

3. Stratosae-Radiatae. Primary dorsiventral thallus, either crustaceous 

or squamulose, with a secondary upright thallus of radiate structure called 

the podetium (Cladoniaceae). 

1 Zahlbruckner 1907. 

2 Hue 1899.

;o 

MORPHOLOGY 

II. STRATOSE THALLUS 

i. CRUSTACEOUS LICHENS 

A. GENERAL STRUCTURE 

In the series "Stratosae," the plant is dorsiventral, the tissues forming 

the thallus being arranged more or less regularly in strata one above the 

other (Fig. 37). On the upper surface there is a hyphal layer constituting 

Fig. 37. Vertical section of crustaceous lichen (Lecanora subfusca 

var. chlarona Hue) on bark, a, lichen cortex; b, gonidia; 

c, cells of the periderm. 

x 100. 

a cortex, either rudimentary or highly elaborated ; beneath the cortex is . 

situated the gonidial zone composed of algae and hyphae in close association 

; and deeper down the medulla, generally a loose tissue of branching 

hyphae. The lower cortex which abuts on the medulla be absent. 

may be as fully 

developed as the upper or it may 

The growing tissue is chiefly marginal ; the hyphae on the outer edge 

remain "meristematic" 1 and provide for horizontal as well as vertical ex- 

tension; and there is also continual increase of the algal cells. There is in 

addition a certain amount of intercalary growth due to the activity of the 

gonidial tissue, both algal and fungal, providing for the renewal of the 

cortex, and even interposing new tissue. 

B. SAXICOLOUS LICHENS 

a. EPILITHIC LICHENS, The crustaceous lichens forming this group 

spread over the rock surfaces. The support must be stable to allow the 

necessary time for the slowly developing organism, and therefore rocks that 

are friable or subject to continual weathering are bare of lichens. 

aa. Hypothallus or Prothallus. The first stage of growth in the lichen 

thallus can be most easily traced in epilithic crustaceous species, especially 

in those that inhabit a smooth rock surface. The spore, on germination, 

produces a delicate branching septate mycelium which radiates on all sides, 

as was so well observed and recorded by Tulasne 2 in Verrucaria muralis 

(Fig. 14). Zukal 3 has called this first beginning the prothallus. In time the 

1 Wainio has adopted this term for growing hyphae 1897, p. 33. 

2 Tulasne 1852. 3 Zukal lg 

I

STRATOSE THALLUS 

cell-walls of the filaments become much thicker and though, in some species, 

they remain colourless, in others they become dark-coloured, all except the 

extreme tips, owing to the presence of lichen pigments a provision, Zukal 1 

considers, to protect them against the ravages of insects, etc. The pro- 

thallic filaments adhere - 

closely to the substratum and the branching 

becomes gradually more dendroid in form, though sometimes hyphae are 

united into strands, or even form a kind of plectenchymatous tissue. This 

purely hyphal stage may persist for long 

periods without much change. In time 

there may be a fortuitous encounter with 

the algae (Fig. 38 A) which become the 

gonidia of the plant. Either these have 

been already established on the substratum 

as free-growing organisms, or, as 

accidentally conveyed, they alight on the 

prothallus. The contact between alga 

and hypha excites both to active growth 

and to cell-division; and the rapidly 

multiplying gonidia are as speedily surrounded 

by the vigorously growing hyphal 

filaments. 

Schwendener 2 has thus described the 

origin and further development of prothallus 

and gonidia: on the dark-coloured 

proto- or prothallus, he noted small nestling groups of green 

cells which 

he, at that time, regarded as direct outgrowths from the lichen hyphae. 

These gonidial cells, increasing by division, multiplied gradually and 

gathered into a connected zone. He also observed that the hyphae in 

contact with the gonidia became more thin-walled and produced many new 

branches. Some of these newly formed branches grow upwards and form 

the cortex, others grow downwards and build up the medulla or pith; the 

filaments at the circumference continue to advance and may start new 

centres of gonidial activity (Fig. 386). In many species, however, this 

prothallus or, as it is usually termed at this stage, the hypothallus, becomes 

very soon overgrown and obscured by the vigorous increase of the 

first formed symbiotic tissue and can barely be seen as a white or dark line 

bordering the thallus (Fig. 39). Schwendener 3 has stated that probably 

only lichens that develop from the spore are distinguished by a proto- 

thallus, and that those arising from soredia do not form these first creeping 

filaments. 

Zukal 1895. 


Fig. 38 A. Hypothallus of Rhizocarpon 

confervoides DC., from the extreme edge, 

with loose gonidia x 600. 

3 Schwendener 1863.

72 

MORPHOLOGY 

bb. Formation of crustaceous tissues. Some crustaceous lichens have 

a persistently scanty furfuraceous crust, the vegetative development never 

advancing much beyond the first rather loose association of gonidia and 

Fig. 38 B. Young thallus of Rhizocarpon confervoides DC., with various 

centres of gonidial growth on the hypothallus x 30. 

Fig. 39. Lecanora parella Ach. Determinate thallus with white bordering 

hypothallus, reduced (M. P., Photo.).

hyphae ; 

STRATOSE THALLUS 73 

but in those in which a distinct crust or granules are formed, three 

different strata of tissue are discernible: 

1st. An upper cortical tissue of interlaced hyphae with frequent septation 

and with swollen gelatinous walls, closely compacted and with the 

lumen of the cells almost obliterated, not unfrequently a layer of mucilage 

serving as an outer cuticle. This type of cortex has been called by Hue 1 

"decomposed." It is subject to constant surface weathering, thin layers 

being continually peeled off, but it is as continually being renewed endo- 

genously by the upward growth of hyphae from the active gonidial zone. 

Exceptions to this type of cortex in crustaceous lichens are found in some 

Pertusariae where a secondary plectenchymatous cortex is formed, and in 

Dirina where it is fastigiate 2 as in Roccella. 

2nd. The gonidial zone a somewhat irregular layer of algae and 

hyphae below the cortex which varies in thickness according to the species. 

3rd. The medullary tissue of somewhat loosely intermingled branching 

hyphae, with generally rather swollen walls and narrow lumen. It rests 

directly on the substratum and follows every inequality and crack so 

closely, even where it does not penetrate, that the thallus cannot be 

detached without breaking it away. 

In Verrucaria mucosa, a smooth brown maritime lichen found on rocks 

between tide-levels, the thallus is composed of tightly packed vertical rows 

of hyphae, slender, rather thin-walled, and divided into short cells. The 

gonidia are chiefly massed towards the upper surface, but they also occur in 

vertical rows in the medulla. One or two of the upper cells are brown and 

form an even cortex. The same formation occurs in some other sea-washed 

species; the arrangement of the tissue elements recalls that of crustaceous 

Florideae such as Hildenbrandtia, Cruoria, etc. 

cc. Formation of areolae. An "areolate" thallus is seamed and scored 

which divide it 

by cracks of varying width and depth 

into minute compartments. These cracks or fissures or 

chinks originate in two ways depending on the presence 

or absence of hypothallic hyphae. Where the hypothallus 

is active, new areolae arise when the filaments encounter 

new groups of algae. More vigorous growth starts at once 

and proceeds on all sides from these algal centres, until 

similarly 

Fig. 40. Young 

formed areolae are met, a more or less prothallus of Rhizonounced 

fissure marking the limits of each. This primary 

areolation, termed rimose or rimulose, is well seen in the 

S^rfc^^'kh 

primary and sub- 

thin smooth thallus of Rhizocarpon geographicum (Fig. 40); 

but the first-formed areolae are also very frequently slightly 

1 Hue 1906. 

2 See p. 83. 

x 5-

74 

MORPHOLOGY 

marked by subsequent cracks due to unequal growth. The areolation caused 

by primary growth conditions tends to become gradually less obvious or to 

disappear altogether. 

Secondary areolation is due to unequal intercalary growth of the 

otherwise continuous thallus 1 . A more active increase of any minute portions 

provokes a tension or straining of the cortex between the swollen areas 

and the surrounding more sluggish tissues ; the surface layers give 

way and chinks arise, a condition described by older lichenologists as 

"rimose-diffract" or sometimes as "rhagadiose." The thallus is generally 

thicker, more broken and granular in the older central parts of the lichen. 

Towards the circumference, where the tissue is thinner and growth more 

equal, the chinks are less evident. Sometimes the more vigorously growing 

areolae may extend over those immediately adjoining, in which case the 

covered portions become brown and their gonidia gradually disappear. 

Strongly marked intersecting lines, similar to those round the margin 

of the thallus, are formed when hypothalli that have themselves started 

from different centres touch each other. A large continuous patch of 

crustaceous thallus may thus be composed of many individuals (Fig. 41). 

Fig. 41. Rhizocarpon geographicum DC. on boulder, reduced (M.P., Photo.}. 

b. ENDOLITHIC LICHENS. In many species, only the lower hyphae 

penetrate the substratum either of rock or soil. In a few, more especially 

those growing on limestone, the greater part or even the whole of the vegetative 

thallus and sometimes also the fruits are, to some extent, immersed 

1 

Malinowski 1911.


in the rock. It has now been demonstrated that a number of lichens, 

formerly described as athalline, possess a considerable vegetative body 

which cannot be examined until the limestone in which they are embedded 

is dissolved by acids. One such species, Petractis (Gyalecta) exanthematica, 

studied by Steiner 1 and later by Funfstuck 2 

, is associated with the blue- 

green filamentous alga, Scytonema, and is homoiomerous in structure, the 

alga growing through and permeating the whole of the embedded thallus. 

A partly homoiomerous thallus, associated with Trentepohlia, has been 

described by Bachmann 3 . He found the bright-yellow filaments of the 

alga covering the surface of a calcareous rock. By reason of their apical 

growth, they pierced the rock and dissolved a way for themselves, not only 

among the loose particles, but right through a clear calcium crystal reaching 

generally to a depth of about 200 /u, though isolated threads had gone 350/1* 

below the surface. Near the outside the tendency was for the algae to 

become stouter and to increase by intercalary growth and by budded yeastlike 

outgrowths; lower down they were somewhat smaller. The hyphae 

that became united with the algae were unusually slender and were charac- 

terized by frequent anastomoses. They closely surrounded the gonidia 

and also filled the loose spaces of the limestone with their fine thread-like 

strands. Though oil was undoubtedly present in the lower hyphae there 

were no swollen nor sphaeroid cells 4 . Some interesting experiments with 

moisture proved that the part of the rock permeated with the lichen 

absorbed much more water and retained it longer than the part that was 

lichen-free. 

Generally 

the embedded tissues follow the same order as in other 

crustaceous lichens : an upper layer of cortical hyphae, next a gonidial 

zone, and beneath that an interlaced tissue of medullary or rhizoidal hyphae 

which often form fat-cells 4 . Friedrich 5 has given measurements of the 

immersed thallus of Lecanora (Biatorella) simplex: under a cortical layer of 

hyphae there was a gonidial zone 600-700/4 thick, while the lower hyphae 

reached a depth of 1 2 mm. ; 

reaching 

he has also recorded an instance of a thallus 

a depth of 30 mm. 

On siliceous rocks such as granite, rhizoidal hyphae penetrate the rock 

chiefly between the thin separable flakes of mica. Bachmann 6 has recognized 

in these conditions three distinct series of cell-formations: (i) slender 

long-celled sparsely branched hyphae which form a network by frequent 

anastomoses; (2) further down, though only occasionally, hyphae with 

short thick-walled bead-like cells; and (3) beneath these, but only in or 

near mica crystals, spherical cells containing oil or some albuminous 

substance. 

1 Steiner r88i. 

4 See p. 215. 

2 Funfstuck 1899. 

5 Friedrich 1906. 


' Bachmann 1907.

;6 

MORPHOLOGY 

c. CHEMICAL NATURE OF THE SUBSTRATUM. Lichens growing on 

calcareous rocks or soils are more or less endolithic, those on siliceous 

rocks are largely epilithic, but Bachmann 1 found that the mica crystals in 

granite were penetrated, much in the same way as limestone, by the lichen 

hyphae. These travel through the mica in all directions, though they tend 

to follow the line of cleavage, thus taking the direction of least cohesion. 

He found that oil-hyphae were formed, and also certain peculiar bristle-like 

terminal branches; in other cases there were thin layers of plectenchyma, and 

gonidia were also present. 

If however felspar or quartz crystals, no matter 

how thin, blocked the way, further growth was arrested, the hyphae being 

unable to pierce through or even to leave any trace on the quartz 2 . On 

granite containing no mica constituents the hyphae can only follow the 

cracks between the different impenetrable crystals. 

Stahlecker 3 has confirmed Bachmann's observations, but he considers 

that the difference in habit and structure between the endolithic and 

epilithic series of lichens is due rather to the chemical than to the physical 

nature of the substratum. Thus in a rock of mixed composition such as 

granite, the more basic constituents are preferred by the hyphae, and are 

the first to be surrounded: mica, when present, is at once penetrated; 

particles of hornblende, which contain 40 to 50 per cent, only of silicic 

acid, are laid hold of by the filaments of the lichen before the felspar, of 

which the acid content is about 60 per cent.; quartz grains which are pure 

silica are attacked last of all. though in the course of time they also become 

corroded. 

The character of the substratum also affects to a great extent the 

comparative development of the different thalline layers: the hyphal tissues 

in silicicolous lichens are much thinner than in lichens on limestone, and 

the gonidial zone is correspondingly wider. In a species of Staurothele on 

granite, Stahlecker 3 estimated the gonidial zone to be about 600/1, thick, 

while the lower medullary hyphae, partly burrowing into the rock, measured 

about 6 mm. Other measurements at different parts of the thallus gave a 

rhizoidal depth of 3 mm., while on a more finely granular substratum, with 

a gonidial zone of 350 p, the rhizoidal hyphae measured only imm. On 

calcareous rocks, on the contrary, with a gonidial zone that is certainly no 

larger, the hyphal elements penetrate the rock to varying depths down to 

1 5 mm. or even more. 

Lang 4 

has recorded equally interesting measurements for Sarcogyne 

(Biatorelld) latericola: on slaty rock which contained no mixture of lime, 

the gonidial zone had a thickness of 80 //,, a considerable proportion of the 

very thin thallus. Funfstiick 5 has indeed suggested that this lichen on acid 


4 

Lang 1903. 


B Funfstiick 1899. 

3 Stahlecker 1906.

STRATQSE THALLUS 77 

rocks is only a starved condition of Sarcogyne (Biatorella) simplex, which on 

calcareous rocks, though with a broader gonidial zone, has, as noted above, 

a correspondingly much larger hyphal tissue. 

Stahlecker's theory is that the hyphae require more energy to grow in 

the acid conditions that prevail in siliceous rocks, and therefore they make 

larger demands on the algal symbionts. It follows that the latter must be 

stimulated to more abundant growth than in circumstances favourable to 

the fungus, such as are found in basic (calcareous) rocks; he concludes that 

on the acid (siliceous) rocks, the epilithic or superficial condition is not only 

a physical but a biological necessity, to enable the algae to grow and 

multiply in a zone well exposed to light with full opportunity for active 

photosynthesis and healthy increase. 

C. CORTICOLOUS LICHENS 

The crustaceous lichens occurring on bark or on dead wood, like those 

on rocks, are either partly or wholly immersed in the substratum (hypophloeodal), 

or they grow on the surface (epiphloeodal); but even those with 

a superficial crust are anchored by the lower hyphae which enter any crack 

or crevice of wood or bark and so securely attach the thallus, that it can 

only be removed by cutting away the underlying substance. 

a. EPIPHLOEODAL LICHENS. These lichens originate in the same way 

as the corresponding epilithic series from soredia or from germinating 

spores, and follow the same stages of growth; first a hypothallus with 

subsequent colonization of gonidia, the formation of granules, areolae, etc. 

The small compartments are formed as primary or secondary areolae; the 

larger spaces are marked out by the encounter of hypothalli starting from 

different centres. 

The thickness of the thallus varies considerably according to the species. 

In some Pertusariae with a stoutish irregular crust there is a narrow 

amorphous cortical layer of almost obliterated cells, a thin gonidial zone 

about 35/4 in width and a massive rather dense medulla of colourless 

hyphae. Darbishire 1 has described and figured in Varicellaria microsticta, 

one of the Pertusariaceae, single hyphae that extend like beams across the 

wide medulla and connect the two cortices. In some Lecanorae and Lecideae 

there is, on the contrary, an extremely thin thallus consisting of groups of 

algae and loose fungal filaments, which grow over and between the dead 

cork cells of the outer bark. On palings, there is often a fairly substantial 

granular crust present, with a gonidial zone up to about So/* thick, while 

the underlying or medullary hyphae burrow among the dead wood fibres. 

1 Darbishire 1897.

78 

MORPHOLOGY 

b. HYPOPHLOEODAL LICHENS. These immersed lichens are compar- 

able with the endolithic species of the rock formations, as their thallus is 

almost entirely developed under the outer bark of the tree. They are recog- 

nizable, even in the absence of any fructification, by the somewhat shining 

brownish, white or olive-green patches that indicate the underlying lichen. 

This type of thallus occurs in widely separated families and genera, Lecidea, 

Lecanora, etc., but it is most constant in Graphideae and in those Pyreno- 

lichens of which the algal symbiont belongs to the genus Trentepohlia, 

The development of these lichens is of peculiar interest as it has been 

proved that though both symbionts are embedded in the corky tissues, the 

hyphae arrive there first, and, at some later stage, are followed by the 

gonidia. There is therefore no question of the alga being a "captured 

slave" or "unwilling mate." 

Frank 1 made a thorough study of several subcortical forms. He found 

that \nArthonia radiata, the first outwardly visible indication of the presence 

of the lichen on ash bark was a greenish spot quite distinct from the 

normal dull-grey colour of the periderm. Usually the spots are round in 

outline, but they tend to become ellipsoid in a horizontal direction, being 

influenced by the growth in thickness of the tree. At this early stage only 

hyphae are present; Bornet 2 as well as Frank described the outer periderm 

cells as penetrated and crammed with the colourless slender filaments. 

Lindau 3 

in a more recent work, , 

disputes that statement: he found that the 

hyphae invariably grew between the dead cork cells, splitting them up and 

disintegrating the bark, but never piercing the membranes. The purely 

prothallic condition, as a weft of closely entangled hyphae, may last, Frank 

considers, for a long period in an almost quiescent condition possibly for 

several years before the gonidia arrive. 

It is always difficult to observe the entrance of the gonidia but they 

seem to spread first under the second or third layers of the periderm. With 

care it is possible to trace a filament of Trentepohlia from the surface down- 

wards, and to see that the foremost cell is really the growing and advancing 

apex of the creeping alga. Both symbionts show increased vigour when 

they encounter each other: the thallus at once develops in extent and in 

depth, and, ultimately, reproductive bodies are formed. In some species the 

apothecia or perithecia alone emerge above the bark, 

in others the outer 

peridermal cells are thrown off, and the thallus thus becomes superficial to 

some extent as a white scurfy or furfuraceous crust. 

The change from a hypophloeodal to a partly epiphloeodal condition 

depends largely on the nature of the bark. Frank 1 found that Lecanora 

pallida remained for a long time immersed when growing on the thick 

rugged bark of oak trunks. When well lighted, 

1 Frank 1876. 

2 Bornet 1873, p. 81. 

or on trees w'ith a thin 

3 Lindau 1895.

STRATOSE^THALLUS 

periderm, such as the ash, the lichen emerges much earlier and becomes 

superficial. 

Black (or occasionally white) lines intersect the thallus and mark, as in 

saxicolous lichens (Fig. 41), the boundary lines between different indi- 

viduals or different species. The pioneer hyphae of certain lichens very 

frequently become dark-coloured, and Bitter 1 has suggested as the reason 

for this that in damp weather the hypothallic growth is exceptionally 

vigorous. When dry weather supervenes, with high winds or strong sun- 

shine, the outlying hyphae, unprotected by the thallus, become dark- 

coloured. On the return of more normal conditions the blackened tips are 

thrown off. Bitter further states that species of Graphideae do not form a 

permanent black limiting line when they grow in an isolated position: 

only when their advance is checked by some other thallus that the dark persistent 

edge appears, a characteristic also to be seen in the crust of other 

lichens. The dark boundary is always more marked in sunny exposed 

situations: in the shade, the line is reduced to a mere thread. 

Bitter's restriction of black boundary lines to cases of encountering 

thalli only, would exclude the comparison one is tempted to make between 

the advancing hyphae of lichens and those of many woody fungi where the 

extreme edge of the white invaded woody tissue is marked by a dark line. 

In the latter case however it is the cells of the host that are stained black 

by the fungus pigment. 

2. SQUAMULOSE LICHENS 

A. DEVELOPMENT OF THE SQUAMULE 

The crustaceous thallus is more or less firmly adherent to, or confused 

with, the substratum. Further advance to a new type of thallus is made 

when certain hyphal cells of soredium or granule take the lead in an 

ascending direction both upwards and outwards. As growth becomes 

definitely apical or one-sided, the structure rises free from the substratum, 

and small lobules or leaflet-like squamules are formed. Each squamule 

in this type of thallus is distinct in origin and not merely the branch of 

a larger whole. 

In a few lichens the advance from the crustaceous to the squamulose 

structure is very slight. The granules seem but to have been flattened out 

at one side, and raised into minute rounded projections such as those that 

compose the thallus of Lecanora badia generally described as "subsquamu- 

lose." The squamulose formation is more pronounced in Lecidea ostreata, 

and the whole thallus may finally consist 

and in some species of Pannaria ; 

of small separate lobes as in Lecidea lurida, Lecanora crassa, L. saxicola, 

1 Bitter 1899. 

79 

it is

8o 

MORPHOLOGY 

species of Dermatocarpon and the primary thallus of the Cladoniae. Most of 

these squamules are of a firm texture and more or less round in outline; in 

some species of Cladonia, etc., they are variously crenate, or cut into pinnatelike 

leaflets. Squamulose lichens grow mostly on rocks or soil, occasionally on 

dead wood, and are generally attached by single rhizoidal hyphae, either 

produced at all points of the under surface, or from the base only, growth 

in the latter case being one-sided. In a few instances, as in Heppia Guepint, 

there is a central hold-fast. 

A frequent type of squamulose thallus is that termed "placodioid," or 

"effigurate," in which the squamulose character is chiefly apparent at the 

circumference. The thallus is more or less orbicular in 

the centre may be squamulose or granular and 

Fig. 42. Placodium 

murorum DC. 

Part of placodioid 

thallus with apothecia 

x i. 

outline ; 

cracked into areolae ; the outer edge is composed of 

radiating lobules closely appressed 

to the substratum 

(Fig. 42). 

All lichens with this type of thallus were at one time 

included in the genus Placodium, now restricted by some 

lichenologists to squamulose or crustaceous species with 

polarilocular spores. Many of them rival Xanthoria parietina 

brilliant yellow colouring. 

Fl 'g- 43- Lecania candicans A. Zahlbr., with placodioid thallus, 

reduced (S. H., Photo.}. 

in their 

There are also greyish-white effigurate lichens such as Lecanora saxicola, 

Lecania candicans (Fig. 43) and Buellia canescens, well-known British 

species.


B. TISSUES OF SQUAMULOSE THALLUS 

The anatomical structure of the squamules is in general somewhat 

similar to that of the crustaceous thallus: an upper cortex, a gonidial zone, 

and below that a medullary layer of loose hyphae with sometimes a lower 

cortex. 

1. The upper cortex, as in crustaceous lichens, is generally 

of the 

"decomposed" 1 or amorphous type: interlaced hyphae with thick gelatinous 

walls. A more highly developed form is apparent in Parmeliella and 

Pannaria where the upper cortex is formed of plectenchyma, while in the 

squamules of Heppia the whole structure is built up of plectenchyma, with 

the exception of a narrow band of loose hyphae in the central pith. 

2. The gonidia are Myxophyceae or Chlorophyceae ; the squamules in 

some instances may be homoiomerous as in Lepidocollema, but generally 

they belong to the heteromerous series, with the gonidia in a circumscribed 

zone, and either continuous or in groups. Friedrich 2 held that, as in crustaceous 

lichens the development of the gonidial as compared with the other 

tissues depended on the substratum. The squamules of Pannaria micro- 

phylla on sandstone were lOOyu- thick, and the gonidial layer occupied 80 or 

that may be compared Placodium Garovagli on 

90 /A of the whole 3 . With 

lime-containing rock: the gonidial layer measured only 50 //. across, the 

pith hyphae 280 p and the rhizoidal hyphae that penetrated the rock 500 //.. 

3. 

The medullary layer, as a rule, is of closely compacted hyphae which 

give solidity to the squamules; in those of Heppia it is almost entirely 

formed of plectenchyma. 

4. The lower cortex is frequently little developed or absent, especially 

when the squamules are closely applied to the support as in some species 

of Dennatocarpon. In some of the squamulose Lecanorae (L. crassa and 

L. saxicoUi) the lowest hyphae are somewhat more closely interwoven; 

they become brown in colour, and the lichen is attached to the substratum 

by rhizoid-like branches. In Lecanora lentigera there is a layer of parallel 

is reached when 

hyphae along the under surface. Further development 

a plectenchyma of thick-walled cells is formed both above and below, as in 

Psoroma hypnorum, though on the under surface the continuity is often 

broken. The squamules of Cladoniae are described under the radiate-stratose 

series. 

1 See p. 83. 

- Friedrich 1906. 

3 See p. 76.

82 

3. 

MORPHOLOGY 

FOLIOSE LICHENS 

A. DEVELOPMENT OF FOLIOSE THALLUS 

The larger leafy lichens are occasionally monophyllous and attached at 

a central point as in Umbilicaria, but mostly they are broken up into lobes 

which are either imbricate and crowded, or represent the dividing and 

branching of the expanding thallus at the circumference. They are horizontal 

spreading structures, with marginal and apical growth. The several 

tissues of the squamule are repeated in the foliose thallus, but further provision 

is made to meet the requirements of the larger organism. There is the 

greater development of cortical tissue, especially on the lower surface, and 

the more abundant formation of rhizoidal organs to attach the large flat 

fronds to the support. There are also various adaptations to secure the aera- 

tion of the internal tissues 1 

. 

B. CORTICAL TISSUES 

Schwendener 2 was the first who, with the improved microscope, made 

a systematic study of the minute structure of lichens. He examined typical 

species in genera of widely different groups and described their anatomy in 

detail. The most variable and perhaps the most important of the tissues 

of lichens is the cortex, which is most fully developed in the larger thalli, and 

as the same type of cortical structures recurs in lichens widely different in 

affinity as well as in form, it seems well to group together here the ascertained 

facts about these covering layers. 

a. TYPES OF CORTICAL STRUCTURE. Zukal 3 and , more recently 

Hue 4 have made , independent studies in the comparative morphology of 

the thallus and have given particular attention to the different varieties 

of cortex. They each find that the variations come under a definite series 

of types. Zukal recognized five of these : 

1. Pseudoparenchymatous (plectenchyma): by frequent septation of 

regularly arranged hyphae and by coalescence a kind of continuous cellstructure 

is formed. 

2. Palisade cells: the outer elongate ends of the hyphae lie close 

together in a direction at right angles to the surface of the thallus and form 

a coherent row of parallel cells. 

3. 

Fibrous: the cortical hyphae lie in strands of fine filaments parallel 

with the surface of the thallus. 

4. Intricate: hyphae confusedly interwoven and becoming dark in 

colour form the lower cortex of some foliose lichens. 

1 See p. 126. 

2 Schwendener 1860, 1863 and 1868. 3 Zukal 1895, p. 1305. 

4 Hue 1906.

STRATOSE THALLUS 

These four types, Zukal finds, are practically without interstices in the 

:issue and form a perfect protection against excessive transpiration. He adds 

êt another form: 

5. A cortex formed of hyphae with dark-coloured swollen cells, 

,vhich is not a protection against transpiration. It occurs among lower crus- 

:aceous forms. 

Hue has summed up the different varieties under four types, but as he 

las omitted the "fibrous" cortex, we arrive again at five different kinds of 

:ortical formation, though they do not exactly correspond 

ukal. A definite name is given to each type: 

to those of 

i. Intricate : an intricate dense layer of gelatinous-walled hyphae, 

Dranching in all directions, but not coalescent (Fig. 44). This rather unusual 

:ype of cortex occurs in Sphaerophorus and Stereocanlon, both of which 

lave an upright rigid thallus (fruticose). 

f 

Fig. 44. Sphaerophorus coralloides Pers. Transverse 

section of cortex and gonidial layer 

near the growing point of a frond x 600. 

Fig. 45. Roccellafudformis'DC. Transverse 

section of cortex near the 

growing point of a frond x 600. 

2. Fastigiate : the hyphae bend outwards or upwards 

to form the 

:ortex. A primary filament can be distinguished with abundant branches, 

all tending in the same direction; anastomosis may take place between the 

hyphae. The end branches are densely packed, though there are occasional 

interstices (Fig. 45). Such a cortex occurs in Thamnolia\ in several genera 

af Roccellaceae Roccellographa^ Roccellina, Reinkella, Pentagenella, Combea, 

Schizopelte and Roccella and also in the crustaceous genus Dirina. The 

fastigiate cortex corresponds with Zukal's palisade cells. 

3. Decomposed: in this, the most frequent type of cortex, the hyphae 

that travel up from the gonidial layer become irregularly branched and 

frequently septate. The cell-walls of the terminal branches become swollen 

into a gelatinous mass, the transformation being brought about by a change 

62

84 

MORPHOLOGY 

in the molecular constituents of the cell-walls which permits the imbibitior 

and storage of water. The tissue, owing to the enormous increase of the 

wall, is so closely pressed together that the individua 

Fig. 46. Lecanora glaucoma 

va.r.corrugata'Ny\. Vertical 

section of cortex x 500 (after 

Hue). 

hyphae become indistinct; the cell-lumen finall} 

disappears altogether, or, at most, is only to be 

detected in section as a narrow disconnected dart 

streak. The decomposed cortex is characteristic 

of many lichens, crustaceous (Fig. 46) and squamu- 

lose, as well as of such highly developed genera as 

Usnea, Letharia, Ramalina, Cetraria, Evernia anc 

certain Parmeliae. 

Zukal took no note of the decomposed cortex 

but the omission is intentional and is due to his 

regarding the structure of the youngest stages of the 

thallus near the growing point as the most typical and as giving the besi 

indication as to the true arrangement of hyphae in the cortex. He thu5 

describes palisade tissue as the characteristic cortex of Evernia, since the 

formation near the growing point of the fronds is somewhat palisade-like 

and he finds fibrous cortex at the tips of Usnea filaments. In both these 

instances Hue has described the cortex as decomposed because he takes 

account only of the fully formed thallus in which the tissues have reached 

a permanent condition. 

4. Plectenchymatous: the last of Hue's types corresponds with the 

first described by Zukal.Ît is the result of the lateral coherence and frequent 

septation of the hyphae into short almost square or rounded cells (Fig. 47) 

The simplest type of such a cortex can be studied in Leptogiumt a genus oi 

Fig. 47. Peltigera canina DC. Vertical section 

of cortex and gonidial zone x 600.


gelatinous lichens in which the tips of the hyphae are cut off at the surface 

by one or more septa. The resulting cells are wider than the hyphae and 

they cohere together to form, in some species, disconnected patches of cells; 

in others, a continuous cortical covering one or more cells thick, while in 

the margin of the apothecium they form a deep cellular layer. The cellular 

type of cortex is found also, as already stated, in some crustaceous Pertu- 

sariae, and in a few squamulose genera or species. It forms the uppermost 

layer of the Peltigera thallus and both cortices of many of the larger foliose 

lichens such as Sticta, Parmelia, etc. 

5. The "fibrous" cortex must be added to this series, as was pointed 

out by Heber Howe 1 who gave the less appropriate designation of "simple" 

to the type. It consists of long rather sparingly branched slender hyphae 

that grow in a direction parallel with the surface of the thallus (Fig. 48). 

It is characteristic of several fruticose and foliose lichens with more or less 

upright growth, such as we find in several of the Physciae, and in the allied 

genus TeloschisteS) in Alectoria, several genera of Roccellaceae, in Usnea 

longissima and in Parmelia pubescens, etc. Zukal would have included all 

the Usneae as the tips are fibrous. 

Fig. 48. Physcia ciliaris DC. Vertical section of thallus. a, cortex; 

b, gonidial zone; c, medulla, x 100. 

More than one type of cortex, as already stated, may appear in a genus; 

a striking instance of variability occurs in Solorina where, as Hue 2 has 

pointed out, the cortex of .S". octospora is fastigiate, that of all the other 

species being plectenchymatous. Cortical development is a specific rather 

than a generic characteristic. 

b. ORIGIN OF VARIATION IN CORTICAL STRUCTURE. The immediate 

causes making for differentiation in cortical development are: the prevailing 

direction of growth of the hyphae as they rise from the gonidial zone; the 

amount of branching and the crowding of the filaments ; 

septation ; 

the frequency of 

and the thickening or degeneration of the cell-walls which may 

1 Heber Howe 1912. Hue 1911.

86 

MORPHOLOGY 

become almost or entirely mucilaginous. In the plectenchymatous cortex, 

the walls may remain quite thin and the cells small as in Xanthoria parietina, 

or the walls may be much thickened as in both cortices of Sticta. 

As a result of stretching the cell may increase enormously in size: in some 

instances where the internal hyphae are about 3 ft to 4 /A in width, the 

cortical cells formed from these hyphae may have a cell cavity 15 /j, to 16/1, 

in diameter. 

c. Loss AND RENEWAL OF CORTEX. Very frequently 

the cortex is 

covered over by a layer of homogeneous mucilage which forms an outer 

cuticle. It arises from the continual degeneration of the outer cell-walls 

as was 

and it is liable to friction and removal by atmospheric agency 

first described by Schwendener 1 in the weather-beaten cortex of Umbi- 

licaria pustulata. He had noted the irregular jagged outline of the cross 

section of the thallus, and he then suggested, as the probable reason, the 

decay of the outer rind with the constant renewal of it by the hyphae from 

the underlying gonidial zone, though he was unable definitely to prove his 

theory. The peeling of the dead outer layer (with its replacement by new 

tissue) has however been observed many times since his day. It has been 

described by Darbishire 2 in Pertusaria: in that genus there is at first a 

primary cortex formed of hyphae that grow in a radial direction, parallel 

to the surface of the thallus. The walls of these hyphae become gradually 

more and jmore mucilaginous 

till the cells are obliterated. Meanwhile 

short-celled filaments grow up in serried ranks from the gonidial layer and 

finally push 

off the dead "fibrous" cortex. The new tissue takes on a 

plectenchymatous character, and the outer cells in time become decomposed 

and provide a mucilaginous cuticle which in turn is also subject to wasting. 

The same process of peeling was noted by Rosendahl 3 in some species of 

brown Parmeliae, where the dead tissues were thrown off in shreds, though 

only in isolated patches. But whether in patches or as a continuous sheath, 

there is constant degeneration, with continual renewal of the dead material 

from the internal tissues. 

The cortex is the most highly developed of all the lichen structures and 

from the various 

is of immense importance to the plant as may be judged 

adaptations to different needs 4 . The cortical cell-walls are frequently 

impregnated with some dark-coloured substance which, in exposed situa- 

tions, must counteract the influence of too direct sunlight and be of 

service in sheltering the gonidia. Lichen acids sometimes very brightly 

coloured and oxalic acid are deposited in the cortical tissues in great 

abundance and aid in retaining moisture; but the two chief functions to 


a Darbishire 1897. 

4 See p. 96. 

* Rosendahl 1907.


which the cortex is specially adapted are the checking of transpiration and 

the strengthening of the thallus against external strains. 

d. CORTICAL HAIRS OR TRICHOMES. Though somewhat rare, cortical 

hairs are present on the upper surface of several foliose lichens. They take 

rise, in all the instances noted, as a prolongation of one of the cell-rows 

forming a plectenchymatous cortex. 

In Peltidea (Peltigerd) apJithosa they are especially evident near the 

growing edges of the thallus; and they take part in the development of 

the superficial cephalodia 1 which are a constant feature of the lichen. They 

tend to disappear with age and leave the central older parts of the thallus 

smooth and shining. In several other species of Peltigera (P. canina, etc.) 

the life of the cortex. In these lichens 

they are present and persist during 

the cells of the cortical tissue are thin-walled, all except the outer layer, 

the membranes of which are much thicker. The hairs rising from them are 

also thick-walled and septate. Generally they branch in all directions and 

anastomose with neighbouring hairs so that a confused felted tangle is 

formed; they vary in size but are, as a rule, about double the width of the 

medullary hyphae as are the cortical cells from which they rise. They disappear 

from the thallus, frequently in patches, probably by weathering, but 

over large surfaces, and especially where any inequality affords a shelter, 

they persist as a soft down. 

Hairs are also present on the upper surface of some Parmeliae. Rosen- 

dahl 2 has described and figured them in P. glabra and P. verniculifera 

short pointed unbranched hyphae, two or more septate and with thickened 

walls. They are most easily seen near the edge of the thallus, though they 

persist more or less over the surface; they also grow on the margins of the 

apothecia. In P. verruculifera they arise from the soredia; in P. glabra 

a few isolated hairs are present on the under surface. 

formation of hairs on the 

In Nephromium tomentosum there is a scanty 

upper surface. They are abundant on the lower surface, and function as 

attaching organs. A thick tomentum of hairs is similarly present on the 

lower surface of many of the Stictaceae either as an almost unbroken 

covering or in scattered patches. In several species of Leptoginm they grow 

out from the lower cortical cells and attach the thin horizontal fronds ; 

very occasionally they are present in Collema. 

C. GONIDIAL TISSUES 

With the exception of some species of Collema and Leptogium lichens 

included under the term foliose, are heteromerous in structure, and the algae 

that form the gonidial zone are situated below the upper cortex and, there- 

1 See p. 133. 

2 Rosendahl 1907. 

and

88 

MORPHOLOGY 

fore, in the most favourable position for photosynthesis. Whether belonging 

to the Myxophyceae or the Chlorophyceae, they form a green band, straight 

and continuous in some forms, in others somewhat broken up into groups. 

In certain species they push up at intervals among the cortical cells, as in 

Gyropkora and in Parmelia tristis. In Solorina crocea a regular series of 

gonidial pyramids rises towards the upper surface. The green cells are 

frequently more dense at some points than at others, and they may penetrate 

in groups well into the medulla. 

The fungal tissue of the gonidial zone is composed of hyphae which 

have thinner walls, and are generally somewhat loosely interlacing. In 

Peltigera^ the gonidial hyphae are so connected by frequent branching and 

by anastomosis that a net-like structure is formed, in the meshes of which 

the algae a species of Nostoc are massed more or less in groups. In 

lichens with a plectenchymatous cortex, the cellular tissue may extend 

downwards into the gonidial zone and the gonidia thus become enmeshed 

among the cells, a type of formation well seen in the squamulose species, 

Dermatocarpon lachneum and Heppia Guepini, where the massive plectenchyma 

of both the upper and lower cortices encroaches on the pith. In 

Endocarpon and in Psoroma the gonidia are also surrounded by short cells. 

A similar type of structure occurs in Cora Pavonia, one of the Hymenolichenes: 

the gonidial hyphae in that species form a cellular tissue in which 

are embedded the blue-green Chroococcus cells 2 . 

D. MEDULLA AND LOWER CORTEX 

a. MEDULLA. The hyphal tissue of the dorsiventral thallus that lies 

between the gonidial zone and the lower cortex or base of the plant is 

always referred to as the medulla or pith. It is, as a rule, by far the most 

considerable portion of the thallus. In Parmelia caperata (Fig. 49), for 

instance, the lobes of which are about 300 /it thick, over 200 p of the space 

is occupied by this layer. It varies however very largely in extent in 

different lichens according to species, and also according to the substratttm. 

In another Parmelia with a very thin thallus, P. alpicola growing on quartzite, 

the medulla measures scarcely twice the width of the gonidial zone. 

It forms a fairly massive tissue in some of the crustaceous lichens in some 

Pertusariae and Lecanorae attaining a width of about 600 /*. 

Nylander 3 

distinguished three types of medullary tissue in lichens: 

(1) felted, which includes all those of a purely filamentous structure; 

(2) cretaceous or tartareous, more compact than the felted, and containing 

granular or crystalline substances as in some Pertusariae; and lastly 

(3) the cellular medulla in which the closely packed hyphae are divided 

1 Mey er '9 2 - 2 See p. 52. 

3 

Nyland e r l8s8 .


into short cells and a kind of plectenchyma is formed, 

(Psoromd) hypnorum, in Endocarpon, etc. 

Fig. 49. Parmelia caperala Ach. (S. H., Photo.}. 

as in Lecanora 

The felted medulla is characteristic of most lichens and is formed of 

loose slender branching septate hyphae with thickish walls. This interwoven 

hyphal texture provides abundant air-spaces. 

1 Hue has noted that the walls of the medullary hyphae in Parmeliae are 

smooth, unless they have been exposed to great extremes of heat or cold, 

when they become wrinkled or scaly. They are very thick-walled in Pelti- 

gera (Fig. 50). 

Fig. 50. Hyphae .from lower medulla of Peltigera canina DC. x 600. 

1 Hue 1898.

MORPHOLOGY 

b. LOWER CORTEX. In some foliose lichens such as Peltigera there is 

no special tissue developed on the under surface. In Lobaria pulmonaria 

large patches of the under surface are bare, and the medulla is exposed to 

the outer atmosphere, sheltered only by its position. In some other lichens 

the lowermost hyphae lie closer together and a kind of felt of almost parallel 

filaments is formed, generally darker in colour, as in Lecanora lentigera, and 

in some species of Physcia. 

Most frequently however the tissues of the upper cortex are repeated on 

the lower surface, though differing somewhat in detail. In all of the brown 

Parmeliae, according 

to Rosendahl 1 

, the structure is identical for both 

cortices, though the upper develops now hairs, now isidia, breathing pores, 

etc., while the lower produces rhizinae. The amorphous mucilaginous cuticle 

so often present on the upper surface is absent from the lower, the walls 

of the latter being often charged instead with dark-brown pigments. 

c. HYPOTHALLIC STRUCTURES. An unusual development of hyphae 

from the lower cortex occurs i-n the genera Anzia and Pannoparmelia both 

Fig. 51. Pannoparmelia anzioides Darb. 

Vertical section of thallus and hypo- 

thallus. 0, cortex ; b, gonidial zone ; 

i, medulla; d, lower cortex; e, hypothallus. 

x ca. 450 (after Darbishire). 

Rosendahl 1907. 

closely related to Parmelia whereby a 

loose sponge-like hypothallus of anasto- 

mosing 

one of the simpler types, Anzia colpodes, 

reticulate strands is formed. In 

a North American species, the hyphae 

passing out from the lower medulla become 

abruptly dark-brown in colour, and 

are divided into short thick-walled cells. 

Frequent branching and anastomosis of 

these hyphae result in the formation of 

a cushion-like structure about twice the 

bulk of the thallus. In another species 

from Australia (A. Japonica) there is a 

lower cortex, distinct from the medulla, 

consisting of septate colourless hyphae 

with thick walls. From these branch out 

free fi laments, similar in structure but dark 

in colour, which branch and anastomose 

as in the previous species. 

In Pannoparmelia the lower cortex 

and the outgrowths from it are several 

cells thick; they may be thick-walled as 

in Anzia, or they may be thin-walled as 

described and figured by Darbishire 2 in 

2 Darbishire 1912.


P annoparmelia anzioides, a species from Tierra del Fuego (Fig. 51). A somewhat 

dense interwoven felt of hyphae occurs also in certain parts of the 

under surface of Parmelia physodes*. 

This peculiar structure, regarded as a hypothallus, is probably of service 

in the retention of moisture. The thick cell-walls in most of the forms 

suggest some such function. 

E. STRUCTURES FOR PROTECTION AND ATTACHMENT 

Such structures are almost wholly confined to the larger foliose and 

fruticose lichens and are all of the same simple type ; they are fungal 

in origin and very rarely are gonidia associated with them. 

a. CILIA. In a few widely separated lichens stoutish cilia are borne, 

mostly on the margins of the thallus lobes, or on the margins of the apo- 

Fig. 52. Usneaflorida Web. Ciliate apothecia (S. H., Pkoto.). 

thecia (Fig. 52). They arise from the cortical cells or hyphae, several of 

which grow out in a compact strand which tapers gradually to a point. 

Cilia vary in length up to about I cm. or even longer. In some lichens they 

1 Porter 1919.

9 2 

MORPHOLOGY 

retain the colour of the cortex and are greyish or whitish-grey, as in Physcia 

ciliaris or in Physcia hispida (Fig. 1 10). They provide a yellow fringe to 

the apothecia of Physcia chrysophthalma and a green fringe to those of 

Usnea fiorida. They are dark-brown or almost black in Parmelia perlata 

var. ciliata and in P. cetrata, etc. as also in Gyrophora cylindrica. The fronds 

of Cetraria islandica and other species of the genus are bordered with short 

spinulose brown hairs whose main function seems to be the bearing of 

"pycnidia" though in many cases they are barren (Fig. 128). 

Superficial cilia are more rarely formed than marginal ones, but they are 

characteristic of one not uncommon British species, Parmelia proboscidea 

(P. pilosella Hue). Scattered over the surface of that lichen are numerous 

crowded groups of isidia which, frequently, are prolonged upwards as darkbrown 

or blackish cilia. Nearly every isidium bears a small brown spot on 

the apex at an early stage of growth. Similar cilia are sparsely scattered 

over the thallus, but their base is always a rather stouter grey structure, 

which suggests an isidial origin. Cilia also occur on the margin of the lobes. 

As lichens are a favourite food of snails, insects, etc., it is considered 

that these structures are protective in function, and that they impede, if 

they do not entirely prevent, the larger marauders in their work of destruction. 

b. RHIZINAE. Lichen rootlets are mainly for the purpose of attachment 

and have little significance as organs of absorption. They have been noted 

in only one crustaceous lichen, Varicellaria microsticta 1 an , alpine species 

that spreads over bark or soil, and which is further distinguished by being 

Fig. 53. Rhizoid of Parmelia exasferata Carroll (P. aspidota Rosend.). A, hyphae growing out 

from lower cortex x 450. B, tip of rhizoid with gelatinous sheath x 335 (after Rosendahl). 

provided with a lower cortex of plectenchyma. In foliose lichens they are 

frequently abundant, though by no means universal, and attach the spreading 

fronds to the support. They originate, as Schwendener 2 

pointed out, from 

the outer cortical cells, exactly as do the cilia, and are scattered over the 


2 Schwendener 1860.


under surface or are confined to special areas. Rosendahl 1 has described 

their development in the brown species of Parmeliae: the under cortex in 

these lichens is formed of a cellular plectenchyma with thickish walls ; the 

rootlets arise by the outgrowth of several neighbouring cells from some slight 

elevation near the edge of the thallus. Branching and interlacing of these 

growing rhizinal hyphae follow, the outermost frequently spreading outwards 

at right angles to the axis, and forming a cellular cortex. The apex of the 

rhizoid is generally an enlarged tuft of loose hyphae involved in mucilage 

(Fig- 53), a provision for securing firmer cohesion to the support; or the 

tips spread out as a kind of sucker. Not unfrequently neighbouring "rootlets" 

are connected by mucilage at the tips, or by outgrowths of their hyphae, 

and a rather large hold-fast sheath is formed. 

In species of Peltigera (Fig. 54) the rhizinae are confined to the veins 

or ridges (Fig. 55); they are thickish at the base, and are generally rather 

Fig. 54. Peltigera canina DC. (S. H., Photo ). 

r 

ig- 55- 

Under surface with veins and 

rhizoids (after Reinke). 

long and straggling. Meyer 2 states that the central hyphae are stoutish 

and much entangled owing to the branching and frequent anastomosis of 

one hypha with another; the peripheral terminal branches are thinner-walled 

and free. These rhizinae vary in colour from white in Peltigera canina to 

brown or black in other species. Most species of Peltigera spread over grass 

or mosses, to which they cling by these long loose "rootlets." 

Lichen rhizinae, distinguished by Reinke 3 as "aerial rhizinae," are more 


2 Meyer 1902. 

3 Reinke 1895, p. 186.

94 

MORPHOLOGY 

or less characteristic of all the species of Parmelia with the exception of 

those belonging to the subgenus Hypogymnia in which they are of very rare 

occurrence, arising, according 

1 

to Bitter , only in response to some external 

friction. They are invariably dark-coloured, rather short, about one to a 

few millimetres in length, and are simple or branched. The branches may 

go off at any angle and are sometimes curved back at the ends in anchorlike 

fashion. The Parmeliae grow on firm substances, trees, rocks, etc., and 

the irregularities of their attaching structures are conditioned by the obstacles 

encountered on the substratum. Not unfrequently the lobes are attached 

by the rhizinae to underlying portions of the thallus. 

In the genus Gyrophora, the rhizinae are simple strands of hyphae 

(G. polyrhizd) or they are corticate structures (G. murina, G. spodochroa 

and G. vellea\ They are also present in species of Solorina, Ricasolia, 

Sticta and Physcia and very sparingly in Cetraria (Platysma). 

c. HAPTERA. Sernander 2 has grouped all the more distinctively aerial 

organs of attachment, apart from rhizinae, under the term "hapteron" and he 

has described a number of instances in which cilia and even the growing 

points of the thallus may become transformed to haptera or sucker-like 

sheaths. 

The long cilia of Physcia ciliaris occasionally form haptera at their tips 

where the hyphae are loose and in active growing condition. Contact with 

some substance induces branching by which a spreading sheath arises; a 

plug-like process may also be developed which pierces the substance encountered 

not unfrequently another lobe of its own thallus. The long 

flaccid fronds of Evernia furfuracea are frequently connected together by 

bridge-like haptera which rise at any angle of the thallus or from any part 

of the surface. 

The spinous hairs that border the thalline margins in Cetraria may also, 

in contact with some body often another frond of the lichen form a 

hapteron, either while the spermogonium, which occupies the tip of the 

spine, is still in a rudimentary stage, or after it has discharged its spermatia. 

The small sucker sheath may in that case arise either from the apex of the 

cilium, from the wall of the spermogonium or from its base. By means of 

these haptera, not only different individuals become united together, but 

instances are given by Sernander in which Cetraria islandica, normally a 

ground lichen, had become epiphytic by attaching itself in 

trunk of a tree (Pinus sylvestris}. 

this way to the 

In Alectoria, haptera are formed at the tip of the thallus filament as an 

apical cone-like growth from which hyphae may branch out and penetrate 

any convenient object. A species of this genus was thus found clinging to 


2 Sernander 1901.


stems of Betula nana. Apical haptera are very frequent in Cladonia rangiferina 

and Cl. sylvatica, induced here also by contact. These two plants, as 

well as several species of Cetraria, tend, indeed, to become entirely epiphytic 

on the heaths of the Calluna formations. Haptera similar to those of Alectoria 

occur in Usnea, Evernia, Ramalina and Cornicularia (Cetraria). In Evernia 

prunastri var. stictoceros, a heath form, the fronds become attached to the 

stems and branches of Erica tetralix by hapteroid strands of slender glutinous 

hyphae which persist on the frond of the lichen after it is detached as 

small very dark tubercles surmounted, as Parfitt 1 

pointed out, by a darkbrown 

grumous mass of cells. Plug-like haptera may be formed at the base 

of Cladoniae which attach them to each other and to the substratum. The 

brightly coloured fronds of Letharia vulpina are attached to each other in 

somewhat tangled fashion by lateral bridges or by fascicles of hyphae darkbrown 

at the base but colourless at the apices, exactly like aerial adventitious 

rhizinae. They grow out from the fronds generally at or near the tips and 

lay hold of a neighbouring frond by means of mucilage. These haptera are 

evidently formed in response to friction. Haptera along with other lichen 

2 

attachments have received considerable attention from . Gallic He finds 

them arising on various positions of the lichen fronds and has classified 

them accordingly. 

After the haptera have become attached, they increase in size and strength 

and supply a strong anchorage for the plant; the point of contact frequently 

forms a basis for renewed growth while the part beneath the hapteron may 

characteristic of fruticose 

gradually die off. Haptera are more especially 

lichens, but Sernander considers that the rhizinae of foliose species may 

function as haptera. They are important organs of tundra and heath 

formations as they enable the lichens to get a foothold in well-lighted 

positions, and by their aid the fronds are more able to resist the extreme 

tearing strains to which they are subjected in lands. 

high and unsheltered moor- 

F. STRENGTHENING TISSUES OF STRATOSE LICHENS 

Squamulose and foliose lichens grow mostly in close relation with the 

support, and the flat expanding thallus, as in the Parmeliae, is attached at 

many points to the substance tree, rock, etc. over which the plants spread. 

and the lobes remain 

Special provision for support is therefore not required, 

thin and flaccid. Yet, in a number of widely different genera the attachment 

to the substratum is very slight, and in these we find an adaptation of 

existing tissues fitted to resist tearing strains, resistance being almost 

invariably secured by the strengthening of the cortical layers. 

1 Parfitt in Leighton 1871, p. 470. 

2 Gallic 1915.

96 

MORPHOLOGY 

a. BY DEVELOPMENT OF THE CORTEX. Such a transformation of tissue 

is well illustrated in Heppia Guepini. The thallus consists of rigid squamules 

which are attached at one point only ; the cortex of both surfaces is plecten- 

chymatous and very thick and even the medulla is largely cellular. 

The much larger but equally rigid coriaceous thallus of Dermatocarpon 

miniatum (Fig. 56) has also a single central attachment or umbilicus, and 

Fig- 56. Dermatocarpon miniatum Th. Fr. (S. H., Photo.). 

both cortices consist of a compact many-layered plectenchyma. The same 

structure occurs in Umbilicaria pitstnlata and in some species of Gyrophora, 

which, having only a single central hold-fast, gain the necessary stiffening 

through the increase of the cortical layers. 

In the Stictaceae there are a large number of widely-expanded forms, 

and as the attachment depends mostly on a somewhat short tomentum, 

strength is obtained here also by the thick plectenchymatous cortex of both 

surfaces. When areas denuded of tomentum and cortex occur, as in Lobaria 

pulmonaria, the under surface is not sensibly weakened, since the cortical 

tissue remains connected in a stout and firm reticulation. 

b. BY DEVELOPMENT OF VEINS OR NERVES. Certain ground lichens 

belonging to the Peltigeraceae have a wide spreading thallus often with 

very large lobes. The upper cortex is a many-layered plectenchyma, but 

the under surface is covered only by a loose felt of hyphae which branch 

out into a more or less dense tomentum. As the firm upper cortex continues 

to increase by intercalary growth from the branching upwards of hyphae 

from the meristematic gonidial zone, there occurs an extension of the upper


thallus 

1 

with which the lower cannot . keep pace A little way back from 

the edge, the result of the stretching is seen in the splitting asunder of the 

felted hyphae of the under surface, and in the consequent formation of a 

reticulate series of ridges known as the veins or nerves ; they represent the 

original tomentose covering, and are white, black or brown, according to the 

colour of the tomentum itself. The naked ellipsoid interstices show the 

white medulla, and, if the veins are wide, the colourless areas are correspond- 

ingly small. Rhizinae are formed on the nerves in several of the species, 

and anchor the thallus to the support. In Peltigera canina, the under surface 

is almost wholly colourless, the veins are very prominent (Fig. 55), and are 

further strengthened by the growth and branching of the parallel hyphae of 

which they are composed. They serve to strengthen the large and flabby 

thallus and form a rigid base for the long rhizinae by which the lichen clings 

to the grass or moss over which it grows. 

The most perfect development of strengthening nerves is to be found in 

HydrotJiyria venosa*, a rather rare water lichen that occurs in the streams of 

North America. It consists of fan-like lobes of thin structure, the cortex 

being only about one cell thick. The fronds are about 3 cm. wide and they 

are contracted below into a stalk which serves to attach the plant to the 

substratum. Several fronds may grow together in a dense tuft, the expanded 

upper portion floating freely in the water. Frequently the plants form a 

dense growth over the rocky beds of the stream. 

At the point where the stalk expands into the free erect frond, there 

arise a series of stout veins which spread upwards and outwards. They are 

tissues : 

definitely formed structures and not adaptations of pre-existing 

certain hyphae arise from the medulla at the contracted base of the frond, 

take a radial direction and, by increase, become developed into firm strands. 

The individual hyphae also increase in size, and the swelling of the nerve 

gives rise to a ridge prominent on both surfaces. They seldom anastomose 

at first but towards the tips they become smaller and spread out in delicate 

ramifications which unite at various points. There is no doubt, as Bitter 1 

points out, that the nerves function as strengthening tissues and preserve the 

frond from the strain of the water currents which would, otherwise, tear apart 

the delicate texture. 


2 

Sturgis 1890. 

7-

9 8 

MORPHOLOGY 

III. RADIATE THALLUS 

i. CHARACTERS OF RADIATE THALLUS 

In the stratose dorsiventral thallus, there is a widely extended growing 

area situated round the free margins of the thallus. In the radiate thallus 

of the fruticose or filamentous lichens, growth is confined to an apical region. 

Attachment to the substratum is at one point only the base of the plant 

thus securing the exposure of all sides equally to light. The cortex 

surrounds the fronds, and the gonidia (mostly Protococcaceae) lie in a zone 

or in groups between the cortex and the medulla. It is the highest type of 

since it secures the widest 

vegetative development in the lichen kingdom, 

room for the gonidial layer, and the largest opportunity for photosynthesis. 

Shrubby upright lichens consist mostly of strap-shaped fronds, either 

simple or branched, which may be broadened to thin bands (Fig. 57) or 

may be narrowed and thickened till they are almost cylindrical. The fronds 

vary in length according to the species from a few millimetres upwards: 

Fig. 57. Roccellafuciformis DC.

RADIATE THALLUS 99 

those of Roccella have been found measuring 30 cm. in length ; those of 

Ramalina reticulata, the largest of all the American lichens, extend to con- 

siderably more. 

Lichens of filamentous growth are more or less cylindrical (Fig. 58). 

They are in some species upright and of moderate length^ 

but in a few 

Fig. 58. Usnea barbata Web. (S. H., Photo.}, 

pendulous forms they grow to a great length : specimens of Usnea longissima 

have been recorded that measured 6 to 8 metres from base to tip. 

The radiate type of thallus occurs in most of the lichen groups but most 

frequently in the Gymnocarpeae. In gelatinous Discolichens it is represented 

in the Lichinaceae. It is rare : among Pyrenocarpeae there is one 

very minute British lichen in that series, Pyrenidium actinellum, and one 

from N. America, Pyrenothamnia, that are of fruticose habit. 

2. INTERMEDIATE TYPES OF THALLUS 

Between the foliose and the fruticose types, there are intermediate forms 

that might be, and often are, classified now in one group and now in the 

other. These are chiefly : Physcia (Anaptychia) dliaris, Ph. leucomelas and 

the species of Evernia. 

72

100 

MORPHOLOGY 

In the two former the habit is more or less fruticose as the plants are 

affixed to the substratum at a basal point, but the fronds are decumbent and 

the internal structure is of the dorsi ventral type : there is an upper "fibrous" 

cortex of closely compacted parallel hyphae, a gonidial zone the gonidia 

lying partly in the cortex and partly among the loose hyphae of the 

medulla and a lower cortex formed of a weft of hyphae which also run 

somewhat parallel to the surface. Both species are distinguished by the 

numerous marginal cilia, either pale or dark in colour. These two lichens 

are greyish-coloured on the upper surface and greyish or whitish below. 

1 

Everniafurfuracea with a basal attachment and with a , partly horizontal 

and partly upright growth, has a dorsiventral thallus, dark greyish-green 

above and black beneath, with occasional rhizinae towards the base. The 

cortex of both surfaces belongs to the "decomposed" type; the gonidial 

zone lies below the upper surface, and the medullary tissue is of loose hyphae. 

In certain forms of the species isidia are abundant on the upper surface, 

a character of foliose rather than of fruticose lichens. E. furfuracea grows 

on trees and very frequently on palings. 

Fig. 5Q. Evernia prunastri Ach. (M. P., Photo.}. 

1 See p. 108.


E. prunastri, the second species of the genus, is more distinctly upright in 

habit, with a penetrating basal hold-fast and upright strap-shaped branching 

fronds, light-greyish green on the "upper" surface and white on the other 

(Fig. 59). The internal structure is sub-radiate; both cortices are "decom- 

posed"; the gonidial zone consists of somewhat loose groups of algae, very 

constant below the "upper" surface, with an occasional group in the pith 

near to the lower cortex in positions that are more exposed to light. There 

is also a tendency for the gonidial zone to pass round the margin and spread 

some way along the under side. The medulla is of loose arachnoid texture 

and the whole plant is very limp when moist. It grows on trees, often in 

dense clusters. 

3. 

FRUTICOSE AND FILAMENTOUS THALLUS 

A. GENERAL STRUCTURE OF THALLUS 

The conditions of strain and tension in the upright plant are entirely 

different from those in the decumbent thallus, and to meet the new require- 

ments, new adaptations of structure are provided either in the cortex or in 

the medulla. 

CORTICAL STRUCTURES. With the exception of the distinctly plectenchymatous 

cortex, all the other types already described recur in fruticose 

lichens; in various ways they have been modified to provide not only covering 

but support to the fronds. 

a. The fastigiate cortex. This reaches its highest development in 

Roccella in which the branched hyphal tips, slightly clavate and thick-walled, 

lie closely packed in palisade formation at right angles to the main axis 

(Fig. 45). They afford not only bending power, but give great consistency 

to the fronds. The cortex is further strengthened in R. fuciformis* by the 

compact arrangement of the medullary hyphae that run parallel with the 

surface, and among which occur single thick-walled filaments. The plant 

and the narrow strap- 

grows on maritime rocks in very exposed situations ; 

shaped fronds, as stated above, may attain a length of 30 cm., though usually 

they are from 10 to i8cm. in height. The same type of cortex, but less 

highly differentiated, affords a certain amount of stiffness to the cylindrical 

much weaker fronds of Thamnolia. 

b. The fibrous cortex. This type is found in a number of lichens with 

long filamentous hanging fronds. It consists of parallel hyphae, rarely septate 

and rarely branched, but frequently anastomosing and with strongly thick- 

ened "sclerotic" walls. Such a cortex is the only strengthening element in 

Alectoria, and it affords great toughness and flexibility tc .the thong-like 

1 Darbishire 1808.

102 

MORPHOLOGY 

thallus. It is also present in Ramalina (Alectoria) thrausta, a species with 

slender fronds (Fig. 60). 

Fig. 60. Alectoria thrausta Ach. A, transverse section of frond; 

a, cortex; b, gonidia; c, arachnoid medulla x 37. B, fibrous 

hyphae from longitudinal section of cortex, x 430 (after Brandt). 

In Usnea longissima the cortex both of the fibrillose branchlets and of 

the main axis is fibrous, and is composed of narrow thick-walled hyphae 

which grow in a long spiral round 

II 

'!!' 

vi 

it 

Usnea longissima Ach. Longitudinal 

sections of outer cortex. A, near the apex; B, 

the middle portion of fibril, xjs^ (after 

Schulte). 

the central strand. The hyphae 

become more frequently septate 

further back from the apex (Fig. 6l). 

Such a type of cortex provides an 

exceedingly elastic and efficient protection 

for the long slender thallus. 

The same type of cortex forms 

the strengthening element in the 

fruticose or partly fruticose members 

of the family Physciaceae. One of 

\\\es>e.,Teloschistesflavicans, is a bright 

yellow filamentous lichen with a 

somewhat straggling habit. The 

fronds are very slender and are either 

cylindrical or slightly flattened. The


hyphae of the outer cortex are compactly fibrous; added toughness is 

given by the presence of some longitudinal strands of hyphae in the central 

pith. 

Another still more familiar grey lichen, Physcia ciliaris, has long flat 

branching fronds which, though dorsiventral in structure, are partly upright 

in habit. Strength is secured as in Teloschistes by the fibrous upper cortex. 

Other species of Physciae are somewhat similar in habit and in structure. 

In Dendrographa leucophaea, a slender strap-shaped rock lichen, Darbi- 

shire 1 has described the outer cortex as composed of closely compacted 

parallel hyphae resembling the strengthening cortex of Alectoria and very 

different from the fastigiate cortex of the Roccellae with which it is usually 

classified. 

B. SPECIAL STRENGTHENING STRUCTURES 

a. SCLEROTIC STRANDS. This form of strengthening tissue is charac- 

teristic of Ramalina. With the exception of R. thrausta (more truly an 

Alectoria} all the species have a rather weak cortical layer of branching 

intricate thick-walled hyphae, regarded by Brandt 2 as plectenchymatous, 

but more correctly by Hue 3 as "decomposed" on account of the gelatinous 

walls and diminishing lumen of the irregularly arranged cells. 

In R. evernioides, a plant with very wide flat almost decumbent fronds 

of soft texture, in R. ceruchis and in R. homalea there is a somewhat compact 

medulla which gives a slight stiffness to the thallus. The other species of 

the genus are provided with strengthening mechanical tissue within the 

cortex formed of closely united sclerotic hyphae that run parallel to the 

surface (Fig. 62). 

In a transverse section of the thallus, this tissue appears 

A B 

Fig. 62. Ramalina minuscula Nyl. A, transverse section 

of frond x 37; B, longitudinal strengthening hyphae of 

inner cortex x 430 (after Brandt). 


2 Brandt 1906. 

3 Hue 1906.

104 

MORPHOLOGY 

sometimes as a continuous ring which may project irregularly into the pith 

it is frequently in the form of strands or bundles which 

(R. calicaris) ; more 

alternate with the groups of gonidia (R. siliquosa, R. Curnozvii, etc.). In 

R. fraxinea these strands may be scarcely discernible in young fronds, though 

sometimes already well developed near the tips. Occasionally isolated strands 

of fibres appear in the pith (R. Curnowii\ or the sclerotic projections may 

even stretch across the pith to the other side (R. strepsilis} (Fig. 75 B). 

In the Cladoniae support along with flexibility is secured to the upright 

that form round the 

podetium by the parallel closely packed hyphae 

hollow cylinder a band called the "chondroid" layer from its cartilage-like 

consistency. 

b. CHONDROID AXIS. The central medullary tissue in Ramalina is, with 

few exceptions, a loose arachnoid structure ; often the fronds are almost 

hollow. In one species of Usnea, U. Taylori, found in polar regions, there 

is a similar loose though very circumscribed medullary and gonidial tissue 

in the centre of the somewhat cylindrical thallus, and a wide band of sclerotic 

fibres towards the cortex. 

Fig. 63 A. 

branch. 

longissi 

A, (Jinea barbata Web. Longitudinal section of filament with young adventitious 

, chondroid axis; /;, gonidial tissue; c, cortex, x too (after Schwendener). B, U. 


In Letharia (L. vulpina, etc.) the structure is midway between Ramalina 

and Usnea : the central axis is either a solid strand of chondroid hyphae or 

several separate strands. 

Fig. 63 B. Usnea lo ngissima Ach. A, transverse section of fibril x 85. B, a, chondroid axis; 

b, gonidial tissue; c, cortex x 525 (after Schulte). 

In three other genera with upright fruticose thalli, Sphaerophorus, Ar- 

gopsis and Stereocaulon, rigidity is maintained by a medulla approaching the 

chondroid type. In Sphaerophorus the species may have either flattened or 

cylindrical branching stalks, but in all of them, the centre is occupied by 

longitudinal strands of hyphae. Argopsis, a monotypic genus from Ker- 

guelen, has a cylindrical branching thallus with a strong solid axis; it is 

closely allied to Stereocaulon, a genus of familiar moorland lichens. The 

central tissue of the stalks in Stereocaulon is also composed of elongate, 

thick-walled conglutinate hyphae, formed into a strand which is, however, 

not entirely solid. 

C. SURVEY OF MECHANICAL TISSUES 

Mechanical tissues scarcely appear among fungi, except perhaps as 

stoutish cartilaginous hyphae in the stalks of some Agarics (Collybiae, etc.), 

or as a ring of more compact consistency round the central hyphae of 

rhizomorphic strands. It is practically a new adaptation of hyphal structure 

confined to lichens of the fruticose group, where there is the same requirement 

as in the higher plants for rigidity, flexure and tenacity. 

Rigidity is attained as in other plants by groups or strands of mechanical 

tissue situated close to the periphery, as they are so arranged in Rama- 

lina and Cladonia; or the same end is achieved by a strongly developed

io6 

MORPHOLOGY 

fastigiate cortex as in Roccella. Bending strains to which the same lichens 

are subjected, are equally well met by the peripheral disposition of the 

mechanical elements. 

Tenacity and elasticity are provided for in the pendulous forms either 

by a fibrous cortex as in Alectoria, or by the chondroid axis in Usnea. 

has recorded some interesting results of tests made by him as 

Haberlandt 1 

to the stretching capacity of a freshly gathered pendulous species in which 

the central strand was from -5 to I mm. thick. He found he could draw it 

out 100 to no per cent, of its normal length before it gave way. In an 

upright species the frond broke when stretched 60 to 70 per cent. In both 

of the plants tested, the central strand retained its elasticity up to 20 per 

cent, of stretching. The outer cortical tissue was cracked and broken in 

the experiments. Schulte 2 calculated somewhat roughly the tenacity of 

Usnea longissima and found that a piece of the main axis 8 cm. long carried 

up to 300 grms. without breaking. 

D. RETICULATE FRONDS 

In the upright radiate thallus, more especially among the Ramalinae, 

though also among Cladoniae\\h.&z has appeared a reticulate thallus resulting 

from the elongate splitting of the tissues, and due to unequal growth tension 

and straining of the gelatinous cortex when swollen with moisture. In 

several species of Ramalina, the strap-shaped frond is hollow in the centre ; 

and strands of strengthening fibres give rise to a series of cortical ridges. 

The thinner tissue between is frequently torn apart and ellipsoid openings 

appear which do not however pierce beyond the central hollow. Such breaks 

are irregular and accidental though occurring constantly in Ramalina 

fraxinea, R. dilacerata, etc. 

A more complete type of reticulation is always present in a Californian 

lichen, Ramalina reticulata, in which the large flat frond is a delicate open 

network from tip to base (Fig. 64). It grows on the branches of deciduous 

trees and hangs in crowded tufts up to 30 cm. or more in length. Usually 

it is so torn, that the real size attainable can only be guessed at. It is 

attached at the base by a spreading discoid hold-fast, and, in mature plants, 

consists of a stoutish main axis from which side branches are irregularly 

given off. These latter are firm at the base like the parent stalk, but soon 

they broaden out into very wide fronds. Splitting begins at the tips of the 

branches while still young ; they are then spathulate in form with a slightly 

narrower recurved tip, below which the first perforations are visible, small at 

first, but gradually enlarging with the growth of the frond. 

Ramalina reticulata is an extremely gelatinous lichen and the formation 

1 Haberlandt 1896. 

2 Schulte 1904. See p. 120.

I08 

MORPHOLOGY 

of the network was supposed by Lutz 1 to be entirely due to the swelling of 

the tissues, or the imbibition of water, causing tension and splitting. A more 

exact explanation of the phenomenon is given by Peirce 2 : he found that it 

was due to the thickened incurved tip, which, on the addition of moisture, 

swells in length, breadth and thickness, causing it to bend slightly upwards 

and then curve backwards over the thallus, thus straining the part immediately 

behind. These various movements result in the splitting of the frond 

while it is young and the cortices are thin and weak. 

Peirce made a series of experiments to test the capacity of the tissues 

to support tensile strains. In a dry state, a piece of the lichen held a weight 

up to I50grms.; when wet it broke with a weight of 3Ogrms. 

observed that the thickness of the frond doubled on wetting. 

It was also 

E. ROOTING BASE IN FRUTICOSE LICHENS 

Fruticose and filamentous lichens are distinguished by their mode of 

attachment to the substratum : instead of a system of rhizinae or of hairs 

spread over a large area, there is usually one definite rooting base by which 

the plant maintains its hold on the support. 

Intermediate between the foliose and fruticose types of thallus are 

several species which are decumbent in habit, but which are attached at one 

(or sometimes more) definite points, with but little penetration of the under- 

lying substance. One such lichen, Evernia furfuracea, has been classified 

now as foliose, and again as fruticose. The earliest stage of the thallus is 

in the form of a rosette-like sheath which bears rhizinae on the under 

surface, very numerous at the centre of the sheath, but entirely wanting 

towards the periphery. A secondary thallus of strap-shaped rather narrow 

fronds rises from the sheath and increases by irregular dichotomous branching. 

These branches, which are considered by Zopf 3 as adventitious, may 

also come into contact with the substratum and produce a few rhizinae at 

that point; or if the frond is more closely applied, the irritation thus 

produced causes a still greater outgrowth of rhizinae and the formation of 

a new base from which other fronds originate. These renewed centres of 

growth are not of very frequent occurrence; they were first observed and 

described by Lindau 4 in another species, Evernia prunastri, and were aptly 

compared by him to the creeping stolons of flowering plants. 

Evernia furfuracea grows frequently on dead wood, palings, etc., as well 

as on trees. E.prunastri grows invariably on trees, and has a more constantly 

upright fruticose' habit; in this species also, a basal sheath is present, and 

the attachment is secured by means of rhizoidal hyphae which penetrate 

deeply into the periderm of the tree, taking advantage of the openings 

1 Lutz 1894. 

2 Peirce 1898. Zop f 1903. 

* Lindau 1895.


afforded by the lenticels. The sheath hyphae are continuous with the medul- 

lary hyphae of the frond, and gonidia are frequently enclosed in the tissues ; 

the sheath spreads to some extent over the surface of the bark, and round 

the base of the fronds, thus rendering the attachment of the lichen to the 

tree doubly secure. 

Among Ramalinae, the development of the base was followed 1 

by Brandt 

in one species, R. Landroensis, an arboreal lichen from S. Tyrol. A rosette- 

like sheath was formed consisting solely of strands of thick-walled hyphae 

which spread over the bark. There were no gonidia included in the tissue. 

A different type of attachment was found by Lilian Porter 2 in corti- 

colous Ramalinae R. fraxinea, R. fastigiata, and R. pollinaria. The lichens 

were anchored to the tree by strands of closely compacted hyphae longitudinally 

arranged and continuous with the cortical hyphae. These enter 

the periderm of the tree by cracks or lenticels, and by wedge action cause 

extensive splitting. The strands may also spread horizontally and give rise 

to new plants. The living tissues of the tree were thus penetrated and 

injured, and there was evidence that hypertrophied tissue was formed and 

caused erosion of the wood. 

Several Ramalinae R. siliquosa, R. Curnowii, etc. grow on rocks, 

often in extremely exposed situations, in isolated tufts or in crowded swards 

(Fig. 65). The separate tufts are not unfrequently connected at the base by 

Fig. 6;. Ramalina siliquosa A. L. Sm., on rocks, reduced (M. P., Photo.). 


2 Porter 1916.

IIO 

MORPHOLOGY 

a crustaceous thallus. It is possible also to see on the rock, here and there, 

small areas of compact thalline granules that have scarcely begun to put out 

the upright fronds. These granules are corticate on the upper surface and 

contain gonidia; from the lower surface, slender branching hyphae in rhizoid- 

like strands penetrate down between the inequalities and separable particles 

of the rock, if the formation is granitic. They frequently have groups of 

gonidia associated with them, and they continue to ramify and spread, the 

pure white filaments often enough enclosing morsels of the rock. The 

upright fronds are continuous with the base and are thus securely anchored 

to the substratum. 

On a smooth rock surface such as quartzite a continuous sward o*f Rama- 

Una growth is impossible. The basal hyphae being unable to penetrate the 

even surface of the rock, the attachment is slight and the plants are easily 

dislodged. They do however succeed, sometimes, in taking hold, and small 

groups of fronds arise from a crustaceous base which varies in depth from 

5 to i mm. The tissues of this base are : very irregularly arranged towards 

the upper surface loose hyphae with scattered groups of algae are traversed 

by strands of gelatinized sclerotic hyphae similar to the strengthening tissues 

of the upright fronds, while down below there are to be found not only 

slender hyphae, but a layer of gonidia visible as a white and green film on 

the rock when the overlying particles are scaled off. 

Darbishire 1 found that attachment to the substratum by means of a 

basal sheath was characteristic of all the genera of Roccellaceae. He looks 

on this sheath, which is the first stage in the development of the plant, as 

a primary or proto-thallus, analogous to the primary squamules of the 

Cladoniae, and he carries the analogy still further by treating the upright 

fronds as podetia. The sheath of the Roccellaceae varies in size but it is 

always of very limited extent; it is mainly composed of medullary hyphae, 

and gonidia may or may not be present. The whole structure is permanent 

and important, and is generally protected by a well-developed upper cortex 

similar in structure to that of the upright' thallus, i.e. of a fastigiate type. 

There is no lower cortex. 

The two British species of Roccella R. fuciformis and R. phycopsis 

grow on maritime rocks, the latter also occasionally on trees. In R. fuci- 

formis, the attaching sheath is a flat structure which slopes up a little round 

the base of the upright frond. It is about 2 mm. thick, the cortex occupying 

about 40 /A of that space; a few scattered gonidia are present immediately 

below. The remaining tissue of the sheath is composed of firmly wefted 

slender filaments. Towards the lower surface, there is a more closely com- 

pacted dark brown layer from which pass out the hyphae that penetrate 

the rock. 

1 Darbishire 1898.

RADIATE THALLUS in 

The sheath of R. phycopsis is a small structure about 3 to 4 mm. in width 

and 1*5 mm. thick. A few gonidia may be found below the dense cortical 

layer, but they tend to disappear as the upright fronds become larger and 

the shade, in consequence, more dense. Lower down the hyphae take an 

intensely yellow hue; mixed with them are also some brown filaments. 

A somewhat larger sheath 7 to 8 mm. wide forms the base of R. tinctoria. 

In structure it corresponds as do those of the other species with the ones 

already described. 

In purely filamentous species such as Usnea there is also primary sheath 

formation : the medullary hyphae spread out in radiating strands which 

force their way wherever possible into the underlying substance; on trees 

they enter into any chink or crevice of the outer bark like wedges ; 

or they 

ramify between the cork cells which are split up by the mere growth pressure. 

By the vertical increase of the base, the fronds may be hoisted up and 

an intercalary basal portion may arise lacking both gonidia and cortical 

layer. Very frequently several bases are united and the lichen appears to 

be of tufted habit. 

A basal sheath provides a similar firm attachment for Alectoria jubata 

and allied species: these are slender mostly dark brown lichens which hang 

in tangled filaments from the branches of trees, rocks, etc. 

These attaching sheaths differ in function as well as in structure from 

the horizontal thallus of the Cladoniaceae. They may be more truly com- 

pared with the primary thallus of the red algae Dumontia and Phyllophora 

which are similarly affixed to the substratum, while upright fronds of 

subsequent formation bear the fructifications. 

IV. STRATOSE-RADIATE THALLUS 

i. STRATOSE OR PRIMARY THALLUS 

A. GENERAL CHARACTERISTICS 

This series includes the lichens of one family only, the Cladoniaceae, the 

genera of which are characterized by the twofold thallus, 

one portion being primary, horizontal and stratose, the 

other secondary and radiate, the latter an upright simple 

or branching structure termed a "podetium" which nar- 

rows above, or widens to form a trumpet-shaped cup or 

"scyphus" (Fig. 66). The apothecia are terminal on the 

pocletium or on the margins of the scyphi ; 

in a few species 

they are developed on the primary thallus. Some degree 

of primary thallus-formation has been demonstrated in all Fig. 

66. Cladonia 

, , r ., , pyxidata Hoffrn. 

the genera, if not in all the species of the family. The Basai sq uamule and 

êiius Cladina was established to include those species podetium. a, apothecia; 

s, spermoof 

Cladonia in which, it was believed, only a secondary gonia (after Krabbe).

ii2 

MORPHOLOGY 

podetial thallus was present, but Wainio 1 found in Cladonia sylvatica a 

granular basal crust and, in Cladonia uncialts, minute round scales with crenate 

margins measuring from -5 to I mm. in width. In some species (subgenus 

Cladina) the primary thallus is quickly evanescent, in others it is granular 

or squamulose and persistent. Where the basal thallus is so much reduced 

as to be practically non-existent, apothecia are rarely developed and soredia 

are absent Renewal of growth in these lichens is secured by the dispersal 

of fragments of the podetial thallus; they are torn off and scattered by the 

wind or by animals, and, if suitable conditions are met, a new plant arises. 

Cladonia squamules vary in size from very small scales as in Cl. uncialis 

to the fairly large foliose fronds of Cl.foliacea which extend to 5 cm. in length 

and about i cm. or more in width. It is interesting to note that when the 

primary thallus is well developed, the podetia are relatively unimportant 

and frequently are not formed. As a rule the squamules are rounded or 

somewhat elongate in form with entire or variously cut and crenate margins. 

They may be very insignificant and sparsely scattered over the substratum, 

or massed in crowded swards of leaflets which are frequently almost upright. 

In colour they are bluish-grey, yellowish or brownish above, and white 

beneath (red in Cl. miniata], frequently becoming very dark-coloured towards 

the rooting base. These several characteristics are specific and are often of 

considerable value in diagnosis. In certain conditions of shade or moisture, 

squamules are formed on the podetium 

basal squamules of the species. 

; they repeat the characters of the 

B. TISSUES OF THE PRIMARY. THALLUS 

The stratose layers of tissue in the squamules of Cladonia are arranged 

as in other horizontal thalli. 

a. CORTICAL TISSUE. In nearly all these squamules the cortex is of 

the "decomposed" type. In a few species there is a plectenchymatous 

formation in Cl. nana, a Brazilian ground species, and in two New Zealand 

species, CL enantia f. dilatata and Cl. Neo-Zelandica. The principal growing 

area is situated all round the margins though generally there is more activity 

at the apex. Frequently there is a gradual perishing of the squamule at the 

base which counterbalances the forward increase. 

The upper surface in some species is cracked into minute areolae; the 

cracks, seen in section, penetrate almost to the base of the decomposed 

gelatinous cortex. They are largely due to alternate swelling and contraction 

of the gelatinous surface, or to extension caused, though rarely, by intercalary 

growth from the hyphae below. The surface is subject to weathering and 

peeling as in other lichens; but the loss is constantly repaired by the upward 

growth of the meristematic hyphae from the gonidial zone ; they push up 

1 Wainio 1880.

STRATOSE-RADIATE THALLUS 113 

between the older cortical filaments and so provide for the expansion as 

well as for the renewal of the cortical tissue. 

b. GONIDIAL TISSUE. The gonidia consisting of Protococcaceous algae 

form a layer immediately below the cortex. Isolated green cells are not 

unfrequently carried up by the growing hyphae into the cortical region, but 

they do not long survive in this compact non-aerated tissue. Their empty 

membranes can however be picked out by the blue stain they take with 

iodine and sulphuric acid. 

Krabbe 1 has described the phases of development in the growing region : 

he finds that differentiation into pith, gonidial zone and cortex takes place 

some little way back from the edge. At the extreme apex the hyphae lie 

fairly parallel to each other; further back, they branch upwards to form the 

cortex, and to separate the masses of multiplying gonidia, by pushing 

between them and so spreading them through the whole apical tissue. The 

gonidia immediately below the upper cortex, where they are well-lighted, 

continue to increase and gradually form into the gonidial zone; those that 

lie deeper among the medullary hyphae remain quiescent, and before long 

disappear altogether. 

Where the squamules assume the upright position (as in Cladonia cei~vi- 

corms), there is a tendency for the gonidia to pass round to the lower 

surface, and soredia are occasionally formed. 

c. MEDULLARY TISSUE. The hyphae of the medulla are described by 

Wainio as having long cells with narrow lumen, and as being encrusted 

with granulations that may coalesce into more or less detachable granules; 

in colour they are mostly white, but pale-yellow in Cl.foliacea and blood-red 

in Cl. miniata, a subtropical species. They are connected at the base of the 

squamules with a filamentous hypothallus which penetrates the substratum 

and attaches the plant. In a few species rhizinae are formed, while in others 

the hyphae of the podetium grow downwards, towards and into the sub- 

stratum as a short stout rhizoid. 

d. SOREDIA. Though frequent on the podetia, soredia are rare on the 

squamules, and, according 

to Wainio 2 

, always originate at the growing 

region, from which they spread over the under surface rather sparsely in 

Cl. cariosa, Cl. squamosa, etc., but abundantly in Cl. digitata and a few others. 

In some instances, they develop further into small corticate areolae on the 

under surface (Cl. cocci/era, Cl. pyxidata and Cl. squamosd). 


2 Wainio 1897.

II4 

2. 

MORPHOLOGY 

RADIATE OR SECONDARY THALLUS 

A. ORIGIN OF THE PODETIUM 

The upright podetium, as described by Wainio 1 and by 

2 Krabbe , is a 

secondary product of the basal granule or squamule. It is developed from 

the hyphae of the gonidial zone, generally where a crack has occurred in the 

cortex and rather close to the base or more rarely on or near the edge of 

the squamule (Cl. verticillata, etc.). At these areas, 

certain meristematic 

gonidial hyphae increase and unite to form a strand of filaments below the 

upper cortex but above the gonidial layer, the latter remaining for a time 

undisturbed as to the arrangement of the algal cells. 

This initial tissue the primordium of the podetium continues to grow 

not only in width but in length: the basal portion grows downwards and 

at length displaces the gonidial zone, while the upper part as a compact 

cylinder forces its way through the cortex above, the cortical tissue, however, 

taking no part in its formation ; as it advances, the edges of the gonidial 

and cortical zones bend upwards and form a sheath distinguishable for some 

time round the base of the emerging podetium. 

Even when the primary horizontal thallus is merely crustaceous, the 

podetia take origin similarly from a subcortical weft of hyphae in an areola 

or granule. 

B. STRUCTURE OF THE PODETIUM 

a. GENERAL STRUCTURE. In the early stages of development the 

podetium is solid throughout, two layers of tissue being discernible the 

hyphae forming the centre of the cylinder being thick-walled and closely 

compacted, and the hyphae on the exterior loosely branching with numerous 

air-spaces between the filaments. 

In all species, with the exception of Cl. solida, which remains solid during 

the life of the plant, a central cavity arises while the podetium is still quite 

short (about i to i - 

5 mm. in Cl. pyxidata and Cl. degenerans). The first 

indication of the opening is a narrow split in the internal cylinder, due to 

the difference in growth tension between the more free and rapid increase 

of the external medullary layer and the slower elongation of the chondroid 

tissue at the centre. The cavity gradually widens and becomes more com- 

pletely tubular with the upward growth of the podetium ; it is lined by 

the chondroid sclerotic band which supports the whole structure (Fig. 67). 

b. GONIDIAL TISSUE. In most species of Cladoniaceae, a layer of goni- 

dial tissue forms a more or less continuous outer covering of the podetium, 

1 Wainio 1880. 2 Krabbe 1891.

STRATOSE-RADIATE THALLUS 

thus distinguishing it from the purely hyphal stalks of the apothecia in 

Caliciaceae. Even in the genus Baeomyces, 

while the podetia of some of the species 

are without gonidia, neighbouring species 

are provided with green cells on the upright 

stalks clearly showing their true 

affinity with the Cladoniae. In one British 

species of Cladonia {Cl. caespiticia) the 

short podetium consists only of the fibrous 

chondroid cylinder, and thus resembles the 

apothecial stalk of Baeomyces rufus, but 

in that species also there are occasional 

surface gonidia that may give 

rise to 

squamules. 

Krabbe 1 concluded from his observa- 

tions that the podetial gonidia of Cladonia 

arrived from the open, conveyed by wind, 

water or insects from the loose sored ia that 

are generally so plentiful in any Cladonia 

colony. They alighted, he held, on the 

growing stalks and, being secured by the 

free-growing ends of the exterior hyphae, 

they increased and became an integral part of the podetium. In more 

recent times Baur 2 has recalled and supported Krabbe's view, but Wainio 3 

stage of central tube and of podetial 

squamulesx 100 (after Krabbe). 

on the contrary, claims to have proved that in the earliest stages of the 

podetium the gonidia were already present, having been carried up from 

the gonidial zone of the primary thallus by the primordial hyphae. Increase 

of these green cells follows normally by cell-division or sporulation. 

Algal cells have been found to be common to different lichens, but in 

Cladoniae Chodat 4 claims to have proved by cultures that each species 

tested has a special gonidium, determined by him as a species of Cystococcus, 

which would render colonization by algae from the open much less probable. 

In addition, the fungal hyphae are specific, and any soredia (with their 

combined symbionts) that alighted on the podetium could only be utilized 

if they originated from the same species; or, if they were incorporated, the 

hyphae belonging to any other species would of necessity die off and be 

replaced by those of the podetium. 

c. CORTICAL TISSUE. In some species a cortex of the decomposed type 

of thick-walled conglutinate hyphae is present, either continuous over the 

whole surface of the podetium, as in Cl. gracilis (Fig. 68), or in interrupted 

1 Krabbe t! 

2 Baur 1904. 

3 Wainio 1880. Chodat 1913. 

82 

,

MORPHOLOGY 

Fig. 68. Cladonia gracilis Hoffm. (S. H., Photo.). 

Fig. 69. Cladonia pyxtdata Hoftm. (S. H., Photo.]


areas or granules as in Cl. pyxidala (Fig. 69) and others. In Cl. degenerans, 

the spaces between the corticated areolae are filled in by loose filaments 

without any green cells. CL rangiferina, Cl. sylvatica, etc. are non-corticate, 

being covered all over with a loose felt of intricate hyphae. 

In the section Clathrinae (Cl. retepora, etc.) the cortex is formed of 

longitudinal hyphae with thick gelatinous walls. 

d. SOREDlA. Frequently the podetium is coated in whole or in part by 

granules of a sorediate character coarsely granular in Cl. pyxidata, finely 

pulverulent in CL fimbriata. Though fairly constant to type in the different 

species, they are subject to climatic influences, and, when there is abundant 

moisture, both soredia and areolae develop into squamules on the podetium. 

A considerable number of species have thus a more or less densely squamu- 

lose "form" or "variety." 

C. DEVELOPMENT OF THE SCYPHUS 

Two types of podetia occur in Cladonia : those that end abruptly and 

are crowned when fertile by the apothecia or spermogonia (pycnidia), or if 

sterile grow indefinitely tapering gradually to a point (Fig. 70); 

Fig. 70. Cladonia furcata Schrad. Sterile thallus (S.H., Photo.']. 

and those 

that widen out into the trumpet-shaped or cup-like expansion called the 

scyphus (Fig. 69). Species may be constantly scyphiferous or as constantly 

ascyphous; in a few species, and even in individual tufts, both types of 

podetium may be present.

n8 MORPHOLOGY 

Wainio 1 

, 

who has studied every stage of development in the Cladoniae, 

has described the scyphus as originating in several different ways: 

a. FROM ABORTIVE APOTHECIA. In certain species the apothecium 

appears at a very early stage in the development of the podetium of which 

it occupies the apical region. Owing to the subsequent formation of the 

tubular cavity in the centre of the stalk, the base of the apothecium may 

eventually lie directly over the hollow space and, therefore, out of touch 

with the growing assimilating tissues; or even before the appearance of the 

tube, the wide separation between the primordium of the apothecium and 

the gonidia, entailing deficient nutrition, may have produced a similar effect. 

In either case central degeneration of the apothecium sets in, and the 

hypothecial filaments, having begun to grow radially, continue to travel in 

the same direction both outwards and upwards so that gradually a cup- 

of the fruit without the 

shaped structure is evolved the thecium. 

amphithecium 

The whole or only a part of the apothecium may be abortive, and the 

scyphus may therefore be entirely sterile or the fruits may survive at the 

edges. The apothecia may even be entirely abortive after a fertile commencement, 

but in that case also the primordial hyphae retain the primitive 

impulse not only to radial direction, but also to the more copious branching, 

and a scyphus is formed as in the previous case. It must also be borne in 

mind that the tendency in many Cladonia species to scyphiform has become 

hereditary. 

Baur 2 

, 

in his study of Cl. pyxidata, has taken the view that the origin of 

the scyphus was due to a stronger apical growth of the hyphae at the 

circumference than over the central tubular portion of the podetium, and 

that considerable intercalary growth added to the expanding sides of the cup. 

Scyphi originating from an abortive apothecium are characteristic of 

species in which the base is closed (Wainio's Section Clausae\ the tissue in 

that case being continuous over the inside of the cup as in Cl. pyxidata, 

CL cocci/era and many others. 

b. FROM POLYTOMOUS BRANCHING. Another method of scyphus forma- 

tion occurs in Cl. amaurocrea and a few other species in which the branching 

is polytomous (several members rising from about the same level). Con- 

crescence of the tissues at the base of these branches produces a scyphus ; 

it is normally closed by a diaphragm that has spread out from the different 

bases, but frequently there is a perforation due to stretching. These species 

to the Section Perviae. 

belong 

c. FROM ARRESTED GROWTH. In most cases however where the 

scyphus is open as in Cl.furcata, Cl. sguamosa, etc., development of the cup 

1 Wainio 1897. 

2 Baur 1904.


follows on cessation of growth, or on perforation at the summit of the 

podetium. Round this quiescent portion there rises a circle of minute 

prominences which carry on the apical development. As they increase in 

size, the spaces between them are bridged over by lateral growth, and the 

scyphus thus formed is large or small according to the number of these 

outgrowths. Apothecia or spermogonia may be produced at their tips, or 

the vegetative development may continue. Scyphi formed in this manner 

are also open or "pervious." 

d. GONIDIA OF THE SCYPHUS. Gonidia are absent in the early stages 

of scyphus formation when it arises from degeneration of the apical 

tissues, either fertile or vegetative ; but gradually they migrate from the 

podetium, from the base of young outgrowths, or by furrows at the edge, and 

so spread over the surface of the cup. Soredia may possibly alight, as 

Krabbe insists that they do, and may aid in colonizing 

the naked area. 

Their presence, however, would only be accidental ; they are not essential, 

and scyphi are formed in many non-sorediate species such as Cl. vertidllata. 

The cortex of the scyphus becomes in the end continuous with that of the 

podetium and is always similar in type. 

e. SPECIES WITHOUT SCYPHI. In species where the whole summit of 

the podetium is occupied by an apothecium, as in Cl. bellidiflora, no scyphus 

is formed. There is also an absence of scyphi in podetia that taper to a 

point. In those podetia the hyphae are parallel to the long axis and remain 

in connection with the external gonidial layer so that they are unaffected 

by the central cavity. Instances of tapering growth are also to be found 

in species that are normally scyphiferous such as Cl. fimbriata subsp. jil?u/a, 

and Cl. cornuta, as well as in species like Cl. rangiferina that are constantly 

ascyphous. 

The scyphus is considered by Wainio 1 to represent an advanced stage 

of development in the species or in the individual, and any conditions that 

act unfavourably on growth, such as excessive dryness, would also hinder 

the formation of this peculiar lichen structure. 

D. BRANCHING OF THE PODETIUM 

Though branching is a constant feature in many species, regular dichotomy 

is rare; more often there is an irregular form of polytomy in which one 

of the members grows more vigorously than the others and branches again, 

so that a kind of sympodium arises, as in Cl. rangiferina, Cl. sylvatica, etc. 

Adventitious branches may also arise from the podetium, owing to some 

disturbance of the normal growth, some undue exposure to wind or to too 

i Wainio 1897.

120 

MORPHOLOGY 

great light, or owing to some external injury. They originate 

from the 

gonidial tissue in the same way as does the podetium from the primary 

thallus; the parallel hyphae of the main axis take no part in their development. 

In a number of species secondary podetia arise from the centre of the 

scyphus constantly in Cl. verticillata and Cl. cervicornis, etc., accidentally 

or rarely in Cl. foliacea, Cl. pyxidata, CL fimbriata, etc. Wainio 1 has stated 

that they arise when the scyphus is already at an advanced stage of growth 

and that they are to be regarded as adventitious branches. 

The proliferations from the borders of the scyphus are in a different 

category. They represent the continuity of apical growth, as the edges of 

the scyphus are but an enlarged apex. These marginal proliferations thus 

correspond to polytomous branching. In many instances their advance is 

soon stopped by the formation of an apothecium and they figure more as 

fruit stalks than as podetial branches. 

E. PERFORATIONS AND RETICULATION OF THE PODETIUM 

Perforations in the podetial wall at the axils of the branches are constant 

in certain species such as Cl. rangiferina, CL uncialis, etc. They are caused 

by the tension of the branches as they emerge from the main stalk. 

A tearing of the tissue may also arise in the base of the scyphus, due to its 

increase in size, which causes the splitting of the diaphragm at the bottom 

of the cup. 

Among the Cladoniae the reticulate condition recurs now and again. 

In our native Cladonia cariosa the splitting of the podetial wall is a constant 

character of the species, the carious condition being caused by unequal 

growth which tears apart the longitudinal fibres that surround the central 

hollow. 

A more advanced type of reticulation arises in the group of the Clathrinae 

in which there is no inner chondroid cylinder. In Cladonia aggregata, in 

which the perforations are somewhat irregular, two types of podetia have 

been described by Lindsay 2 from Falkland Island specimens: those bearing 

apothecia are short and broad, fastigiately branched upwards and with 

reticulate perforations, while podetia bearing spermogonia are slender, elon- 

gate and branched, with fewer reticulations. An imperfect network is also 

characteristic of CL Sullivani, a Brazilian species. But the most marvellous 

and regular form of reticulation occurs in Cl. retepora, an Australian lichen 

(Fig. 71): towards the tips of the podetia the ellipsoid meshes are small, 

but they gradually become larger towards the base. In this species the 

outer tissue, though of parallel hyphae, is closely interwoven and forms 


2 

Lindsay 1859, P- 171-


a continuous growth at the edges of the perforations, giving an unbroken 

smooth surface and checking any irregular tearing. The enlargement of 

the walls is solely due to intercalary growth. The origin of the reticulate 

structure in the Clathrinae is unknown, though 

Fig. 71. Cladonia retepora Fr. From Tasmania. 

it is doubtless associated 

with wide podetia and rendered possible by the absence of an internal 

chondroid layer. The reticulate structure is marvellously adapted for the 

absorption of water: Cl. retepora, more especially, imbibes and holds moisture 

like a sponge. 

F. ROOTING STRUCTURES OF CLADONIAE 

The squamules of the primary thallus are attached, as are most squamules, 

to the supporting substance by strands of hyphae which may be 

combined into simple or branching rhizinae and penetrate the soil or the 

wood on which the lichen grows. There is frequently but one of these 

rooting structures and it branches repeatedly until the ultimate branchlets 

end in delicate mycelium. Generally they are grey or brown and are not

122 ' MORPHOLOGY 

easily traced, but when they are orange-coloured, as according 

they frequently are in Cladonia miniata and Cl. digitata, they 

to Wainio 1 

are more 

readily observed, especially if the habitat be a mossy one. 

In Cl. alpicola it has been found that the rooting structure is frequently 

as thick as the podetium itself. If the podetium originates from the basal 

portion of the squamule, the hyphae from the chondroid layer, surrounding 

the hollow centre, take a downward direction and become continuous with 

the rhizoid. Should the point of insertion be near the apex of the squamule, 

these hyphae form a nerve within the squamule or along the under surface, 

and finally also unite with the rhizoid at the base, a form of rooting charac- 

teristic of Cl. cartilaginea, Cl. digitata and several other species. 

Mycelium may spread from the rhizinae along the surface of the substratum 

and give rise to new squamules and new tufts of podetia, a method 

of reproduction that is of considerable importance in species that are 

generally sterile and that form no soredia. 

Many species, especially those of the section Cladina, soon lose all 

connection with the substratum, there being a continual decay of the lower 

part of the podetia. As apical growth may continue for centuries, the 

perishing of the base is not to be wondered at. 

G. HAPTERA 

The presence of haptera in Cladoniae has already been alluded to. They 

occur usually in the form of cilia or rhizinae 2 

, but differ from the latter in 

their more simple regular growth being composed of conglutinate parallel 

hyphae. They arise on the edges of the squamules or of the scyphus, but 

in Cl. foliacea and Cl. ceratophylla they are formed at the points of the 

podetial branches (more rarely in Cl. cervicornis and Cl. gracilis). By the aid 

of these rhizinose haptera the squamule or branch becomes attached to any 

substance within reach. They also aid in the production of new individuals 

by anchoring some fragment of the thallus to a support until it has grown 

to independent existence and has produced new rhizinae or holdfasts. They 

are a very prominent feature of Cl. verticillaris f. penicillata in which they 

form a thick fringe on the edges of the squamules, or frequently grow out 

as branched cilia from the proliferations on the margins of the scyphus. 

H. MORPHOLOGY OF THE PODETIUM 

In the above account, the podetia have been treated as part of the 

vegetative thallus, seeing that, partly or entirely, they are assimilative and 

absorptive organs. This view does not, however, take into account their 

origin and development, in consideration of which Wainio 3 and later Krabbe 4 


2 Wainio l897) p< 9 

3 Wainio I8g0i 4 Krabbe ,g 9r>


considered them as part of the sporiferous organ. This view was also held 

by some of the earliest lichenologists: Necker 1 

, for instance, constantly 

referred to the upright structure as "stipes"; Persoon 2 included it, under 

the term "pedunculus," as part of the "inflorescence" of the lichen, and 

Acharius 3 established the name "podetium" to describe the stalk of the 

apothecium in Baeomyces. 

Later lichenologists, such as Wallroth 4 

, looked on the podetia as advanced 

stages of the thallus, or as forming a supplementary thallus. Tulasne 5 

described them as branching upright processes from the horizontal form, 

and Koerber 6 considered them as the true thallus, the primary squamule 

being merely a protothallus. By them and by succeeding students of lichens 

the twofold character of the thallus was accepted until Wainio and Krabbe 

by their more exact researches discovered the endogenous origin 

of the 

podetium, which they considered was conclusive evidence of its apothecial 

character: they claimed that the primordium of the podetium was homolo- 

gous with the primordium of the apothecium. Reinke 7 and Wainio are in 

accord with Krabbe as to the probable morphological significance of the 

podetium, but they both insist on its modified thalline character. Wainio 

sums up that: "the podetium is an apothecial stalk, that is to say an 

elongation of the conceptacle most frequently transformed by metamorphosis 

8 

to a vertical thallus, though visibly retaining its stalk character." Sattler , 

one of the most recent students of Cladonia, regards the podetium as evolved 

with reference to spore-dissemination, and therefore of apothecial character. 

His views are described and discussed in the chapter on phylogeny. 

Reinke and others sought for a solution of the problem in Baeomyces, 

one of the more primitive genera of the Cladoniaceae. The thallus, except 

in a few mostly exotic species, scarcely advances beyond the crustaceous 

condition; the podetia are short and so varied in character that species 

have been assigned by systematists to several different genera. In one of 

them, Baeomyces roseus, the podetium or stalk originates according to 

Nienburg 9 

deep down in the medulla of a fertile granule as a specialized 

weft of tissue; there is no carpogonium nor trichogyne formed ; the hyphae 

that grow upward and form the podetium are generative filaments and give 

rise to asci and paraphyses. In a second species, B. rufus (Sphyridium\ the 

gonidial zone and outer cortex of a thalline granule swell out to form a 

thalline protuberance; the carpogonium arises close to the apex, and from 

it branch the generative filaments. Nienburg regards the stalk of B. roseus 

as apothecial and as representing an extension of the proper margin 10 (ex- 

cipulmn propriuwi), that of B. rufus as a typical vegetative podetium. 

1 Necker 1871. 


9 



i2 4 

MORPHOLOGY 

In the genus Cladonia, differentiation of the generative hyphae may 

observed, in CL caespiticia, a 

take place at a very early stage. Wainio 1 

trichogyne in a still solid podetium only 90 /x in height; usually they appear 

later, and, where scyphi are formed, the carpogonium often arises at the 

edge of the scyphus. Baur 2 and Wolff3 have furnished conclusive evidence 

of the late appearance of the carpogonium in CL pyxidata, Cl. degenerans, 

CL furcata and CL gracilis: in all of these species carpogonia with trichogynes 

were observed on the edge of well-developed scyphi. Baur draws the 

conclusion that the podetium is merely a vertical thallus, citing as additional 

evidence that it also bears the spermogonia (or pycnidia), though at the 

same time he allows that the apothecium may have played an important part 

in its phylogenetic development. He agrees also with the account of the 

first appearance of the podetium as described by Krabbe, who found that 

it began with the hyphae of the gonidial zone branching upwards in a quite 

normal manner, only that there were more of them, and that they finally 

pierced the cortex. Krabbe also asserted that in the early stages the podetia 

were without gonidia and that these arrived later from the open as colonists, 

in this contradicting Wainio's statement that gonidia were carried up from 

the primary thallus. 

It seems probable that the podetium as Wainio and Baur both have 

stated is homologous with the apothecial stalk, though in most cases it is 

completely transformed into a vertical thallus. If the view of their formation 

from the gonidial zone is accepted, then they differ widely in origin from 

normal branches in which the tissues of the main axis are repeated in the 

secondary structures, whereas in this vertical thallus, hyphae from the 

gonidial zone alone take part in the development. It must be admitted 

that Baur's view of the podetium as essentially thalline seems to be strengthened 

by the formation of podetia at the centre of the scyphus, as "in CL 

verticillata, which are new structures and are not an elongation of the 

original conceptacular tissue. It can however equally be argued that the 

acquired thalline character is complete and, therefore, includes the possibility 

of giving rise to new podetia. 

The relegation of the carpogonium to a position far removed from the 

base or primordium of the apothecium need not necessarily interfere with 

the conception of the primordial tissue as homologous with the conceptacle; 

but more research is needed, as Baur dealt only with one species, CLpyxidata, 

and Gertrude Wolff confined her attention to the carpogonial stages at the 

edge of the scyphus. 

The Cladoniae require light, and inhabit by preference open moorlands, 

naked clay walls, borders of ditches, exposed sand-dunes, etc. Those with 

large and persistent squamules can live in arid situations, probably because 


2 Baur 1904. 

3 Wolff 1905.


the primary thallus is able to retain moisture for a long time 1 . When 

the 

primary thallus is small and feeble the podetia are generally much branched 

and live in close colonies which retain moisture. Sterile podetia are long- 

lived and grow indefinitely at the apex though the base as continually 

perishes and changes into humus. Wainio 2 cites an instance in which the 

bases of a tuft of Cl. alpestris had formed a gelatinous mass more than a 

decimetre in thickness. 

I. PlLOPHORUS AND STEREOCAULON 

These two genera are usually included in Cladoniaceae on account 

of their twofold thallus and their somewhat similar fruit formation. 

They differ from Cladonia in the development of the podetia which are 

not endogenous in origin as in that genus, but are formed by the growth 

upwards of a primary granule or squamule and correspond more nearly to 

Tulasne's conception of the podetium as a process from the horizontal 

thallus. In Pilophorus the primary granular thallus persists during the life 

of the plants; the short podetium is unbranched, and consists of a some- 

what compact medulla of parallel hyphae surrounded by a looser cortical 

tissue, such as that of the basal granule, in which are embedded the algal 

cells. The black colour of the apothecium is due to the thick dark hypo- 

thecium. 

Stereocaulon is also a direct growth from a short-lived primary squamule 3 . 

The podetia, called " pseudopodetia " 

by Wainio, are usually very much 

branched. They possess a central strand of hyphae not entirely solid, and 

an outer layer of loose felted hyphae in which the gonidia find place. A 

coating of mucilage on the outside gives a glabrous shiny surface, or, if 

that is absent, the surface is tomentose as in St. tomentosum. In all the 

species the podetia are more or less thickly beset with small variously 

divided squamules similar in form to the primary evanescent thallus. Galllike 

cephalodia are associated with most of the species and aid in the work 

of assimilation. 

Stereocaulon cannot depend on the evanescent primary thallus for attachment 

to the soil. The podetia of the different species have developed various 

rooting bases: in St. ramulosum there is a basal sheath formed, in St. coral- 

hides a well-developed system of rhizoids 4 . 

1 

Aigret 1901. 


3 Wainio 1890, p. 67. 

4 Reinke 1895.

. 

126 MORPHOLOGY 

V. STRUCTURES PECULIAR TO LICHENS 

i. AERATION STRUCTURES 

A. CYPHELLAE AND PSEUDOCYPHELLAE 

The thallus of Stictaceae has been regarded by Nylander 1 

and others as 

one of the most highly organized, not only on account of the size attained 

by the spreading lobes, but also because in that family are chiefly found 

those very definite cup-like structures which were named "cyphellae" by 

Acharius 2 . They are small hollow depressions about \ mm. or more in 

width scattered irregularly over the under surface of the thallus. 

a. HISTORICAL. Cyphellae were first pointed out by the Swiss botanist, 

Haller 3 . In his description of a lichen referable to Sticta fuliginosa he 

" 

describes certain white circular depressions to be found among the short 

brown hairs of the under surface." At a later date Schreber 4 made these 

" white excavated points " the leading character of his lichen genus Sticta. 

In urceolate or proper cyphellae, the base of the depression rests on the 

medulla; the margin is formed from the ruptured cortex and projects slightly 

inwards over the edge of the cup. Contrasted with these are the pseudo- 

cyphellae, somewhat roundish openings of a simpler structure which replace 

the others in many of the species. They have no definite margin ; the inter- 

nal hyphae have forced their way to the exterior and form a protruding 

tuft slightly above the surface. Meyer 5 reckoned them all among soredia; 

but he distinguished between those in which the medullary hyphae became 

conglutinated to form a margin (true cyphellae) and those in which there 

was a granular outburst of filaments (pseudocyphellae). He also included 

a third type, represented in Lobaria pulmonaria on the under surface of 

which there are numerous non-corticate, angular patches where the pith is 

laid bare (Fig. 72). Delise 6 

, writing about the same time on the Sticteae, 

gives due attention to their occurrence, classifying the various species of 

Sticta as cyphellate or non-cyphellate. 

Acharius had limited the name " cyphella " to the hollow urceolate bodies 

that had a well-defined margin. Nylander 7 at first included under that 

term both types of structure, but later 8 he classified the pulverulent " soredia- 

like " forms in another group, the pseudocyphellae. As a rule they bear no 

relation to soredia, and algae are rarely associated with the protruding 

filaments. Schwendener 9 and later Wainio , 10 

Sticta aurata from 

, in describing 

Brazil, state, as exceptional, that the citrine-yellow pseudocyphellae of that 

species are sparingly sorediate. 

1 

Nylander 1858, p. 63. 

4 Schreber 1791, p. 768. 

8 

Nylander 1860, p. 333. 

' 

2 

Acharius 1810, p. 12. 3 Haller 1768, p. 85. 

6 Meyer 1825, p. 148. 


s Delise 1822. 7 Nylander 1858, p. 14. 

10 Wainio 1890, I. p. 183.

STRUCTURES PECULIAR TO LICHENS 127 

b. DEVELOPMENT OF CYPHELLAE. The cortex of both surfaces in the 

thallus of Sticta is a several-layered plectenchyma of thick-walled closely 

Fig. 72. Lobaria pulnionaria Hoffm. Showing pitted surface, a, under surface. 

Reduced (S. H., Photo.}. 

packed cells, the outer layer growing out into hairs on the under surface of 

most of the species. Where either cyphellae or pseudocyphellae occur, a 

more or less open channel is formed between the exterior and the internal 

tissues of the lichen. In the case of the cyphellae, the medullary hyphae 

which line the cup are divided into short roundish cells with comparatively 

thin -walls (Fig. 73). They form a tissue sharply differentiated from the 

Fig. 73. Sticta damaecornis Nyl. Transverse section 

of thallus with cyphella x 100. 

loose hyphae that occupy the medulla. The rounded cells tend to lie in 

vertical rows, though the arrangement in fully formed cyphellae is generally

128 MORPHOLOGY 

somewhat irregular. The terminal empty cells are, loosely attached and as 

they are eventually abstricted and strewn over the inside of the cup they 

give to it the characteristic white powdery appearance. 

1 

According to Schwendener 

development begins by an exuberant growth 

of the medulla which raises and finally bursts the cortex; prominent cyphellae 

have been thus formed in Sticta damaecornis (Fig. 73). In other species 

the swelling is less noticeable or entirely absent. The opening of the cup 

measures usually about \ mm. across, but it may stretch to a greater width. 

c. PsEUDOCYPHELLAE. In these no margin is formed, the cortex is 

simply burst by the protruding filaments which are of the same colour 

yellow or white as the medullary hyphae. They vary in size, from a minute 

point up to 4 mm. in diameter. 

d. OCCURRENCE AND DISTRIBUTION. The genus Sticta is divided into 

two sections : (i) Eusticta in which the gonidia are bright-green algae, and 

(2) Stictina in which they are blue-green. Cyphellae and pseudocyphellae 

are fairly evenly distributed between the sections; they never occur together. 

Stizenberger 2 found that 36 species of the section Eusticta were cyphellate, 

while in 43 species pseudocyphellae were formed. In the section Stictina 

there were 38 of the former and only 31 of the latter type. Both sections of 

the genus are widely distributed in all countries, but they are most abundant 

south of the equator, reaching their highest development in Australia and 

New Zealand. 

In the British Isles Sticta is rather poorly represented as follows: 

\Eusticta (with bright-green gonidia). 

Cyphellate: 5. damaecornis. 

Pseudocyphellate: S. aurata. 

\Stictina (with blue-green gonidia). 

Cyphellate: S.fidiginosa, S. limbata, S. sylvatica, S. Dufourei. 

Pseudocyphellate: 5. intricata van Thouarsii, S. crocata. 

Structures resembling cyphellae, with an overarching rim, are sprinkled 

over the brown under surface of the Australian lichen, Heterodea Miilleri; 

the thallus is without a lower cortex, the medulla being protected by thickly 

woven hyphae. Heterodea was at one time included among Stictaceae, 

though now it is classified under Parmeliaceae. Pseudocyphellae are also 

present on the non-corticate under surface of Nephromium tomentosum, 

where they occur as little white pustules among the brown hairs; and the 

white impressed spots on the under surface of Cetraria Islandica and allied 

species, first determined as air pores by Zukal 3 have also , been described by 

Wainio 4 as pseudocyphellae. 


2 

Stizenberger 1895. 

3 Zukal 1895, p. 1355. 

4 Wainio 1909.


There seems no doubt that the chief function of these various structures 

1 

is, as Schwendener 

suggested, to allow a free passage of air to the assimi- 

lating gonidial zone. Jatta 2 considers them to be analogous to the lenticels 

of higher plants and of service in the interchange of gases expelling car- 

bonic acid and receiving oxygen from the outer atmosphere. It is remarkable 

that such serviceable organs should have been evolved in so few lichens. 

B. BREATHING-PORES 

a. DEFINITE BREATHING-PORES. The cyphellae and pseudocyphellae 

described above are confined to the under surface of the thallus in those 

lichens where they occur. Distinct breathing-pores of a totally different 

structure are present on the upper 

surface of the tree-lichen, Parmelia 

aspidota (P. exasperata}, one of the 

brown-coloured species. They are 

somewhat thickly scattered as isidia- 

or cone-like warts over the lichen 

thallus (Fig. 74) and give it the char- 

acteristically rough or "exasperate" 

character. They are direct outgrowths 

from the thallus, and Zukal 3 who dis- 

covered their peculiar nature and func- 

, 

4. Parmelia exasperata Carroll. Vertical 

section of thallus. a, breathing- pores; 

l>, rhizoid. x 60 (after Rosendahl). 

tion, describes them as being filled with a hyphal tissue, with abundant 

air-spaces, and in direct communication with the medulla ; gonidia, if 

present, are confined to the basal part. The cortex covering these minute 

cones, he further states, is very thin on the top, or often wanting, so that 

a true is pore formed which, however, is only opened after the cortex else- 

where has become thick and horny. Rosendahl 4 

, 

who has re-examined these 

"breathing-pores," finds that in the early stage of their growth, near the 

margin or younger portion of the thallus, they are entirely covered by the 

cortex. Later, the hyphae at the top become looser and more frequently 

septate, and a fine net-work of anastomosing and intricate filaments takes 

the place of the closely cohering cortical cells. These hyphae are divided 

into shorter cells, but do not otherwise differ from those of the medulla. 

Rosendahl was unable to detect an open pore at any stage, though he 

entirely agrees with Zukal as to the breathing function of these structures. 

The gonidia of the immediately underlying zone are sparsely arranged and 

a few of them are found in the lower half of the cone; the hyphae of the 

medulla can be traced up to the apex. 

S. L. 

Schwendener 1863, p. 169. 

2 Jatta 1889, p. 4* 


3 Zukal 1895, p. 1357-

130 

MORPHOLOGY 

Zukal 1 claims to have found breathing-pores in Cornicularia (Parmelid) 

Fig. 75 A. Ramalina fraxinea Ach. 

A, surface view of frond, a, airres; 

/>, young x \i. 

apothecia. 

transverse section of . part of 

frond, a, breathing-pore \f, strengthening 

fibres, x 37 (after Brandt). 

tristis and in several other Parmeliae, notably 

in Parmelia stygia. The thallus of the latter 

species has minute holes or openings in the 

upper cortex, but they are without any definite 

form and may be only fortuitous. 

Zukal 1 

published drawings of channels of 

looser tissue between the exterior and the 

pith in Oropogon Loxensis and in Usnea barbata. 

He considered them to be of definite 

service in aeration. The fronds of Ramalina 

dilacerata by stretching develop a series of 

elongate holes. Reinke 2 found openings in 

Ramalina Eckloni which pierced to the centre 

of the thallus, and Darbishire 3 has figured 

a break in the frond of another species, R. 

fraxinea (Fig. 75 A), which he has designated 

as a breathing-pore. Finally Brandt 4 

careful study of the anatomy of Ramalinae, 

has described as breathing- pores certain open 

areas usually of ellipsoid form in the compact 

cortex of several species: in R. strepsilis 

(Fig. 75 B) and R. Landroensis, and in the 

British species, R. siliquosa and R. fraxinea. These openings are however 

mostly rare and difficult to find or to distinguish from holes that may 

be due to any accident in the life of the lichen. It is noteworthy that 

Fig- 75 B- Ramalina strepsilis Zahlbr. Transverse section 

of part of frond showing distribution of: a, air-pores, and 

f, strengthening fibres, x 37 (after Brandt). 

Rosendahl found no further examples of breathing-pores in the brown 

Parmeliae that he examined in such detail. No other organs specially 

adapted for aeration of the thallus have been discovered. 

b. OTHER OPENINGS IN THE THALLUS. Lobaria is the only genus of 

Stictaceae in which neither cyphellae nor pseudocyphellae are formed but 

; 

in two species, L. scrobiculata and L. pulmonaria, the lower surface is marked 

1 Zukal 1895. 

2 Reinke 1895, p. 183. 



, in his


with oblong or angular bare convex patches, much larger than cyphellae. 

They are exposed portions of the medulla, which at these spots has been 

denuded of the covering cortex. Corresponding with these bare spots there 

is a pitting of the upper surface. 

A somewhat similar but reversed structure characterizes Umbilicaria 

pustulata, which as the name implies is distinguished by the presence of 

pustules, ellipsoid swellings above, with a reticulation of cavities below. 

Bitter 1 in this instance has proved that they are due to disconnected centres 

of intercalary growth which are more vigorous on the upper surface and 

give rise to cracks in the less active tissue beneath. These cracks gradually 

become enlarged ; they are, as it were, accidental in origin but are doubtless 

of considerable service in aeration. 

In some Parmeliae there are constantly formed minute round holes, 

either right through the apothecia (P. cetrata, etc.), or through the thallus 

(P. pertusd). Minute holes are also present in the under cortex of Parmelia 

vittata and of P. enteromorpha, species of the subgenus Hypogymnia. 

Nylander 2 

, who first drew attention to these holes of the lower cortex, 

described them as arising at the forking of two lobes ; but though they do 

occur in that position, they as frequently bear no relation to the branching. 

Bitter's 3 

opinion is that they arise by the decay 

of the cortical tissues in 

very limited areas, from some unknown cause, and that the holes that pierce 

right through the thallus in other species may be similarly explained. 

Still other minute openings into the thallus occur in Parmelia vittata, 

P. obscurata and P. farinacea var. obscurascens. In the two latter the openings 

like pin-holes are terminal on the lobes and are situated exactly on 

the apex, between the pith and the gonidial zone; sometimes several holes 

can be detected on the end of one lobe. Further growth in length is checked 

by these holes. They appear more frequently on the darker, better illuminated 

plants. In Parmelia vittata the terminal holes are at the end of 

excessively minute adventitious branches which arise below the gonidial 

zone on the margin of the primary lobes. All these terminal holes are 

directed upwards and are visible from above. 

Bitter does not attribute any physiological significance to these very 

definite openings in the thallus. It has been generally assumed that they 

aid in the aeration of the thallus; it is also possible that they may be of 

service in absorption, and they might even be regarded as open water con- 

ductors. 


2 Nylander i874 2 . 

3 Bitter i9Oi 2 . 

9-2

I32 

MORPHOLOGY 

C. GENERAL AERATION OF THE THALLUS 

Definite structures adapted to secure the aeration of the thallus in a 

limited number of lichens have been described above. These are the breathingpores 

of Parmelia exasperata and the cyphellae and pseudocyphellae of the 

Stictaceae, with which also may be perhaps included the circumscribed 

breaks in the under cortex in some members of that family. 

Though lichens are composed of two actively growing organisms, the 

symbiotic plant increases very slowly. The absorption of water and mineral 

salts must in many instances be of the scantiest and the formation of carbohydrates 

by the deep-seated chlorophyll cells of correspondingly small 

amount. Active aeration seems therefore uncalled for though by no means 

excluded, and there are many indirect channels by which air can penetrate 

to the deeper tissues. 

In crustaceous forms, whether corticate or not, the thallus is often deeply 

seamed and cracked into areolae, and thus is easily pervious to water and 

air. The growing edges and growing points are also everywhere more or 

less loose and open to the atmosphere. In the larger foliose and fruticose 

lichens, the soredia that burst an opening in the thallus, and the cracks 

that are so frequent a feature of the upper cortex, all permit of gaseous 

interchange. The apical growing point of fruticose lichens is thin and porous, 

and in many of them the ribs and veins of their channelled surfaces entail 

a straining of the cortical tissue that results in the formation of thinner 

permeable areas. Zukal 1 devoted special attention to the question of aeration, 

and he finds evidenceof air-passages through empty spermogonia and through 

the small round holes that are constant in the upper surface of certain foliose 

species. He claims also to have proved a system of air-canals right through 

the thallus of the gelatinous Collemaceae. Though his proof in this instance 

is somewhat unconvincing, he establishes the abundant presence of air in 

the massively developed hypothecium of Collema fruits. He found that the 

carpogonial complex of hyphae was always well supplied with air, and that 

caused him to view with favour the suggestion that the function of the 

trichogyne is to provide an air-passage. In foliose lichens, the under surface 

is frequently non-corticate, in whole or in part; or the cortex becomes 

seamed and scarred with increasing expansion, the growth in the lower 

layers failing to keep pace with that of the overlying tissues, as in Umbilicaria 

pustulata. 

It is unquestionable that the interior of the thallus of most lichens con- 

tains abundant empty spaces between the loose-lying hyphae, and that these 

spaces are filled with air. 

1 Zukal 1895, p. 1348.


2. CEPHALODIA 

A. HISTORICAL AND DESCRIPTIVE 

The term " 

cephalodium" was first used 1 

by Acharius to designate certain 

globose apothecia (pycnidia). At a later date he applied it to the 

peculiar outgrowths that grow on the thallus of Peltigera aphthosa, already 

described by earlier writers, along with other similar structures, as " cor- 

puscula," " maculae," etc. The term is now restricted to those purely vegetative 

gall-like growths which are in organic connection with the thallus of 

the lichen, but which contain one or more algae of a different type from the 

one present in the gonidial zone. They are mostly rather small structures, 

and they take various forms according to the lichen species on which they 

occur. They are only found on thalli in which the gonidia are bright-green 

algae (Chlorophyceae) and, with a few exceptions, they contain only blue- 

green (Myxophyceae). Cephalodia with bright-green algae were found by 

Hue 2 on two Parmeliae from Chili, in addition to the usual blue-green forms; 

the one contained Urococcus, the other Gloeocystis. Several with both types 

of algae were detected also by Hue 2 within the thallus of Aspicilia spp. 

Florke 3 in his account of German lichens described the cephalodia that 

grow on the podetia of Stereocaulon as fungoid bodies, "corpuscula fungosa." 

Wallroth 4 who had made a , special study of lichen gonidia, finally established 

that the distinguishing feature of the cephalodia was their gonidia which 

differed in colour from those of the normal gonidial zone. He considered 

that the outgrowths were a result of changes that had arisen in the epidermal 

tissues of the lichens, and, to avoid using a name of mixed import such as 

" 

cephalodia," he proposed a new " 

designation, calling them phymata " or 

warts. 

Further descriptions of cephalodia were given by Th. M. Fries 5 in his 

Monograph of Stereocaulon and Pilophorus\ but the greatest advance in 

the exact knowledge of these bodies is due to Forssell 6 who made a com- 

prehensive examination of the various types, examples of which occurred, 

he found, in connection with about TOO different lichens. Though fairly 

constant for the different species, they are not universally so, and are some- 

times very rare even when present, and then difficult to find. A striking 

instance of variability in their occurrence is recorded for Ricasolia amplissima 

(Lobaria laciniatd) (Fig. 76). The cephalodia of that species are 

prominent upright branching structures which grow in crowded tufts irregu- 

larly scattered over the surface. They are an unfailing and conspicuous 

specific character of the lichens in Europe, but are entirely wanting in North 

American specimens. 


4 Wallroth 1825, p. 678. 

2 Hue 1904 and 1910. 

5 Th. M. Fries 1858. 

3 Florke 1815, IV. p. 15. 

6 Forssell 1884.

134 

MORPHOLOGY 

As cephalodia contain rather dark-coloured, blue-green algae, they are 

nearly always noticeably darker than the thalli on which they grow, varying 

from yellowish-red 

or brown in those of Lecanora gelida to pale-coloured in 

Fig. 76. Ricasolia amplissima de Not. (Lobaria ladniata Wain.) on oak, reduced. The dark 

patches are tufts of branching cephalodia (A. Wilson, Photo.}. 

Lecidea consentiens^ , a 

darker red in Lecidea panaeola and various shades 

of green, grey or brown in Stereocanlon, Lobaria (Ricasolia}, etc. They form 

either flat expansions of varying size on the upper surface of the thallus, 

rounded or wrinkled wart-like growths, or upright branching structures. 

On the lower surface, where they are not unfrequent, they take the form of 

small brown nodules or swellings. In a number of species packets of blue- 

green algae surrounded by hyphae are found embedded in the thallus, 

either in the pith or immediately under the cortex. They are of the same 

nature as the superficial excrescences and are also regarded as cephalodia. 

1 

Leigh ton 1869.


B. CLASSIFICATION 

Forssell has drawn up a classification of these structures, as follows : 

I. CEPHALODIA VERA. 

1. Cephalodia epigena (including perigena) developed on the upper 

outer surface of the thallus, which are tuberculose, lobulate, clavate or 

branched in form. These are generally corticate structures. 

2. Cephalodia hypogena which are developed 

on the under surface 

of the thallus; they are termed "thalloid" if they are entirely superficial, 

and "immersed" when they are enclosed within the tissues. They are noncorticate 

though surrounded by a weft of hyphae. Forssell further includes 

here certain placodioid (lobate), granuliform and fruticose forms which 

develop on the hypothallus of the lichen, and gradually push their way up 

either through the host thallus, or, as in Lecidea panaeola, between the thalline 

granules. 

Nylander 1 

arranged the cephalodia known to him in three groups: 

(i) Ceph. epigena, (2) Ceph. hypogena and (3) Ceph. endogena. 

Schneider 2 

still more simply and practically describes them as Ectotrophic (external), 

and Endotrophic (internal). 

II. PSEUDOCEPHALODIA. 

These are a small and doubtful group of cephalodia which are apparently 

in very slight connection with the host thallus, and show a tendency to 

independent growth. They occur as small scales on Solorina bispora 3 and 

vS". spongiosa and also on Lecidea pallida. Forssell has suggested that the 

cephalodia of Psoroma hypnorum and of Lecidea panaeola might also be included 

under this head. 

Forssell and others have found and described cephalodia in the following 

families and genera: 

Sphaerophoraceae. 

Sphaerophorus (S. stereocauloides). 

Lecideaceae. 

Lecidea (L. panaeola, L, consentiens, L. pelobotrya, etc.). 

Cladoniaceae. 

Stereocaulon, Pilophorus and Argopsis. 

Pannariaceae. 

Psoroma (P. hypnoruiri). 

Peltigeraceae. 

Peltigera (Peltidea), Nephroma and Solorina. 

1 


2 Schneider 1897. 

3 Hue 1910.

i 3 6 

Stictaceae. 

Lobaria, Sticta. 

Lecanoraceae. 

MORPHOLOGY 

Lecania (L. lecanorina), Aspicilia 1 . 

Physciaceae. 

Placodium bicolor*. 

C. ALGAE THAT FORM CEPHALODIA 

The algae of the cephalodia belong mostly to genera that form the 

normal gonidia of other lichens. They are: 

Stigonema, in Lecanora gelida, Stereocaulon, Pilophorus robustus, and 

Lecidea pelobotrya. 

Scytonema, a rare constituent of cephalodia. 

Nostoc.. the most frequent gonidium of cephalodia. It occurs in those 

of the genera Sticta, Lobaria, Peltigera, Nephroma, Solorina and Psoroma; 

occasionally in Stereocaulon and in Lecidea pallida. 

Lyngbya and Rivularia, rarely present, the latter in Sticta oregana*. 

Chroococcus and Gloeocapsa, also very rare. 

Scytonema, Chroococcus, Gloeocapsa and Lyngbya are generally found 

in ^combination with some other cephalodia-building alga, though Nylander 4 

found Scytonema alone in the lobulate cephalodia of Sphaerophorus stereo- 

cauloides, a New Zealand lichen, and the only species of that genus in which 

cephalodia are developed; and Hue 1 records Gloeocapsa as forming internal 

cephalodia in two species of Aspicilia, Bornet 5 found Lyngbya associated 

with Scytonema in the cephalodia of Stereocaulon ramulosum, and, in the 

same lichen, Forssell 6 

found, in the several cephalodia of one specimen, 

Nostoc, Scytonema, and Lyngbya, while, in those of another, Scytonema and 

Stigonema were present. In the latter instance these algae were living free 

on the podetium. Forssell 6 also determined two different algae, Gloeocapsa 

magma and Chroococcus tttrg-idus,preseni in a cephalodium on Lecidea panaeola 

var. elegans. 

As a general rule only one kind of alga enters into the formation of the 

cephalodia of any species or genus. A form of Nostoc, for instance, is in- 

variably the gonidial constituent of these bodies in the genera, Lobaria, Sticta, 

etc. In other lichens different blue-green algae, as noted above, may occupy 

the cephalodia even on the same specimen. Forssell finds alternative algae 

occurring in the cephalodia of: 

Lecanora gelida and Lecidea illita contain either Stigonema or Nostoc; 

Lecidea panaeola, with Gloeocapsa, Stigonema or Chroococcus; 

1 Hue 1910. 

2 Tuckerman 1875. 

3 Schneider 1897, p. 58. 

5 Bornet 1873, p. 72. Forssell 1885, p. 24. 

* 

Nylander 1869.


Lecidea pelobotrya, with Stigonema or Nostoc; 

Pilophorus robustus, with Gloeocapsa, Stigonema, or Nostoc. 

Fig. 77. Lecanora gelida Ach. #, lobate cephalodia 

x 1 2 (after Zopf ). 

Riddle 1 has employed cephalodia with their enclosed algae as diagnostic 

characters in the genus Stereocaulon. When the alga is Stigonema, as in 

5. pascJiale, etc., the cephalodia are generally very conspicuous, grey in 

colour, spherical, wrinkled or folded, though sometimes black and fibrillose 

(S. denudatuni). Those containing Nostoc are, on the contrary, minute and 

are coloured verdigris-green (S. tomentosum and 5. alpinuni). 

Instances are recorded of algal colonies adhering to, and even penetrating, 

the thallus of lichens, but as they never enter into relationship with the 

lichen hyphae, they are antagonistic rather than symbiotic and have no 

relation to cephalodia. 

D. DEVELOPMENT OF CEPHALODIA 

a. EcTOTROPHIC. Among the most familiar examples of external cephalodia 

are the small rather dark-coloured warts or swellings that are scattered 

irregularly over the surface of Peltigera (Peltidea) aphthosa. This lichen has 

a grey foliose thallus of rather large sparingly divided lobes; it spreads 

about a hand-breadth or more over the surface of the ground in moist upland 

localities. The specific name " aphthosa " was given by Linnaeus to 

1 Riddle 1910.

i 3 8 MORPHOLOGY 

the plant on account of the supposed resemblance of the dotted thallus to 

the infantile ailment of " thrush." Babikoff l has published an account of 

the formation and development of these Peltidea cephalodia. He determined 

the algae contained in them to be Nostoc by isolating and growing them on 

moist sterilized soil. He observed that the smaller, and presumably younger, 

excrescences were near the edges of the lobes. The cortical cells in that 

position grow out into fine septate hairs that are really the ends of growing 

hyphae. Among the hairs were scattered minute colonies of Nostoc cells 

lying loose or so closely adhering to the hairs as to be undetachable (Fig. 

78 A). In older stages the hairs, evidently 

stimulated by contact with the 

Nostoc, had increased in size and sent 

out branches, some of which penetrated 

the gelatinous algal colony; others, 

spreading over its surface, gradually 

formed a cortex continuous with that 

of the thallus. The alga also increased, 

and the structure assumed a rounded or 

lentiform shape. The thalline cortex 

immediately below broke down, and 

Fig. 78 

the underlying gonidial zone almost 

A. Hairs of Peltigera aphthosaVIi\\&. 

associated with Nostoc colony much mag- 

7 S S 

wholly died off and became absorbed. 

nified (after Babikoff). The hyphae of the cephalodium had 

meanwhile penetrated downwards as root-like filaments, those of the thallus 

growing upwards into the new overlying tissue (Fig. 78 B). The foreign 

alga has been described as parasitic, as it draws from the lichen hyphae the 

necessary inorganic food material; but it might equally well be considered 

as a captive pressed into the service of the lichen to aid in the work of assi- 

milation or as a willing associate giving and receiving mutual benefit. 

Th. M. Fries 2 had previously described the development of the cephalodia 

in Stereocaulon but failed to find the earliest stages. He concluded from his 

observations that parasitic algae were common in the cortical layer of the 

lichens, but only rarely formed the " monstrous growths " called cephalodia. 

b. ENDOTROPHIC. Winter 3 examined the later stages of internal cephalodine 

formation in a species of Sticta. The alga, probably a species of 

Rivularia, which gives origin to the cephalodia, may be situated immediately 

below the upper cortex, in the medullary layer close to the gonidial zone, 

or between the pith and the under cortex. The protuberance caused by the 

increasing tissue, which also contains the invading alga, arises accordingly 

either on the upper or the lower surface. In some cases it was found that 

the normal gonidial layer had been pushed up by the protruding cephalodium 

1 Babikoff 1878. 

2 Th. M. Fries 1866. 3 Winter 1877.


and lay like a cap over the top. The cephalodia described by Winter are 

endogenous in origin, though the mature body finally emerges 

from the 

interior and becomes either epigenous or hypogenous. Schneider 1 has fol- 

lowed the development of a somewhat similar endotrophic or endogenous type 

Fig. 788. Peltigera aphthosa Willd. Vertical section of thai lus and 

cephalodium x 480 (after Babikoff). 

in Sticta oregana due also to the presence of a species of Rivularia. How 

the alga attained its position in the medulla of the thallus was not observed. 

Both the algal cells of internal cephalodia and the hyphae in contact 

with them increase vigorously, and the newly formed tissue curving upwards 

or downwards appears on the outside as a swelling or nodule varying in 

size from that of a pin-head to a pea. On the upper surface the gonidial 

zone partly encroaches on the nodule, but the foreign alga remains in the 

centre of the structure well separated from the thalline gonidia by a layer 

of hyphae. The group is internally divided into small nests of dark-green 

algae surrounded by strands of hyphae (Fig. 79). The swellings, when they 

Fig. 79. Nephroma expallidum Nyl. Vertical section 

of thallus. a, endotrophic cephalodium x 100 (after 

Forssell). 

1 Schneider 1807.

1 40 

MORPHOLOGY 

occur on the lower surface of the lichen, correspond to those of the upper 

in general structure, but there is no intermixture of thalline gonidia. That 

Nostoc cells can grow and retain the power to form chlorophyll in adverse 

conditions was proved by Etard and Bouilhac 1 who made a culture of the 

alga on artificial media in the dark, when there was formed a green pigment 

of chlorophyll nature. 

Endotrophic cephalodia occur in many groups of lichens' Hue 2 states 

that he found them in twelve species of Aspicilia. As packets of blue-green 

algae they are a constant feature in the thallus of Solorinae. The species of 

that genus grow on mossy soil in damp places, and must come frequently 

in contact with Nostoc colonies. In Solorina crocea an interrupted band of 

blue-green algae lies below the normal gonidial zone and sometimes replaces 

it a connecting structure between cephalodia and a true gonidial zone. 

c. PSEUDOCEPHALODIA. Under this section have been classified those 

cephalodia that are almost independent of the lichen thallus though to some 

extent organically connected with it, as for instance that of Lecidea panaeola 

which originate on the hypothallus of the lichen and maintain their position 

between the crustaceous granules. 

The cephalodia of Lecanora gelida, as described by Sernander 3 

, might 

also be included here. He watched their development in their native habitat, 

an exposed rock-surface which was richly covered with the lichen in all 

stages of growth. Two kinds of thallus, the one containing blue-green algae 

(Chroococcus}, the other bright-green, were observed on the rock in close 

proximity. At the point of contact, growth ceased, but the thallus with 

bright-green algae, being the more vigorous, was able to spread round and 

underneath the other and so gradually to transform it to a superficial flat 

cephalodium. All such thalli encountered by the dominant lichen were 

successively surrounded in the same way. The cephalodium, growing more 

slowly, sent root-like hyphae into the tissue of the underlying lichen, and 

the two organisms thus became organically connected. Sernander considers 

that the two algae are antagonistic to each other, but that the hyphae can 

combine with either. 

The pseudocephalodia of Usnea species are abortive apothecia; they are 

surrounded at the base by the gonidial zone and cortex of the thallus, and 

they contain no foreign gonidia. 

E. AUTOSYMBIOTIC CEPHALODIA 

Bitter 4 has thus designated small scales, like miniature thalli, that develop 

constantly on the upper cortex of Peltigera lepidophora, a small lichen not 

uncommon in Finland, and first recorded by Wainio as a variety of Peltigera 

1 Etard and Bouilhac 1898. 

2 Hue I9 , o 3 Sernander 1907. 

* Bitter 1904.


canina. The alga contained in the scales is a blue-green Nostoc similar to 

the gonidia of the thallus. Bitter 1 described the development as similar to 

that of the cephalodia of Peltigera aphthosa, but the outgrowths, being lobate 

in form, are less firmly attached and thus easily become separated and dis- 

persed ; as the gonidia are identical with those of the parent thallus they 

act as vegetative organs of reproduction. 

Bitter's work has been criticized by Linkola 2 who claims to have dis- 

covered by means of very thin microtome sections that there is a genetic 

connection between the scales and the underlying thallus, not only with the 

hyphae, as in true cephalodia, but with the algae as well, so that these outgrowths 

should be regarded as isidia. 

In the earliest stages, according to Linkola, a small group of algae may 

be observed in the cortical tissue of the Peltigera apart from the gonidial 

zone and near the upper surface. Gradually a protruding head is formed 

which is at first covered over with a brown cortical layer one cell thick. The 

head increases and becomes more lobate in form, being attached to the thallus 

at the base by a very narrow neck and more loosely at other parts of the 

scale. In older scales, the gonidia are entirely separated from those of the 

thallus, and a dark-brown cortex several cells in thickness covers over the 

top and sides; there is a colourless layer of plectenchyma beneath. At this 

advanced stage the scales are almost completely superficial and correspond 

with the cephaloidal rather than with the isidial type of formation. The 

algae even in the very early stages are distinct from the gonidial zone and 

the whole if development, isidial, must be considered as somewhat abnormal. 

3. 

SOREDIA 

A. STRUCTURE AND ORIGIN OF SOREDIA 

Soredia are minute separable parts of the lichen thallus, and are com- 

posed of one or more gonidia which are clasped and surrounded by the 

lichen hyphae (Fig. 80). They occur on the sur- 

face or margins of the thallus of a fairly large 

number of lichens either in a powdery excrescence 

or in a pustule-like body comprehensively termed 

a "soralium" (Fig. 81). The soralia vary in form Fig. 80. Soredia. a, of Phystia 

and dimensions according to the species. Each fuiveruitntaXyl.-b, tiRamahnafartnacea 

Ach. x 600. 

individual soredium is capable of developing into 

a new plant; it is a form of vegetative reproduction characteristic of lichens. 

Acharius 3 

gave the name " soredia " to the powdery bodies with reference 

to their propagating function; he also interpreted the soredium as an "apothecium 

of the second order." But long before his time they had been 


2 Linkola 1913. 

3 

Acharius, 1798, p. xix, and 1810, pp. 8 and 10.

I4 2 

MORPHOLOGY 

observed and commented on by succeeding botanists: first by Malpighi 1 

who judged them to be seeds, he having seen them develop new plants; by 

Fig. 81. Vertical section of young soralium of Evernia Jurfuracea 

var. soralifera Bitter x 60 (after Bitter). 

Micheli 2 who however distinguished between the true fruit and those seeds; 

and by Linnaeus 3 who considered them to be the female organs of the 

plant, the apothecia being, as he then thought, the male organs. Hedwig 4 

on the other hand, regarded the apothecia as the seed receptacles 

and the 

soredia as male bodies. Sprengel's 5 statement that they were "a subtile 

germinating powder mixed with delicate hair-like threads which take the 

place of seeds" established 6 

finally their true function. Wallroth who was 

, 

the first really to investigate their structure and their relation to the parent 

plant, recognized them as of the same type as the "brood-cells" or gonidia; 

and as the latter, he found, could become free from the thallus and form a 

green layer on trees, walls, etc., in shady situations, so the soredia also 

could become free, though for a time they remained attached to the lichen 

and were covered by a veil, i.e. by the surrounding hyphal filaments. Koerber 

7 also gave much careful study to soredia, their nature and function. As 

propagating organs he found they were of more importance than spores, 

especially in the larger lichens. 

According 

to Schwendener 8 

, the formation of soredia is due to increased 

and almost abnormal activity of division in the gonidial cell; the hyphal 

filament attached to it also becomes active and sends out branches from the 

cell immediately below the point of contact which force their way between 

the newly divided gonidia and finally surround them. A soredial "head" 

1 

Malpighi, 1686, p. 50, pi. 27, fig. 106. 

2 

Micheli 1729, pp. 73, 74. 

3 Linnaeus 1737, p. 325. 

4 

Hedwig 1798. 

6 

Sprengel 1807, Letter xxili. 


6 Wallroth 1825, I. p. 595. 

7 Koerber 1841. 

,

STRUCTURES PECULIAR TO LICHENS 

of smaller or larger size is thus gradually built up on the stalk filament or 

filaments, and is ultimately detached by the breaking down of the slender 

support. 

a. SCATTERED SOREDIA. The simplest example of soredial formation 

may be seen on the bark of trees or on palings when the green coating of 

algal cells is gradually assuming a greyish hue caused by the invasion of 

hyphal lichenoid growth. This condition is " 

generally referred to as leprose " 

and has even been classified as a distinct genus, Lepra or Lepraria. 

Somewhat similar soredial growth is also associated with many species of 

Cladonia, the turfy soil in the neighbourhood of the upright podetia being 

often powdered with white granules. Such soredia are especially abundant 

in that genus, so much so, that Meyer 1 Krabbe , 2 and others have maintained 

that the spores take little part in the propagation of species. The under 

side of the primary thallus, but more frequently the upright podetia, are 

often covered with a coating of soredia, either finely furfuraceous, or of larger 

growth and coarsely granular, the size of the soredia depending on the 

number of gonidia enclosed in each " head." 

Soredia are only occasionally present on the apothecial margins: the 

rather swollen rims in Lobaria scrobiculata are sometimes powdery-grey, and 

Bitter 3 has observed soredia, or rather soralia, on the apothecial margins of 

Parmelia vittata; they are very rare, however, and are probably to be ex- 

plained by excess of moisture in the surroundings. 

b. ISIDIAL SOREDIA. In a few lichens soredia arise by the breaking 

down of the cortex at the tips of the thalline outgrowths termed "isidia." 

In Parmelia verruculifera, for instance, where the coralloid isidia grow in 

closely packed groups or warts, the upper part of the isidium frequently 

becomes soredial. In that lichen the younger parts of the upper cortex 

bear hairs or trichomes, and the individual soredia are also adorned with 

hairs. The somewhat short warted 

isidia of P. subaurifera may become 

entirely sorediose, and in P.farinacea 

the whole thallus is covered with isidia 

transformed into soralia. The trans- 

formation is constant and is a distinct 

specific character. Bitter 3 considers 

that it proves that no sharp distinction 

exists between isidia and soralia, at 

least in their initial stages. 

c. SOREDIA AS BUDS. Schwen- 

dener 4 has described soredia in the 

1 

Meyer 1825, p. 170. 

2 Krabbe 1891.. 

Fig. 82. Usttea barbata Web. Longitudinal 

section of filament and base of "soredial" 

branch x 40 (after Schwendener). 

Bitter 1901. 

4 Schwendener 1860, p. 137.

i 44 

MORPHOLOGY 

genus Usnea which give rise to new branches. Many of the species in that 

genus are plentifully sprinkled with the white powdery bodies. A short 

way back from the apex of the filament the separate soredia show a tendency 

to apical growth and might be regarded as groups of young plants still 

attached to the parent branch. One of these developing more quickly 

pushes the others aside and by continued growth fills up the soredial 

opening in the cortex with a plug of tissue; finally it forms a complete 

lateral branch. Schwendener calls them "soredial" branches (Fig. 82) to 

distinguish 

development. 

them from the others formed in the course of the normal 

B. SORALIA 

In lichens of foliose and fruticose structure, and in a few crustaceous 

forms, the soredia are massed together into the compact bodies called soralia, 

and thus are confined to certain areas of the plant surface. The simpler 

soralia arise from the gonidial zone below the cortex by the active division 

of some of the algal cells. The hyphae, interlaced with the green cells, are 

thin-walled and are, as stated by Wainio 1 

, still in a meristematic condition ; 

they are thus able readily to branch and to form new filaments which clasp 

the continually multiplying gonidia. This growth is in an upward or outward 

direction away from the medulla, and strong mechanical pressure is 

exerted by the increasing tissue on the overlying cortical layers. Finally 

the soredia force their way through to the surface at definite points. The 

cortex is thrown back and forms a margin round the soralium, though shreds 

of epidermal tissue remain for a time mixed with the powdery granules. 

a. FORM AND OCCURRENCE OF SORALIA. The term " soralium " was 

first applied only to the highly developed soredial structures considered by 

Acharius to be secondary apothecia; it is now employed for any circum- 

scribed group of soredia. The soralia vary in size and form and in position, 

according to the species on which they occur; these characters are constant 

enough to be of considerable diagnostic value. Within the single genus 

Parmelia, they are to be found as small round dots sprinkled over the 

surface of P. dubia; as elongate furrows irregularly placed on P. sulcata; as 

pearly excrescences at or near the margins of P. perlata, and as swollen 

tubercles at the tips of the lobes of P.physodes (Fig. 83). Their development 

is strongly influenced and furthered by shade and moisture, and, given such 

conditions in excess, they may coalesce and cover large patches of the thallus 

with a powdery coating, though only in those species that would have borne 

soredia in fairly normal conditions. 

Soralia of definite form are of rather rare occurrence in crustaceous lichens, 

1 Wainio 1897, p. 32. 

2 Reinke 1895, p. 380.


with the exception of the Pertusariaceae, where they are frequent, and some 

species of Lecanora and Placodium. They are known in only two hypo- 

Fig. 83. Parmelia physodes Ach. Thallus growing horizontally ; soredia on 

the ends of the lobes (S. H. , Photo.}. 

Xylographa spilomatica. 

Among squamulose thalli they are typical of some Cladoniae, and also of 

Lecidea (Psora) ostreata, where they are produced on the upper surface to- 

wards the apex of the squamule. 

b. POSITION OF SORALIFEROUS LOBES. According to observations'made 

1 

by Bitter the occurrence of soralia on one lobe or another , 

may depend to 

a considerable extent on the orientation of the thallus. He cites the varia- 

bility in habit of the familiar lichen, Parmelia physodes and its various forms, 

which grow on trees or on soil. In the horizontal thalli there is much less 

tendency to soredial formation, and the soredia that arise are generally 

confined to branching lobes on the older parts of the thallus. 

That type of growth is in marked contrast with the thallus obliged to 

take a vertical direction as on a tree. In such a case the lobes, growing 

downward from the point of origin, form soralia at their tips at an early 

stage (Fig. 84). The lateral lobes, and especially those that lie close to the 

substratum, are the next to become soraliate. Similar observations have 

been made on the soraliferous lobes of Cetraria pinastri. The cause is 

probably due to the greater excess of moisture draining downwards to the 

lower parts of the thallus. The lobes that bear the soralia are generally 

1 

Bitter : 

9or.

1 46 MORPHOLOGY 

narrower than the others and are very frequently raised from contact with 

the substratum. They tend to grow out from the thallus in an upright 

Fig. 84. Parmelia physodes Ach. Thallus growing vertically 

; soredia chiefly on the lobes directed downwards, 

reduced (M. P., Photo.'). 

direction and then to turn backwards at the tip, so that the opening of the 

soralium is directed downwards. Bitter says that the cause of this change 

in ^direction is not clear, though possibly on teleological reasoning it is of 

from direct 

advantage that the opening of the soralium should be protected 

rainfall. The opening lies midway between the upper and lower cortex, and 

the upper tissue in these capitate soralia continues to grow and to form an 

arched helmet or hood-covering which serves further to protect the soralium. 

Similar soralia are characteristic of Physcia Jiispida (Ph. stellaris subsp. 

tenella\ the apical helmet being a specially pronounced feature of that species, 

though, as Lesdain 1 has pointed out, the hooded structures are primarily 

the work of insects. In vertical substrata they occur on the lower lobes of 

the plant. 

Apical soralia are rare in fruticose lichens, but in an Alpine variety of 

1 Lesdain 1910.


Ramalina minusctila they are formed at the tips of the fronds and are protected 

by an extension of the upper cortical tissues. Another instance occurs 

in a Ramalina from New Granada referred by Nylander to R. calicaris var. 

farinacea: it presents a striking example of the helmet tip. 

c. DEEP-SEATED SORALIA. In the cases already described Schwendener 1 

and Nilson 2 held that the algae gave the first impulse to the formation of 

the soredia; but in the Pertusariaceae 3 

, 

a family of crustaceous lichens, there 

has been evolved a type of endogenous soralium which originates with the 

medullary hyphae. In these, special hyphae rise from a weft of filaments 

situated just above the lowest layer of the thallus at the base of the medulla, 

the weft being distinguished from the surrounding tissue by staining blue 

with iodine. A loose strand of hyphae staining the usual yellow colour rises 

from the surface of the "blue" weft and, traversing the medullary tissue, 

surrounds the gonidia on the under side of the gonidial zone. The hyphae 

continue to' grow upward, pushing aside both the upper gonidial zone and 

the cortex, and carrying with them the algal cells first encountered. When 

the summit is reached, there follows a very active growth of both gonidia 

and hyphae. Each separate soredium so produced consists finally of five to 

ten algal cells surrounded by hyphae and measures 8/i to 13/14 in diameter. 

The cortex forms a well-defined wall or margin round the mass of soredia. 

A slightly different development is found in Lecanora tartarea, one of 

the "crottle" lichens, which has been placed by Darbishire in Pertu- 

sariaceae. The hyphae destined to form soredia also start from the weft of 

tissue at the base of the thallus, but they simply grow through the gonidial 

zone instead of pushing it aside. 

In his examination of Pertusariaceae Darbishire found that the apothecia 

also originated from a similar deeply seated blue-staining tissue, and he con- 

cluded that the soralia represented abortive apothecia and really corresponded 

to Acharius's "apothecia of the second order." His conclusion as to the 

4 

Bitter who considers that 

homology of these two organs is disputed by , 

the common point of origin is explained by the equal demand of the hyphae 

in both cases for special nutrition, and by the need of mechanical support 

at the base to enable the hyphae to reach the surface and to thrust back the 

cortex without deviating from their upward course through the tissues. 

C. DISPERSAL AND GERMINATION OF SOREDIA 

Soredia become free by the breaking down of the hyphal stalks at the 

septa or otherwise. They are widely dispersed by wind or water and soon 

make their appearance on any suitable exposed soil. Krabbe 5 has stated 


2 

Nilson 3 

1903. 

Darbishire 1897. 


4 Bitter 1901, p. 191.

148 

MORPHOLOGY 

that, in many cases,- the loosely attached soredia coating some of the 

Cladonia podetia are of external origin, carried thither by the air-currents. 

Insects too aid in the work of dissemination: Darbishire 1 has told us how 

he watched small mites and other insects moving about over the soralia of 

Pertusaria amara and becoming completely powdered by the white granules. 

Darbishire 1 also gives an account of his experiments in the culture of 

soredia. He sowed them on poplar wood about the beginning of February 

in suitable conditions of moisture, etc. Long hyphal threads were at once 

produced from the filaments surrounding the gonidia, and gonidia that had 

become free were seen to divide repeatedly. Towards the end of August of 

the same year a few soredia had increased in size to about 450/11, in diameter, 

and were transferred to elm bark. By September they had further increased 

to a diameter of 520/1-, and the gonidia showed a tendency towards aggregation. 

No further differentiation or growth was noted. 

More success attended Tobler's 2 

to cultivate the soredia of 

attempt 

Cladonia sp. He sowed them on soil kept suitably moist in a pot and after 

about nine months he obtained fully formed squamules, at first only an iso- 

lated one or two, but later a plentiful crop all over the surface of the soil. 

Tobler also adds that soredia taken from a Cladonia, that had been kept for 

about half a year in a dry room, grew when sown on a damp substratum. 

The algae however had suffered more or less from the prolonged desiccation, 

and some of them failed to develop. 

A suggestion has been made by Bitter 3 that a hybrid plant might result 

from the intermingling of soredia from the thallus of allied lichens. He 

proposed the theory to explain the great similarity between plants of Par- 

melia physodes and P. tubulosa growing in close proximity. There is no 

proof that such mingling of the fungal elements ever takes place. 

D. EVOLUTION OF SOREDIA 

Soredia have been compared to the gemmae of the Bryophytes and also 

to the slips and cuttings of the higher plants. There is a certain analogy 

between all forms of vegetative reproduction, but soredia are peculiar in 

that they include two dissimilar organisms. In the lichen kingdom there 

has been evolved this new form of propagation in order to secure the con- 

tinuance of the composite life, and, in a number of species, it has almost 

entirely superseded the somewhat uncertain method of spore germination 

inherited from the fungal ancestor, but which leaves more or less to chance 

the encounter with the algal symbiont. 

From a phylogenetic point of view we should regard the sorediate lichens 

as the more highly evolved, and those which have no soredia as phylo- 


2 Tobler 191 1 2 , n. 3 Bitter ipoi 2 .


genetically young, though, as Lindau 1 has pointed out, soredia are all com- 

paratively recent. They probably did not appear until lichens had reached 

a more or less advanced stage of development, and, considering the poly- 

phyletic origin of lichens, they must have arisen at more than one point, 

and probably at first in circumstances where the formation of apothecia was 

hindered by prolonged conditions of shade and moisture. 

That soredia are ontogenetic in character, and not, as Nilson 2 has asserted, 

accidental products of excessively moist conditions is further proved by the 

non-sorediate character of those species oforustaceous lichens belonging to 

Lecanora, Verrucaria, etc. that are frequently immersed in water. Bitter 3 

found that the soredia occurring on Peltigera spuria were not formed on the 

lobes which were more constantly moist, nor at the edges where the cortex 

was thinnest: they always emerged on young parts of the thallus a short 

way back from the edge. 

Bitter 3 

points out that in extremely unfavourable circumstances in the 

polluted atmosphere near towns, or in persistent shade lichens, that would 

otherwise form a normal thallus, remain in a backward sorediose state. He 

considers, however, that many of these formless crusts are autonomous growths 

with specific morphological and chemical peculiarities. They hold these 

outposts of lichen vegetation and are not found growing in any other localities. 

The proof would be to 

watch development. 

transport them to more favourable conditions, and 

4. ISIDIA 

A. FORM AND STRUCTURE OF ISIDIA 

Many lichens are rough and scabrous on the surface, with minute simple 

or divided coral-like outgrowths of the same texture as the underlying thallus, 

though sometimes they are darker in colour as in Evernia furfuracea. They 

always contain gonidia and are covered by a cortex continuous with that 

of the thallus. 

This very marked condition was considered by Acharius 4 as of generic 

importance and the genus, Isidium, was established byhim, with the diagnostic 

characters: "branchlets produced on the surface, or coralloid, simple and 

branched." In the genus were included the more densely isidioid states of 

various crustaceous species such as Isidium corallinum and /. Westringii, 

both of which are varieties of Pertusariae. Fries 5 

, with his accustomed insight, 

recognized them as only growth forms. The genus was however still accepted 

in English Floras 6 as late as 1833, though we find it dropped by Taylor 7 in 

the Flora Hibernica a few years later. 


5 Fries 1825. 

2 Nilson 1903. 

6 Hooker 1833. 


7 Taylor 1836. 

4 Acharius 1798, pp. 2, 87.

MORPHOLOGY 

The development of the isidial outgrowth has been described by Rosen- 

dahl 1 in several species of Parmelia. In one of them, P. papulosa, which has 

a cortical layer one cell thick, the isidium begins as a small swelling or wart 

on the upper surface of the thallus. At that stage the cells of the cortex 

have already lost their normal arrangement and show irregular division. 

They divide still further, as gonidia and hyphae push their way up. The 

full-grown isidia in this species are cylindrical or clavate, simple or branched. 

They are peculiar in that they bear laterally 

here and there minute rhizoids, a development 

not recorded in any other isidia. The inner 

tissue accords with that of the normal thallus 

and there is a clearly marked cortex, gonidial 

zone and pith. A somewhat analogous development 

takes place in the isidia of Parmelia pro- 

boscidea; in that lichen they are mostly prolonged 

into a dark-coloured cilium. 

In Parmelia scortea the cortex is several 

cells thick, and the outermost rows are com- 

pressed and dead in the older parts of the 

thallus; but here also the first appearance of 

the isidium is in the form of a minute wart. 

The lower layers (4 to 6) of living cortical cells 

divide actively; the gonidia also share in the 

new growth, and the protuberance thus formed 

pushes off the outer dead cortex and Fig. 85. Vertical section of isidia of 

Parmelia scortea Ach. A, early 

: 

stage; 60 (after 

emerges 

as an isidium (Fig. 85). They are always rather 

stouter in form than those of P. papulosa and 

B. later stage, 

Rosendahl). 

may be simple or branched. The gonidia in this case do not form a 

definite zone, but are scattered through the pith of the isidium. 

Here also should be included the coralloid branching isidia that adorn 

the upper surface and margins of the thallus of Umbilicaria pusttilata. 

They begin as small tufts of somewhat cylindrical bodies, but they sometimes 

broaden out to almost leafy expansions with crisp edges. Most 

frequently they are situated on the bulging pustules where intercalary 

growth is active. Owing to their continued development on these areas, 

the tissue becomes slack, and the centre of the isidial tuft may fall out, 

leaving a hole in the thallus which becomes still more open by the tension 

of thalline expansion. New isidia sprout from the edges of the wound and 

the process may again be repeated. It has been asserted that these structures 

are only formed on injured parts of the thallus something like gallformations 

but Bitter 2 has proved that the wound is first occasioned by 

the isidial growth weakening the thallus. 


2 Bitter 1899.


B. ORIGIN AND FUNCTION OF ISIDIA 

Nilson 1 

(later Kajanus 2 

) insists that isidia and soredia are both products 

of excessive moisture. He argues that lichen species, in the course of their 

development, have become adapted to a certain degree of humidity, and, if 

the optimum is passed, the new conditions entail a change in the growth 

of the plant. The gonidia are stimulated to increased growth, and the 

mechanical pressure exerted by the multiplying cells either results in the 

emergence of isidial structures where the cortex is unbroken, or, if the 

cortex is weaker and easily bursts, in the formation of soralia. 

This view can hardly be accepted ; isidia as well as soredia are typical 

of certain species and are produced regularly and normally in ordinary 

conditions; both of them are often present on the same thallus. It is not 

denied, however, that their development in certain instances is furthered 

by increased shade or moisture. In Evernia furfuracea isidia are more 

freely produced on the older more shaded parts of the thallus. Zopf 3 has 

described such an instance in Evernia olivetorina (E. furfuracea)^ which 

grew in the high Alps on pine trees, and which was much more isidiose 

when it grew on the outer ends of the branches, where dew, rain or snow 

had more direct influence. He 4 

in forms 

quotes other examples occurring 

of E. furfuracea which grew on the branches of pines, larches, etc. in a damp 

locality in S. Tyrol. The thalli hung in great abundance on each side of 

the branches, and were invariably more isidiose near the tips, because 

evidently the water or snow trickled down and was retained longer there 

than at the base. 

Bitter 5 has given a striking instance of shade influence in Umbilicaria. 

He found that some boulders on which the lichen grew freely had become 

covered over with fallen pine needles. The result was at first an enormous 

increase of the coralline isidia, though finally the lichen was killed by the 

want of light. 

Isidia are primarily of service to the plant in increasing the assimilating 

surface. Occasionally they grow out into new thallus lobes. The more 

slender are easily rubbed off, and, when scattered, become efficient organs 

of propagation. This view of their function is emphasized by Bitter who 

points out that both in Evernia furfuracea and in Umbilicaria pustulata 

other organs of reproduction are rare or absent. Zopf 3 found new plants 

of Evernia furfuracea beginning to grow on the trunk of a tree lower 

down than an old isidiose specimen. They had developed from isidia which 

had been detached and washed down by rain. 

1 Nilson 1903. 

a Kajanus (Nilson) 1911. 


3 

Zopf 1903. 

4 

Zopf 19052.

1 52 

MORPHOLOGY 

VI. HYMENOLICHENS 

A. SUPPOSED AFFINITY WITH OTHER PLANTS 

Lichens in which the fungal elements belong to the Hymenomycetes 

are confined to three tropical genera. They are associated with blue-green 

algae and are most nearly related to the Thelephoraceae among fungi. The 

spores are borne, as in that family, on basidia. 

The best known Hymenolichen, Cora Pavonia (Fig. 86), was discovered 

during his travels in the W. Indies (1785-87) growing on trees 

by Swartz 1 

Fig. 86. Cora Pavonia Fr. (after Mattirolo). 

in the mountains of Jamaica, and the new plant was recorded by him as 

Ulva montana. Gmelin 2 also included it in Ulva in close association with 

Ulva (Padind) Pavonia, but that classification was shortly after disputed by 

Woodward 3 who thought its affinity was more nearly with the fungi and 

near to Boletus 

suggested that it should be made the type of a new genus 

(Polystictus} versicolor. 

4 

Fries in due time made the new genus Cora, though 

he included it among algae; finally N.ylander 5 established the lichenoid 

character of the thallus and transferred it to the Lecanorei. 

It was made the subject of more exact investigation by Mattirolo 6 who 

1 Swartz 1788. 

2 Gmelin 1791. 


3 Woodward 1797. 

6 

Mattirolo 1881. 

4 Fries 1825.

HYMENOLICHENS 153 

recognized its affinity with Thelephora, a genus of Hymenomycetes. Later 

Johow 1 went to the West Indies and studied the Hymenolichens in their 

native home. The genera and species described by Johow have been 

reduced to Cora and Dictyonema ; 

by Wainio 2 . 

a new genus Corella has since been added 

Johow found that Cora grew on the mountains usually from 1000 to 

2000 ft. above sea-level. As it requires for its 

development a cool damp climate with strong 

though indirect illumination, 

neither 1 

it is found 

in sunny situations nor in the depths 

of dark woods. It grows most freely in diffuse 

light, on the lower trunks and branches of 

trees in open situations, but high up on the 

stem where the vegetation is more dense. 

It stands out from the tree like a small thin 

bracket fungus, one specimen placed above 

another, with a dimidiate growth similar to 

that of Polystictus versicolor. Both surfaces 

are marked by concentric zones which give 

it an appearance somewhat like Padina Pa- 

vonia. These zones indicate unequal intercalary 

growth both above and below. The 

whole plant is blue-green when wet, greyishwhite 

when dry, and of a thin membranaceous 

consistency. 

B. STRUCTURE OF THALLUS 

There is no proper cortex in any of the 

genera, but in Cora there is a fastigiate 

branching of the hyphae in parallel lines 

towards the upper surface; just at the outside 

they turn and lie in a horizontal direction, 

and, as the branching becomes more profuse, 

a rather compact cover is formed. The gonidia, 

which consist of blue-green Chroococcus 

cells, lie at the base of the upward branches 

and they are surrounded with thin-walled short-celled hyphae closely interwoven 

into a kind of cellular tissue. The medulla of loose hyphae passes 

over to the lower cortex, also of more or less loose filaments. The outermost 

cells of the latter very frequently grow out into short jagged or crenate 

processes (Fig. 87). 

1 

Johow 1884. 

Fig. 87. Cora Pavonia Fr. Vertical 

section of thallus. a, upper cortex ; 

b, gonidial layer; t, medulla and 

lower cortex of crenate cells; d, tuft 

of fertile hyphae. x 160. e, basidia 

and spores x 1000 (after Johow). 

2 Wainio 1890.

154 

MORPHOLOGY 

In Corella, the mature lichen is squamulose or consists of small lobes; in 

Dictyonema there is a rather flat dimidiate expansion; in both the alga is 

Scyt0nema,thetrichomes of which largely retain their form and are surrounded 

by parallel growths of branching hyphae. The whole tissue is loose and 

spongy. 

Corella spreads over soil on a white hypothallus without rhizinae. In 

the other two genera which live on soil, or more frequently on trees, there 

is a rather extensive formation of hold-fast tissue. When the dimidiate 

thallus grows on a rough bark, rhizoidal strands of hyphae travel over it 

and penetrate between the cracks; if the bark is smooth, there is a more 

continuous weft of hyphae. In both cases a spongy cushion of filamentous 

tissue develops at the base of the lichen between the tree and the bracket 

thallus. There is also in both genera an encrusting form which Johow 

regarded as representing a distinct genus Laudatea, but which Moller found 

to be merely a growth stage. Moller 1 

judged from that and from other 

characteristics that the same fungus enters into the composition of both 

Cora and Dictyonema and that only the algal constituents are different. 

C. SPORIFEROUS TISSUES 

As in Hymenomycetes, the spores of Hymenolichens are exogenous, 

and are borne at the tips of basidia which in these lichens are produced on 

the under surface of the thallus. In Cora the fertile filaments may form a 

continuous series of basidia over the surface, but generally they grow out 

in separate though crowded tufts. As these tufts broaden outwards, they 

tend to unite at the free edges, and may finally present a continuous 

hymenial layer. Each basidium bears four sterigmata and spores (Fig. 87 e}\ 

paraphyses exactly similar to the basidia are abundant in the hymenium. 

In Dictyonema the hymenium is less regular, but otherwise it resembles that 

of Cora. No hymenium has as yet been observed in Corella; it includes, so 

far as known, one species, C. brasiliensis , which spreads over soil or rocks. 

1 Moller 1893.

CHAPTER IV 

REPRODUCTION 

I. REPRODUCTION BY ASCOSPORES 

A. HISTORICAL SURVEY 

THE earliest observations as to the propagation of lichens were made by 

Malpighi 1 who recorded the presence of soredia on the lichen plant and 

noted their function as reproductive bodies. He was followed after a con- 

siderable interval by Tournefort 2 who placed lichens in a class apart owing 

to the form of the fruit: "This fruit," he writes, "is a species of bason or 

cup which seems to take the place of seeds in these kinds of plants." He 

figures Ramalinafraxinea and Physcia ciliaris, both well fruited specimens, 

and he represents the " minute dust " contained in the fruits as subrotund 

in form. The spores of Physcia ciliaris are of a large size and dark in colour 

and were undoubtedly seen by Tournefort. Morison 3 

, in his History of 

Oxford Plants, published very shortly after, dismissed Tournefort's "seeds" 

as being too minute to be of any practical interest. 

Micheli 4 

, with truer scientific insight, made the fruiting organs the subject 

of special study. He decided that the apothecia were floral receptacles, 

receptacula florum, and that the spores were the " flowers " of the lichen. He 

has figured them in a vertical series in situ, in a section of the disc of Solorina 

saccata 6 and also in a species of Pertusaria 5 

, in both of which plants the 

ascospores are unusually large. 

" 

semina." 

He adds that he had not so far seen the 

Micheli's views were not shared by his immediate successors. Dillenius 6 

scarcely believed that the spores could be " flowers " 

and, in any case, he 

concluded that they were too minute to be of any real significance in the 

life of the plant. 

Linnaeus 7 and after him Necker , 

8 

, Scopoli 9 and others describe the apothecia 

as the male, the soredia as the female organs of lichens. These old 

time botanists worked with very low powers of magnification, and easily went 

astray in the interpretation of imperfectly seen phenomena. 

Koelreuter 10 

, a Professor of Natural History in Carlsruhe, who pub- 

lished a work on The discovered Secret of Cryptogams, next hazarded the 

opinion that the seeds of lichens originated from the substance of the pith, 

and that the overlying cortical layer supplied the fertilizing sap. Hoffmann 11 

1 

Malpighi 1686. 

3 Micheli, Pis. 52 and 56. 

" 

Scopoli 1772. 


B Dillenius 1741. 

10 Koelreuter 1777. 

3 4 Morison 1699. Micheli 1729. 

7 8 

Linnaeus 1737. Necker 1771, p. 257. 

u Hoffmann 1784.

156 

REPRODUCTION 

devoted a great deal of attention to lichen fructification and he also thought 

that fertilization must take place within the tissue of the lichens. He 

regarded the soredia as the true seeds, while allowing that a second series 

of seeds might be contained in the scutellae (apothecia). 

A distinct advance was made by Hedwig 1 

, a Professor of Botany in 

Leipzig, towards the end of the eighteenth century. He followed Tourne- 

fort in selecting Physcia ciliaris for research, and in that plant he describes 

and figures not only the apothecia with the dark-coloured septate spores, 

but also the pycnidia or spermogonia which he regarded as male organs. 

The soredia, typically represented and figured by him on Parmelia physodes, 

he judged to be " male flowers of a different type." 

Acharius 2 did not add much to the knowledge of reproduction in lichens, 

though he takes ample note of the various fruiting structures for which he 

invented the terms apothecia, perithecia and soredia. Under still another 

term gongyli he included not only spores, but the spore guttulae as well as 

the gonidia or cells forming the soredia. 

Hornschuch 3 of Greifswald described the propagation of the lower lichens 

as being solely by means of a germinating " 

powder " 

; 

the more highly or- 

ganized forms were provided with receptacles or apothecia containing spores 

which he considered as analogous to flowers rather than to fruits. The im- 

portant contributions to Lichenology of Wallroth 4 and Meyer 5 close this 

period of uncertainty: the former deals almost exclusively with the form 

and character of the vegetative thallus and the function of the " 

reproductive 

gonidia." Meyer, a less prolix writer, very clearly states that the method of 

reproduction is twofold: by spores produced in fruits, or by the germinating 

granules of the soredia. 

B. FORMS OF REPRODUCTIVE ORGANS 

From the time of Tournefort, considerable attention had been given to 

the various forms of scutellae, tuberculae, etc., as characters of diagnostic 

importance. Sprengel 6 

grouped these bodies finally into nine different types 

with appropriate names which have now been mostly superseded by the 

comprehensive terms, apothecia and perithecia. A general classification on 

the lines of fruit development was established by Luyken 7 

, who, following 

Persoon's 8 classification of fungi, and thus recognizing their affinity, summed 

up all known lichens as Gymnocarpeae with open fruits, and Angiocarpeae 

with closed fruits. 

a. APOTHECIA. As in discomycetous fungi, the lichen apothecium is 

in the form of an open concave or convex disc, but generally of rather small 

1 

Hedwig 1784. 

6 

Meyer 1825. 

2 

Acharius 1810. 3 Hornschuch 1821. 4 Wallroth 1825. 

6 

Sprengel 1804. 

? 

Luyken 1809. Persoon 1801.

REPRODUCTIVE ORGANS 157 

size, rarely more than I cm. in diameter (Fig. 88); there is no development 

in lichen fruits equal to the cup-like ascomata of the larger Pezizae. In 

Fig. 88. Lecanora subfusca Ach. A, thallus and apothecia x 3 ; 

B, vertical section of apothecium. a, hymenium; b, hypothecium; 

c, thalline margin or amphithecium ; of, gonidia. 

x 60 (after Reinke). 

most cases the lichen apothecium retains its vitality as a spore-bearing 

organ for a considerable period, sometimes for several years, and it is 

of sterile 

strengthened and protected by one or more external margins 

tissue. Immediately surrounding the fertile disc there is a compact wall of 

interwoven hyphae. In some of the shorter-lived soft fruits, as in Biatora, 

this hyphal margin may be thin, and may gradually be pushed aside as the 

disc develops and becomes convex, but generally it forms a prominent rim 

round the disc and may be tough or even horny, and often hard and car- 

bonaceous. This wall, which is present, to some extent, in nearly all lichens, 

is described as the "proper margin." A second "thalline margin" containing 

gonidia is present in many genera 1 : it is a structure peculiar to the lichen 

apothecium and forms the amphithecium. 

At the base of the apothecium there is a weft of light- or dark-coloured 

and round the sides 

hyphae called the hypothecium> which is continued up 

as the parathecium merging into the "proper margin." It forms the lining 

of a cup-shaped hollow which is filled by the paraphyses, which are upright 

closely packed thread-like hyphae, and by the'spore-containing asci or thecae, 

these together constituting the thecium or hymenium. The paraphyses 

are very numerous as compared with the asci ; they are simple or branched, 

1 See also p. 166.

I 5 8 

REPRODUCTION 

frequently septate, especially towards the apex, and mostly slender, varying in 

width from 1-4/4, though Hue describes paraphyses in Aspicilia atroviolacea 

as 8-12/u, thick. They may be thread-like throughout their length, or they 

may widen towards the tips which are not infrequently coloured. Small 

apical cells are often abstricted and lie loose on the epithecium, giving at 

times a pruinose or powdered character to the disc. In some genera there 

is a profuse branching of the paraphyses to form a dense protective epithecium 

over the surface of the hymenium as in the genus Arthonia. 

The apothecia may be sessile and closely adnate to or even sunk in the 

thallus, or they may be shortly stalked. The thalline margin shares generally 

the characters of the thallus; the disc is mostly of a firm consistency and is 

light or dark in colour according to genus or species ; most frequently it is 

some shade of brown. Marginate apothecia, i.e. those with a thalline margin, 

are often referred to as "lecanorine," that being a distinctive feature of 

the genus Lecanora. In the immarginate series, with a proper margin 

only, the texture may be soft and waxy, termed "biatorine" as in Biatora; 

or hard and carbonaceous as in the genus Lecidea, and is then described as 

"lecideine." 

In the subseries Graphidineae, the apothecium has the form of a very 

flat, roundish or irregular body entirely without 

a margin, called an "ardella" as in Arthonia; 

or more generally it is an elongate narrow 

"lirella," in which the disc is a mere slit 

"> between two dark-coloured proper margins. 

The hypothecium of the lirellae is sometimes 

much reduced and in that case the hymenium 

rests directly on a thin layer above the thalline 

tissue as in Graphis elegans (Fig. 89). 

Lichen fruits require abundant light, and 

plants growing in the shade are mostly sterile. 

B 

Fig. 89. Graphis elegans Ach. A,. 

thallus and lirellae; B, vertical 

Naturally, therefore, the reproductive bodies 

, f , , , .,, 

are lo be found on the best illuminated parts 

section of furrowed lirella. x ca. of the thallus. In crustaceous and in most 

the upper surface, 

foliose forms, 

wherever the light falls 

they are variously situated on 

most directly. In the genera 

Nephromium and Nephromopsis, on the contrary, they arise on the under sur- 

face, though at the extreme margin, but as the fertile lobes eventually turn 

upwards the apothecia as they mature become fully exposed. In shrubby 

or fruticose lichens their position is lateral on the fronds, or more frequently 

at or near the tips. 

b. PERITHECIA. The small closed perithecium is characteristic of the 

Pyrenocarpeae which correspond with the Pyrenomycetes among fungi. It


is partially or entirely immersed in the thallus or in the substratum on 

which the lichen grows, and is either a globose or conical body wholly 

surrounded by a hyphal wall, when it is described 

as "entire" (Fig. 90), or it is somewhat 

hemispherical in form and the outer wall is 

developed only on the upper exposed part: 

a type of perithecium usually designated by 

the term "dimidiate." As the perithecial wall 

gives sufficient protection to the asci, the 

paraphyses are of less importance and are 

frequently very sparingly produced, or they 

may even be dissolved and used up at an early 

stage. The thallus of the Pyrenocarpeae is 

often extremelyreduced, and the perithecia are F 'g- 9- A . e^'^ perithecium of 

J l 

Poiina ohvacea A. L.Sm. x ca.4o; 

then the only Visible portion of the lichen. B, dimidiate perithecium of Acro- 

A few lichens among Graphidineae and 

Pyrenocarpeae grow in a united body generally looked on as a stroma; 

but Wainio 1 has demonstrated that as the fruiting bodies give rise to this 

structure by agglomeration by the cohesion of their margins it can only 

be regarded as a pseudostroma. Two British genera of Pyrenolichens, 

Mycoporum and Mycoporellum, exhibit this pseudo-stromatoid formation. 

C. DEVELOPMENT OF REPRODUCTIVE ORGANS 

As most known lichens belong to the Ascolichens, the study of development 

has been concentrated on that group. Tulasne 2 was the first to make 

a microscopic study of lichen tissues and he described in considerable detail 

the general anatomical structure of apothecia and perithecia. Later, Fuisting :i 

traced the development of a number of perithecia through their different 

stages of growth, but his most interesting discovery was made in Lecidea 

fumosa, a crustaceous Discolichen with an areolate thallus in which the 

apothecia are seated on the fungal hyphae between the areolae. In the very 

early stages represented by a complex of slender hyphae, he observed an 

unbranched septate filament with short cuboid cells, richer in contents than 

the surrounding filaments and somewhat similar to the structure known to 

mycologists as "Woronin's hypha," which is an ascogonial structure. These 

specialized cells disappeared as the hymenium began to form. 

1 Wainio 1890. Tulasne 1852. 

3 

Fuisting 1868.

i6o 

REPRODUCTION 

i. DISCOLICHENS 

a. CARPOGONIA OF GELATINOUS LICHENS. Stahl's 1 work on various 

Collemaceae followed on the same lines as that of Fuisting. The first species 

selected by him for examination, Collema (Leptogium) microphyllum, is a 

gelatinous lichen which grows on old trunks of poplars and willows. It has 

a small olive-green thallus which, in autumn, is crowded with apothecia; 

the spermogones or pycnidia appear as minute reddish points on the edge of 

the thallus. Within the thallus, and midway between the upper and lower 

surface, there arises, as a branch from a vegetative hypha, a many-septate 

filament coiled in spiral form at the base, with the free end growing upwards 

and projecting a short distance above the surface and occasionally forked 

(Fig. 91). The tip-cell is slightly swollen and covered with a mucilaginous 

Fig. 91. Collema microphyllum Ach. Vertical section of 

thallus. a, carpogonium ; b, trichogyne. x 350 (after 

Stahl). 

coat continuous with the mucilage of the thallus. The whole structure, 

characterized by the larger size and by the richer contents of its cells, was 

regarded by Stahl as a carpogonium, the coiled base representing the asco- 

gonium, the upright hypha functioning as the receptive organ or trichogyne, 

comparable to that of the Florideae. The spermatia, which mature at this 

early stage of carpogonial development, are expelled from a neighbouring 

spermogonium on the addition of moisture and easily reach the protruding 

trichogyne. They adhere to the mucilaginous wall of the end-cell, and, in 

two or three instances, Stahl found that copulation had taken place. As the 

affixed spermatium was empty, he concluded that the contents had passed 

over into the trichogyne, and that the nucleus had travelled down to the 

ascogonium. Certain degenerative changes that followed seemed to confirm 

.6 

1 Stahl 1877.

REPRODUCTION IN DISCOLICHENS 

the view that there had been fertilization: the cells of the trichogynej had 

lost their turgidity and at the same time the cross-walls had swollen con- 

siderably and stood out like knots in the 

hypha (Fig. 92). The ascogonial cells had 

also increased not only in size but in number 

by intercalary division, so that the spiral 

arrangement became obscured. Ascogenous 

hyphae arose from the ascogonial cells, and 

asci cut off by a basal septum were finally 

formed from these hyphae. Lateral branches 

from below the septum also formed asci. 

Stahl's observations were repeated and 

extended by Borzi 1 on another of the Colle- 

maceae, Collema nigrescens. In that plant the 

foliaceous thallus is of thin texture and has 

a distinct cellular cortex. The carpogonia 

were found at varying depths near to the cortical 

region; the ascogonium, of two and a 

half to four spirals, consisted often to fifteen 

cells with very thin walls, the trichogyne of 

five to ten cells, the terminal cell projecting 

above the thallus. Borzi also found spermatia 

Fig. 92. 

fused with the tip-cell. 

A further important contribution was made by Baur" in his study of 

Collema microphyllum Ach. 

Carpogonium and trichogyne after 

copulation x 500 (after Stahl). 

Collema crispum*. There occur in nature two forms of this lichen, one of 

them crowded with apothecia and spermogonia, the other with a more 

luxuriant thallus, but with few apothecia and no spermogonia. On the latter 

almost sterile form Baur found in spring and again in autumn immense 

numbers of carpogonia about one thousand in a medium sized thallus 

which nearly all gradually lost the characteristics of reproductive organs, 

and, anastomising with other hyphae, became part of the vegetative system. 

In a few cases in which, presumably, a spermatium had fused with a tricho- 

gyne, very large apothecia had developed. 

As the first-mentioned form was always crowded with apothecia in every 

stage of development, as well as with carpogonia and it spermogonia, seemed 

natural to conclude that the difference was entirely due to the presence or 

absence of spermatia in sufficient numbers to ensure fertilization. The 

period during which copulation is possible passes very rapidly, though 

subsequent development is slow, occupying about half-a-year 

of fertilization to the formation of the first ascus. 

161 

from the time 

1 

Borzi 2 

1878. 

Baur 1898. 

3 

Fiinfstiick (1902) suggests that the lichen worked at by Baur is Collema cheileuni Ach.

I62 

REPRODUCTION 

Baur confirmed Stahl's observations on the various developmental 

changes. In several instances he found a spermatium fused with the tricho- 

gyne, though he could not see continuity between the lumina of the fusing 

cells. After copulation with the spermatium the trichogyne nucleus, which 

occupied the lower third of the terminal cell, had disappeared, and the 

plasma contents had acquired a deeper tint; the other trichogyne cells, 

which had also lost their nuclei, were partly collapsed owing to the pressure 

of the surrounding tissue, and openings were plainly visible through some 

of the swollen septa, especially of the lower cells. In addition the ascogonial 

cells, all of which were uninucleate, had increased in number by intercalary 

division. Plasma connections were opened from cell to cell, but only in the 

primary septa, the later formed cell-membranes being continuous. Ascogenous 

hyphae had branched out from the ascogonium as a series of 

uninucleate cell rows from which the asci finally arose. 

Baur's interpretation was that the first cell of the ascogonium reached 

by the male nucleus after its passage down through the cells of the trichogyne 

represented the egg-cell, and that, after fusion, the resultant nucleus divided, 

and a daughter nucleus passed on to the other auxiliary-cells. No male 

nucleus nor fusion of nuclei was, however, observed by him, and his deduc- 

tions rest on conjecture. 

Krabbe 1 and after him Maule 2 found in Collema pulposum reproductive 

organs similar to those described by Stahl, but in a recent paper on an 

American form of that species a peculiar condition has been described 

by Freda Bachmann 3 . She 4 found that the spermatia originated, not in 

spermogonia, but as groups of cells budded off from vegetative hyphae 

within the tissue of the lichen and occupying the same position as spermo- 

gonia, i.e. the region close below the upper surface. The trichogynes, therefore, 

never emerged into the open, but travelled towards these internal spermatia, 

and fusion with them was effected. The changes that afterwards took place 

in the carpogonial cells were similar to those that had been recognized by 

Stahl and Baur as consequent on fertilization. 

Additional cytological details have been published in a subsequent 

paper 5 : after fusion with the spermatium the terminal cell of the trichogyne 

collapsed, its nucleus became disintegrated and the cross septa of the lower 

trichogyne cells became perforated, these perforations being closed again at 

a later stage by a gelatinous plug. The nuclear history is more doubtful : 

the disappearance of the nuclei from the spermatium and from the terminal 

cell of the trichogyne was noted; two nuclei were seen to be present in the 

penultimate cell, and these the author interpreted as division products of the 


2 Maule 1891. 

3 F. Bachmann 1912. 

4 This species of Collema has been described as Collemodes Bachmanniantim by Bruce Fink 1918. 

5 F. Bachmann 1913.

REPRODUCTION IN DISCOLICHENS 163 

original cell nucleus. In the same cell, lying close against the lower septum 

and partly within the opening, there was a mass of chromatin material which 

might be the male nucleus migrating downwards. The next point of interest 

was observed in the twelfth cell from the tip in which there were two nuclei, 

a larger and a smaller, the latter judged to be the male cell, the small size 

being due to probable division of the spermatium nucleus either before or 

after leaving the spermatium. It is stated however that the spermatium 

was always uninucleate. Meanwhile the cells of the ascogonium had 

increased in size, the perforations of the septa between the cells became 

more evident, and their nuclei persisted. In one cell at this stage two nuclei 

were present, one of the two presumably a male nucleus; no fusion of nuclei 

was observed in the ascogonial cells. Later the cross walls between the 

cells were seen to have disappeared more completely and migration of 

nuclei had taken place, so that some of the cells appeared to be empty while 

others were multinucleate. Considerable multiplication of the nuclei occurred 

before the ascogenous hyphae were formed : twelve nuclei were observed in 

a part of the ascogonium which was just beginning to give off a branch. 

Several branches might arise from one cell, and their cells were either uni- 

or binucleate, the nuclei being larger than those of the vegetative hyphae. 

The formation of the asci was not distinctly seen, but young binucleate 

asci were not uncommon. The fusion of the two nuclei was followed by 

the enlargement of the ascus and the subsequent nuclear division for spore 

formation. In the first heterotypic division twelve chromosomes, double the 

number observed in the vegetative nucleus, were counted on the equatorial 

plate. In the third division they were reduced to the normal number of six, 

from which F. Bachmann concludes that a twofold fusion must have taken 

place 

in the ascogonium and again in the ascus. 

Spiral or coiled ascogonia were observed by Wainio 1 in the gelatinous 

crustaceous genus Pyrenopsis, but the trichogynes did not reach the surface. 

In Lichina-, a maritime gelatinous lichen where the carpogonia occur in 

groups, trichogynes have not been demonstrated. 

A peculiarity of some gelatinous lichens noted by Stahl 3 and others in 

species of Pkysma, and by Forssell 4 in Pyrenopsis and Psorotichia, is the 

development of carpogonia at the base of, and within the perithecial walls 

of old spermogonia. No special significance is however attached to this 

phenomenon, and it is interesting to note that a similar growth was observed 

by Zukal 5 in a pyrenomycetous fungus, Pleospora collematum, a harmless 

parasite on PJiysma compactum and other Collemaceae. The structures invaded 

were true pycnidia of the fungus as the minute spores were seen to 

germinate. A " Woronin's hypha " at the base of several of these pycnidia 

developed asci which pushed up among the spent sporophores. 

1 Wainio i. 1890. 

2 Wolff 1905. 

3 Stahl 1877. 

4 Forssell 1885'-. 

a Zukal 1887, p. 42. 

II 2

1 64 

REPRODUCTION 

b. CARPOGONIA or NON-GELATINOUS LICHENS. The soft loose tissue 

of the gelatinous lichens is more favourable for the minute study of apo- 

thecial development than the closely interwoven hyphae of non-gelatinous 

forms, but Borzi 1 had already extended the study to species of Parmelia, 

Anaptychia, Sticta, Ricasolia and Lecanora, and in all of them he succeeded 

in establishing the presence of ascogonia and trichogynes. After him a 

constant succession of students have worked at the problem of reproduction 

in lichens. 

Lindau 2 

published results of the examination of a considerable series of 

lichens. In Anaptychia (Physcia) ciliaris, Physcia stellaris, Ph. pulverulenta, 

Ramalina fraxinea, Placodium (Lecanora) saxicolum, Lecanora subfusca and 

Lecidea enteroleuca he demonstrated the presence of ascogonia with tricho- 

gynes. In Parmelia tiliacea and in Xanthoria parietina he found ascogonia 

but failed to see trichogynes. In none of the species examined by him did 

he observe any fusion between the trichogyne and a spermatium. 

In Anaptychia ciliaris he was able to pick out extremely early stages by 

staining with a solution of chlor-zinc-iodine. 

3 Maule applied the same test 

to Physcia pulverulenta, but found that to be successful the reaction required 

some time. Certain cells of the hyphae mostly 

terminal cells in the lower area of the gonidial 

zone and even occasionally in the pith (according 

to Lindau) coloured a deep brown, while the 

Fig. 93. Pkyscia pulverulenta Nyl. 

Vertical section of thallus and 

carpogonium before fertilization. 

a, outer cortex; b, inner cortex; 

c, gonidial 1 ayer ; d, medulla, 

x ca. 540 (after Darbishire). 

ordinary thalline hyphae were tinted yellow. 

He assumed that these were initial ascogonial 

cells on account of the richer plasma contents, 

and also because of the somewhat larger size of 

the cells. In the same region of the thallus 

young carpogonia were observed as outgrowths 

from vegetative hyphae, though the trichogynes 

had not yet reached the surface. 

At a more advanced stage the carpogonia 

were seen to be embedded in the gonidial zone 

and occurred in groups. The cells of the asco- 

gonium, easily recognized by the darker stain, 

were short and stout, measuring about 6-8 /j, in 

length and 4*4 p, in width. They were arranged 

in somewhat indistinct spirals; but the crowding 

of the groups resulted in a confused intermingling of the various generative 

filaments. The trichogynes composed of longer narrower cells rose above 

the hyphae of the cortex; they also stained a deep brown and the projecting 

cell was always thin-walled. Lindau frequently observed spermatia very 

1 Borzi 1878. 

2 Lindau 1888. 3 Maule 1891.


firmly attached to the trichogyne cell but without any plasma connection 

between the two. The changes in the trichogyne described by Stahl and 

Baur in Collemaceae were not seen in Anaptychia\ the peculiar swelling of 

the septa seems to be a phenomenon confined to gelatinous lichens. During 

the trichogyne stage in this lichen the vegetative hyphae from the medulla 

grow up and surround the young carpogonia, and, at the same time, very 

slender hyphae begin to branch upwards to form the paraphyses. Darbi- 

shire's 1 examination of Physcia pulvernlenta demonstrated the presence of 

the coiled ascogonium and the trichogyne in that species (Fig. 93). 

Baur 1 has also given the results of an examination of Anaptychia. He 

frequently observed copulation between the spermatium and the tip- of the 

trichogyne, but not any passage of nucleus or contents. After copulation 

the ascogonial cells increased in size and became irregular in form, and 

open communication was established between them (Fig. 94). There was 

no increase in their number by intercalary division as in Collema. After 

Fig. 94. Physcia {Anaptychia) ciliaris DC. Vertical 

section of developing ascogonium. a, paraphyses ; 

b, ascogonial hyphae; c, ascogonial cells, x 800 (after 

Baur). 

producing ascogenous hyphae the cells were seen to have lost their contents 

and then to have gradually disappeared. The fertile hyphae, which now 

took a blue colouration with chlor-zinc-iodine, gradually spread out and 


2 Baur 1904.

1 66 

REPRODUCTION 

formed a wide-stretching hymenium. Several carpogonia took part in the 

formation of one apothecium. 

The tissue below the ascogonium meanwhile developed vigorously, form- 

ing a weft of encircling hyphae, while the upper branches grew vertically towards 

the cortex. Gonidia in contact with the developing fruit also increased, 

and, with the hyphae, formed the exciple or thalline margin. The growth 

upward of the paraphyses raises the overlying cortex which in Anaptychia 

is " fibrous "; it gradually dies off and allows the exposure of the disc, though 

small shreds of dead tissue are frequently left. In species such as those of 

Xanthoria where the cortex is of vertical cell-rows, the apothecial hyphae 

simply push their way between the cell-rows and so through to the open. 

Baur found the development of the apothecium somewhat similar in the 

crustaceous corticolous lichen, Lecanora subfusca. After a long period of 

sterile growth, spermogonia appeared in great abundance, and, a little later, 

carpogonia in groups of five to ten ; the trichogynes emerged very slightly 

above the cortex; they were now branched. The ascogonia were frequently 

a confused clump of cells, though sometimes they showed distinct spirals. 

The surrounding hyphae had taken a vertical direction towards the cortex 

at a still earlier stage, and the brown tips were visible on the exterior before 

the trichogynes were formed. The whole growth was extremely slow. 

In Physcia stellaris the carpogonia occurred in groups also, though Lin- 

dau 1 thinks that, unlike Anaptychia (Physcia} ciliaris, only one is left to form 

the fruit. Only one, according to Darbishire 2 , entered into the apothecium 

in the allied species, Physcia pulverulenta. In the latter plasma connections 

were visible from cell to cell of the trichogyne, and, after copulation with 

the spermatium, the ascogonial cells increased in size though not in number 

and the plasma connections between them became so wide that the asco- 

gonium had the appearance of an almost continuous multinucleate cell or 

coenogamete 3 . As in gelatinous lichens, each of these cells gave rise to 

ascogenous hyphae. 

c. GENERAL SUMMARY. The main features of development described 

above recur in most of the species that have been examined. 

(i) The carpogonia arise in a complex of hyphae situated on the under 

side of, or immediately below the gonidial zone. Usually they vary in number 

from five to twenty for each apothecium, though as many as seventy-two 

have been computed for Icmadophila ericetorum*, and Wainio 5 describes 

them as so numerous in Coccocarpia pellita var., that their trichogynes covered 

some of the young apothecia with a hairy pile perceptible with a hand lens, 

though at the same time other apothecia on the same specimens were 

bsolutely smooth. 



3 See also p. 180. 

4 


5 Wainio i. 1890.


(2) The trichogynes, when present, travel up through the gonidial and 

cortical regions of the thallus; Darbishire 1 observes that in Physcia pulveru- 

lenta, they may diverge to the side to secure an easier course between the 

groups of algae. They emerge above the surface to a distance of about 1 5/i 

or less; after an interval they collapse and disappear. Their cells, which are 

longer and narrower than those of the ascogonium, are uninucleate and vary 

in number according to species or to individual lichens. Baur 2 

thought that 

possibly several trichogynes in succession might arise from one ascogonium. 

(3) How many carpogonia share in the development of the apothecium 

is still a debated question. In Collema only one is 

functional. Baur 3 was unable to decide if one or 

more were fertilized in Parmelia acetabulum, and 

in Usnea Nienburg 4 found that, out of several, one 

alone survived (Fig. 95). But in Anaptychia ciliaris 

and in Lecanora subfusca Baur 3 considers it proved 

that several share in the formation of the apothecium. 

In this connection it is interesting to note that, 

according to Harper 5 and others, several ascogonia 

enter into one Pyronema fruit. 

(4) The ascogonial cells, before and after fertilization, 

are distinguished from the F 

surrounding 'g; 95- 

~ 

Vsneabarbata\jl&>. 

Carpogonium with trichohyphae 

by a reaction to various stains, which is dif- gynex uoo (after Nien- 

bur 

ferent from that of the vegetative hyphae, and s)- 

also 

by the shortness and width of their cells. The whole of the apothecial primordium 

is generally recognizable by the clear shining appearance of the cells. 

(5) *The ascogonia do not always form a distinct spiral; frequently they 

lie in irregular groups. Each cell is uninucleate and may ultimately produce 

ascogenous hyphae, though in Anaptychia Baur 3 noted that some of the 

cells failed to develop. 

(6) The hyphae from the ascogonial cells spread out in a complex layer 

at the base of the hymenium, and send up branches which form the asci, 

either, as in most Ascomycetes, from the penultimate cell of the fertile branch, 

or from the last cell, as in Sphyridium (Baeomyces rufus)* and in Baeomyces 

roseus. The same variation has been observed in fungi in a species of 

Peziza 6 

, in which it is the end-cell of the branch that becomes the mother- 

cell of the ascus; but this deviation from the normal is evidently of rare 

occurrence either in lichens or fungi. 

d. HYPOTHECIUM AND PARAPHYSES. The hypothecium is the layer of 

hyphae that subtends the hymenium, and is formed from the complex of 


5 

Harper 1900. 

2 Baur 1901. 

3 Baur 1904. 

6 Guilliermond 1904, p. .60. 

4 

Nienburg 1908.

1 68 

REPRODUCTION 

hyphae that envelope the first stages of the carpogonia. It is vegetative in 

origin and distinct from the generative system. 

In lichens belonging to the Collemaceae, the paraphyses rise from the 

branching of the carpogonial stalk-cell immediately below the ascogonium 1 

, 

but have no plasma connection with it. They are thus comparable in origin 

with the paraphyses of many Discomycetes. 

In several genera in which the algal constituents are blue-green, such as 

Stictina, Pannaria, Nephroma, Ricasolia and Peltigera, Sturgis 2 found that 

reproduction was apogamous and also that asci and paraphyses originated 

tuft of paraphyses arose from the basal cell 

from the same : cell-system a 

of the ascus, or an ascus from the basal cell of a paraphysis. These results 

are at variance with those of most other workers, but the figures drawn by 

Sturgis seem to be clear and convincing. 

Again in Usnea barbata, as described by Nienburg 3 the ., ascogonial cells, 

after the disappearance of the trichogyne, branch profusely not only upwards 

towards the cortex but also downwards and to each side The upward 

branches give rise normally to the asci, the lower branches produce the sub- 

hymenium and later the paraphyses, and the two systems are thus genetically 

connected, though they remain distinct from each other, and asci are never 

formed from the lower cells. 

In most heteromerous lichens, however, the origin of the paraphyses 'is 

exclusively vegetative: they arise as branches from the primordial complex 

that forms the covering hyphae of the ascogonium both above and below. 

Schwendener 4 had already pointed out the difference in origin between the 

two constituents of the hymenium in one of his earlier studies on the development 

of the apothecium, and this view has been repeatedly confirmed 

by recent workers, except by Wahlberg 5 who has insisted that they rise from 

the same cells as the asci, a statement disproved by Baur 6 . The paraphyses 

originate not only from the covering hyphae, but from vegetative cells in 

close connection with the primordium. In this mode of development, lichens 

diverge from fungi, but even in these a vegetative origin for the paraphyses 

has been pointed out in Lachnea scutellata? where they branch from the 

hyphae lying round the ascogonium. 

There is no general rule for the order of development. In Lecanora sub- 

fusca Baur 6 found that vertical filaments had reached the surface by the time 

the trichogyne was formed, and their pointed brown tips gave a ready clue 

to the position of the carpogonia. In Lecidea enteroleuca* they show their 

characteristic form and arrangement before there is any trace of ascus 

formation. In Solorina* they are well formed before the ascogenous 

hyphae appear. In other lichens such as Placodium saxicolum*, Peltigera 

1 Baur 3 

4 5 

1899. Sturgis 1890. Nienburg 1908. Schwendener 1864. Wahlberg 1902. 

6 

Baur 7 

1904. 

Brown 8 9 

1911. 

Moreau 1916. 

Lindau 1888.


rufescens 1 and P. malacea* the two systems paraphyses and ascogonium 

grow simultaneously, though in P. horizontalis the ascogonium has disappeared 

by the time the paraphyses are formed. In the genus Nephroma, 

in Physcia stellaris and in Xanthorina parietina the paraphyses are also late 

in making their appearance. 

In most instances, the paraphyses push their way up between the cortical 

cells which gradually become absorbed, or they may stop short of the sur- 

face as in Nephromium tomentosum*. The overlying layer of cortical cells in 

that case dies off gradually and in time disappears. Such an apothecium is 

said to be " at first veiled." Later formed paraphyses at the circumference 

of the apothecium form the parathecium, which is thus continuous with the 

hypothecium. 

e. VARIATIONS IN APOTHECIAL DEVELOPMENT. Lichens are among 

the least stereotyped of plants : instances of variation have been noted in 

several genera. 

aa. PARMELIAE. A somewhat complicated course of development has 

been traced by Baur 2 in Parmelia acetabulum. In that lichen the group of 

three to six carpogonia do not lie free in 

the gonidial tissue, but originate nearer 

the surface (Fig. 96) and are surrounded 

from the first by a tissue connected with, 

and resembling the tissue of the cortex. 

In the several ascogonia, there are more 

cells and more spirals than in Collema 

or in Physcia, and all of them are some- 

what confusedly intertwined. The tri- 

chogynes are composed of three to five 

cells and project 10 to I5ytt above the 

surface. When further development be- 

gins, the ascogonial cells branch out and 

form a primary darker layer or hypox 

55 (after Baur). 

thecium above which extends the subhymenium, a light-coloured band of 

loosely woven hyphae. Branches from the ascogonial hyphae at a later stage 

push their way up through this tissue and form above it a second plexus of 

hyphae the base of the hymenium. Baur considers this a very advanced 

type of apothecium; he found it also present in Parmelia saxatilis, though, 

in that species, the further growth of the first ascogonial layer was more 

rapid and the secondary plexus and hymenium were formed earlier in the 

life of the apothecium. He has also stated that a similar development occurs 

in other genera such as Usnea, though Nienburg's 3 work scarcely confirms 

that view. 

1 Funfsttick 1884. 

* Baur 1904. 

3 Nienburg 1908.

i ;o 

REPRODUCTION 

In the brown Parmeliae, Rosendahl 1 found the same series of apothecial 

tissues, but he interprets the course of development somewhat differently: 

the basal dark layer or hypothecium he found to be of purely vegetative 

origin ; above it extended the lighter-coloured subhymenium ; the ascogenous 

hyphae were present only in the second layer of dark tissue immediately 

under the hymenium. 

In most lichens the primordium of the apothecium arises towards the 

lower side of the gonidial zone, the hyphae of which retain the meristematic 

character. In Parmeliae, as was noted by Lindau 2 in P. tiliacea, and by 

Baur 3 and Rosendahl 1 in other species, the carpogonial groups are formed 

above the gonidial zone, either immediately below the cortex as in P. glabra- 

tula, or in a swelling of the cortex itself as in P. aspidota, in which species 

the external enlargement is visible by the time the trichogynes reach the 

surface. In P. glabra, with a development entirely similar to that of P. as- 

pidota, no trichogynes were seen at any stage. The position of the primordium 

close under the cortex is also a feature of Ramalina fraxinea as described 

G. Wolff4 The 

trichogynes in that species are fairly numerous. 

. by 

A further peculiarity in Parmelia acetabulum attracted Baur's 3 attention. 

Carpogonia with trichogynes are extremely numerous in that species as are 

the spermogonia, the open pores of which are to be found everywhere between 

the trichogynes, and yet fertilization can occur but rarely, as disintegrating 

carpogonia are abundant and very few apothecia are formed. Baur makes 

the suggestion that possibly cross-fertilization may be necessary, or that the 

spermatia, in this instance, do not fertilize and that development must 

therefore be apogamous, in which case the small number of fruits formed is 

due to some unknown cause. Fiinfstuck 5 

thought that degeneration of the 

carpogonia had not gone so far, but that a few had acquired the power to 

develop apogamously. In Parmelia saxatilis only a small percentage of 

carpogonia attain to apothecia, although spermogonia are abundant and in 

close proximity, but in that species, unlike P. acetabulum, a large number 

the more vigorous apothecia seem 

reach the earlier stages of fruit formation ; 

to inhibit the growth of those that lag behind. 

bb. PERTUSARIAE. In Pertusaria, the apothecial primordium is situated 

immediately below the gonidial zone; the cells have a somewhat larger 

lumen and thinner walls than those of the vegetative hyphae. In the asco- 

gonium there are more cells than in Parmelia acetabulum] the trichogynes 

are short-lived, and several carpogonia probably enter into the formation of 

each apothecium ; the paraphyses arise from the covering hyphae. So far the 

course of development presents nothing unusual. The peculiar pertusarian 

feature as described by Krabbe 6 

, and after him by 


5 Funfstiick 1902. 

2 Lindau 1888. 3 Baur 1904. 

6 Krabbe 1882. 7 Baur 1901. 

7 Baur does not , 

appear 

4 Wolff 1905.


till a later stage. By continual growth in thickness of the overlying 

thallus, the apothecia gradually become submerged and tend to degenerate; 

meanwhile, however, a branch from the ascogonial hyphae at the base of 

the hymenium pushes up along one side and forms a secondary ascogonial 

cell-plexus over the top of the first-formed disc. A new apothecium thus 

arises and remains sporiferous until it also comes to lie in too deep a position, 

when the process is repeated. Sometimes the regenerating hypha travels to 

the right or left away from the original apothecium, it may be to a distance 

of 2 mm. or according to Fiinfstiick even considerably farther. Funfstiick 1 has 

gathered indeed from his own investigations that such cases of regeneration 

are by no means rare : ascogenous hyphae, several centimetres long, destined 

to give rise to new apothecia are not unusual, and their activity can be recog- 

Fig. 97. Rhizocarpon petraeum Massal. Concentrically arranged apothecia, reduced 

(J. Adams, Photo.}. 

nized macroscopically by the linear arrangement of the apothecia in such 

lichens as RJiizocarpon (petraeuwi) concentricum (Fig. 97). 

In Variolaria, a genus closely allied to or generally included in Per- 

tusaria, Darbishire 2 has described the primordial tissue as taking rise almost 

at the base of the crustaceous thallus: strands of delicate hyphae, staining 

1 Ftinfstiick 1902. 

2 Darbishire 1897.

172 

REPRODUCTION 

blue with iodine, mount upwards from that region through the medulla and 

gonidial 

reached. 

zone 1 

. The 

ascogonium does not appear till the surface is almost 

cc. GRAPHIDEAE. Several members of the Graphidaceae were studied 

by G. Wolff 2 : 

she demonstrated the presence of carpogonia with emerging 

trichogynes in Graphis elegans, a species which is distinguished by the deeply 

furrowed margins of the lirellae (Fig. 89). Before the carpogonia appeared 

it was possible to distinguish the cushion-like primordial tissue of the apo- 

thecium in the thallus which is almost wholly immersed in the periderm 

layers of the bark on which it grows. The trichogynes were very sparingly 

septate, and a rather large nucleus occupied a position near the tip of the 

terminal cell. The dark carbonaceous outer wall makes its appearance in 

this species at an early stage of development along the sides of the lirellae, 

but never below, as there is always a layer of living cells at the base. After 

the first-formed hymenium is exhausted, these basal cells develop a new 

apothecium with a new carbonaceous wall that pushes back the first-formed, 

leaving a cleft between the old and the new. This regenerating process, 

somewhat analogous to the formation of new apothecia in Pertusaria, may 

be repeated in Graphis elegans as many as five times, the traces of the older 

discs being clearly seen in the channelled margins of the lirellae. 

dd. CLADONIAE. The chief points of interest in the Cladoniae are the 

position of the apothecial primordia and the function of the podetium, 

which are discussed later 3 . Krabbe 4 determined 

not only the endogenous origin of 

Fig. 98. Cladonia decorticata Spreng. Vertical 

section of squamule and primordium 

of podetium. a, developing podetium; 

b, probably fertile hyphae; c, cortical 

tissue ;


branches push up between them and gradually a compact sheath of para- 

physes is built up. The ascogenous hyphae meanwhile spread radially at 

the base of the paraphyses and the asci begin to form. The apothecia may 

be further enlarged by intercalary growth, and this vigorous development 

of vegetative tissue immediately underneath raises the whole fruit structure 

well above the surface level. 

Sattler 1 in his paper on Cladoniae* cites as an argument in favour of 

fertilization the relative positions of carpogonia and spermogonia on the 

podetia. The carpogonia with their emerging trichogynes being situated 

rather below the spermogonia. Both organs, he states, have been demon- 

strated in eleven species; he himself observed them in the primordial podetia 

of Cladonia botrytes and of Cl. Floerkeana. 

2. PYRENOLICHENS 

a. DEVELOPMENT OF THE PERITHECIUM. It is to Fuisting 3 that we 

owe the first account of development in the lichen perithecium. Though 

he failed to see the earlier stages (in Verrucaria Dufourii), he recognized 

the primordial complex of hyphae in the gonidial zone of the thallus, from 

which originated a vertical strand of hyphae destined to form the tubular 

neck of the perithecium. Growth in the lower part is in abeyance for 

a time, and it is only after the neck is formed, and the fruiting body is 

widened by the ingrowth of external hyphae, that the asci begin to branch 

up from the tissue at the base. 

b. FORMATION OF CARPOGONIA. Stahl 4 had indicated that not only 

in gymnocarpous but also in angiocarpous 

lichens, it would be found that carpo- 

were formed as in Collema. 

3 Baur 

gonia 

justified this surmise, and demonstrated the 

presence of ascogonia in groups of three to 

eight, with trichogynes that reached the 

surface in Endocarpon {Dermatocarpon) mi- 

niatum (Fig. 99). It is one of the few 

foliaceous Pyrenolichens, and the leathery 

thallus is attached to the substratum by a 

central point, thus allowing in the thallus 

not only peripheral but also intercalary 

growth, the latter specially active round the 

point of basal attachment; carpogonia may 

be found in any region where the tissue is Fig. 99. Dermatocarpon miniatum 

3 

. . Th. Fr. Vertical section of thallus 

, 

newly formed, and at any season. I he upper and carpogonial group x 600 (after 

cortex is composed 

1 Sattler 1914. 

of short-celled thick- 

~ See Chap. VII. 3 Fuisting 18 

Baur). 

4 Stahl 1877. Baur 1904.

i 74 

REPRODUCTION 

walled hyphae, with branching vertical to the surface, and so closely packed 

that there is an appearance of plectenchyma ; the medullary hyphae are 

also thick-walled but with longer cells. The carpogonia of this species 

arise as a branch from the vegetative hyphae and are without special covering 

hyphae, so frequent a feature in other lichens. The trichogynes bore their 

nay through the compact cortex and rise well above the surface. After they 

have disappeared presumably after fertilization the vegetative hyphae 

round and between the ascogonia become active and travel upwards slightly 

converging to a central point. The asci begin to grow out from the asco- 

genous hyphae of the base before the vertical filaments have quite pierced 

the cortex. 

Pyrenula nitida has also been studied by Baur 1 . It is a very common 

species on smooth bark, with a thin crustaceous thallus immersed among 

the outer periderm cells. Unlike most other lichens, it forms carpogonia 

in spring only, from February to April. A primordial coil of hyphae lies at 

the base of the gonidial layer, and, before there is any appearance of carpo- 

so that a 

gonia, a thick strand of hyphae is seen to be directed upwards, 

definite form and direction is given to the perithecium at a very early stage. 

The ascogonial cells which are differentiated are extremely small, and, like 

those of all other species examined, are uninucleate. There are five to ten 

carpogonia in each primordium the ; trichogynes grow up through the hyphal 

strand and emerge 5-10 /* above the surface. After their disappearance, a 

weft of ascogenous tissue is formed at the base, and, at the same time, the 

surrounding vegetative tissue takes part in the building up of a plectenchymatous 

wall of minute dark-coloured cells. Further development is 

rapid and occupies probably only a few weeks. 

In many of the pyrenocarpous lichens Verrucariae and others the 

walls of the paraphyses dissolve in mucilage as the spores become mature, 

a character associated with spore ejection and dispersal. In some genera 

and species, as in Pyrenula, they remain intact. 

D. APOGAMOUS REPRODUCTION 

Though fertilization by an externally produced male nucleus has not 

been definitely proved there is probability that, in some instances, the fruit 

may be the product of sexual fusion. There are however a number of genera 

and species in which the development is apogamous so far as any external 

copulation is possible and the sporiferous tissue seems to be a purely vegetative 

product up to the stage of ascus formation. 

In Phlyctis agelaea Krabbe 2 found abundant apothecia developing nor- 

mally and not accompanied by spermogonia; in Phialopsis rubra studied 

1 Baur 1901. 

2 Krabbe 1882.

APOGAMOUS REPRODUCTION 175 

also by him the primordium arises among the cells of the periderm on which 

the lichen grows, and he failed to find any trace of a sexual act. In his 

elaborate study of Gloeolichens Forssell 1 established the presence of carpo- 

gonia with trichogynes in two species Pyrenopsis phaeococca and P. impolita, 

but without any appearance of fertilization; in all the others examined, the 

origin of the fruit was vegetative. Wainio 2 records a similar observation in 

a species of Pyrenopsis in which there was formed a spiral ascogonium and 

a triehogyne, but the latter never reached the surface. 

Neubner 3 claimed to have proved a vegetative origin for the asci in the 

Caliciaceae; but he overlooked the presence of spermogonia and his conclu- 

sions are doubtful. 

Fiinfstuck 4 found apogamousdevelopment inPeltigera(\r\c\\idmgPeltidea) 

and his results have never been disputed. The ascogonial cells are surrounded 

at an early stage by a weft of vegetative hyphae. No trichogynes are formed 

and spermogonia are absent or very rare in the genus, though pycnidia with 

macrospores occur occasionally. 

Some recent work by Darbishire 5 on the genus supplies additional details. 

The apothecial primordium always originated near the growing margin of 

the thallus, where certain medullary hyphae were seen to swell up and stain 

more deeply than others. These at first were uninucleate, but the nuclei 

increased by division as the cells became larger, and in time there was 

" 

formed a mass of closely interwoven cells full of cytoplasm. No coiled 

carpogonia can be made out, but these darkly stained cells form part of a 

connected system of branching hyphae coming from the medulla further 

back." Long unbranched multiseptate hyphae evidently functionless tri- 

chogynes travelled towards the cortex but gradually died off. Certain of 

the larger cells the " 

ascogonia " 

grew out as ascogenous hyphae into 

which the nuclei passed in pairs and finally gave rise to the asci. 

These results tally well with those obtained by M. and Mme Moreau 6 

though they make no mention of any triehogyne. They found that the 

terminal cells of the ascogenous hyphae were transformed into asci, and the 

two nuclei in these cells fused the only fusion that took place. In Nephromtum, 

one of the same family, the case for apogamy is not so clear; but 

Fiinfstuck found no trichogynes, and though spermogonia were present on 

the thallus, they were always somewhat imperfectly developed. 

Sturgis 7 

supplemented these results in his study of other lichens con- 

taining blue-green algae. In species of Heppia, Pannarta, Hydrothyria, 

Stictina and Ricasolia, he failed to find any evidence of fertilization by 

spermatia. 

Solorina, also a member of Peltigeraceae, was added to the list of 

1 

Forssell 1885. 

2 Wainio 1890, p. 

x. 

3 Neubner 1893. 

4 Fiinfstuck 1884. 

5 



7 

Sturgis 1890. 

,

i 76 

REPRODUCTION 

apogamous genera by Metzger 1 and his work was confirmed and amplified 

by Baur 2 : certain hyphae of the gonidial zone branch out into larger asco- 

gonial cells which increase by active intercalary growth, by division and by 

branching, and so gradually give rise to the ascogenous hyphae and finally 

to the asci. Baur looked on this and other similar formations as instances 

of degeneration from the normal carpogonial type of development. Moreau 3 

(Fernand and Mme) have also examined Solorina with much the same 

results: the paraphyses rise first from cells that have been produced by the 

gonidial hyphae; later, ascogenous hyphae are formed and spread horizontally 

at the base of the paraphyses, finally giving rise at their tips to the asci. 

Metzger 1 had further discovered that spermogonia were absent and tricho- 

gynes undeveloped in two very different crustaceous lichens, Acarospora 

(Lecanora) glaucocarpa and Verrucaria calciseda, the latter a pyrenocarpous 

species and, as the name implies, found only on limestone. 

Krabbe 4 had noted the absence of any fertilization process in Gyrophora 

vellea. At a later date, Gyrophora cylindrica was made the subject of exact 

research by Lindau 5 . In that species the spermogonia (or pycnidia) are 

situated on the outer edge of the thallus lobes; a few millimetres nearer the 

centre appear the primordia of the apothecia, at first without any external 

indication of their presence. The initial coil which arises on the lower side 

of the gonidial zone consists of thickly wefted hyphae with short cells, slightly 

thicker than those of the thallus. It was difficult to establish their connec- 

tion with the underlying medullary hyphae since these very soon change to a 

brown plectenchyma. From about the middle of the ascogonial coil there 

rises a bundle of parallel stoutish hyphae which traverse the gonidial zone 

and the cortex and slightly overtop the surface. They are genetically con- 

nected at the base with the more or less spirally coiled hyphae, and are similar 

to the trichogynes described in other lichens. Lindau did not find that they 

had any sexual significance, and ascribed to them the mechanical function of 

terebrators or borers. The correctness of his deductions has been disputed by 

various workers: Baur 2 looks on these "trichogynes" as the first paraphyses. 

The reproductive organs in Stereocaulon were examined by G. Wolff 6 and 

, 

the absence of trichogynes was proved, though spermogonia were not wanting. 

She also failed to find any evidence of fertilization in Xanthoria parietina, 

in which lichen the ascogenous hyphae branch out from an ascogonium that 

does not form a trichogyne. 

Rosendahl 7 

, as already stated, could find no trichogynes in Parmelia 

glabra. In Parmelia obscurata, on the contrary, Bitter 8 found that carpogonia 

with trichogynes were abundant and spermogonia very rare. In other species 

of the subgenus, Hypogymnia, he has pointed out that apothecia are either 

1 

2 

Metzger 1903. Baur 1904. 

6 Wolff 1905. 



4 Krabbe 1882. 5 Lindau 1899. 

8 Bitter i9oi 2 .

DISCUSSION OF LICHEN REPRODUCTION 177 

absent or occur but seldom, while spermogonia are numerous, and he concludes 

that the spermatia must function as spores or conidia. Baur 1 however does 

not accept that conclusion; he suggests as probable that the male organs 

persist longer in a functionless condition than do the apothecia. 

Still more recently Nienburg 2 has described the ascogonium of Baeo- 

myces sp. and also of Sphyridium byssoides (Baeomyces rufus) as reduced 

and probably degenerate. His results do not disprove those obtained by 

Krabbe 3 on the same lichen {Sphyridium fungiforme). The apothecia are 

terminal on short stalks in that species. When the stalk is about '5 mm. in 

height, sections through the tip show numerous primordia (12 to 15) ranged 

below the outer cortex, though only one, or at most three, develop further. 

These ascogonial groups are connected with each other by delicate filaments, 

and Nienburg concluded that they were secondary products from a primary 

seen in what he 

group lower down in the tissue. Spirals were occasionally 

considered to be the secondary ascogonia, but usually the fertile cells lie in 

loose uncoiled masses; isolated hyphae were observed to travel upwards 

from these cells, but they never emerged above the surface. 

Usnea macrocarpa if Schulte's 4 work may be accepted is also apo- 

gamous, though in Usnea barbata Nienburg 2 found trichogynes (Fig. 95) 

and the various developments that are taken as evidence of fertilization. 

Wainio 5 had demonstrated emergent straight trichogynes in Usnea laevis 

but without any sign of fertilization. 

E. DISCUSSION OF LICHEN REPRODUCTION 

In Ascolichens fertilization by the fusion of nuclei in the ascogonium 

is still a debated question. The female organ or carpogonium, as outlined 

above, comprises a twisted or spirally coiled multiseptate hypha, with a 

terminal branch regarded as a trichogyne which is also multiseptate, and 

through which the nucleus of the spermatium must travel to reach the 

female cell. It is instructive to compare the lichen carpogonium with that of 

other plants. 

a. THE TRICHOGYNE. In the Florideae, or red seaweeds, in which the 

trichogyne was first described, that organ is merely a hair-like prolongation 

of the egg-cell and acts as a receptive tube. It contains granular proto- 

plasm but no nucleus and terminates in a shiny tip covered with mucilage. 

The spermatium, unlike that of lichens, is a naked cell, and being non-motile 

is conveyed by water to the tip of the trichogyne to which it adheres; the 

intervening wall then breaks down and the male nucleus passes over. After 

this process of fertilization a plug of mucilage cuts off the trichogyne, and 

it withers away. 

1 Baur 1904. 

- 

Xienburg 1908. 

3 Krabbe 1882. 4 Schulte 1904. 


S. L. 12

i 7 8 

REPRODUCTION 

In Coleochaete, a genus of small fresh-water green algae, a trichogyne is 

also present in some of the species: it is again a prolongation of an oogonial 

cell. 

In the Ascomycetes, certain cells or cell-processes associated with the 

ascogonium have been described as trichogynes or receptive cells. In one 

of the simpler types, Monascus 1 the , " trichogyne" is a cell cut off from the 

ascogonial cell. When fertilization takes place, the wall between the two 

cells breaks down to allow the passage of the male nucleus, but closes up 

when the is process effected. In Pyronema confluens* it is represented by a 

process from the ascogonial cell which fuses directly with the male cell. A 

more elaborate "trichogyne " has been evolved in Lachnea stercorea*, another 

Discomycete: in that fungus it takes the form of a 3~5-septate hypha with 

a longer terminal cell; it rises from some part of the ascogonial cell but has 

no connection with any process of fertilization, so that the greater elaboration 

of form is in this case concomitant with loss of function. 

In the Laboulbeniaceae, a numerous and very peculiar series of Asco- 

mycetes that live on insects, there are, in nearly all of the reproductive bodies, 

a carpogonial cell, a trichophoric cell and a trichogyne. The last-named 

organ is in some genera a simple continuous cell, in others it is septate and 

male cells are spermatia of two 

branched, occasionally it is absent 4 . The 

kinds, exogenous or endogenous, and the plants are monoecious or dioecious. 

Laboulbeniaceae have no connection with lichens. Faull 5 a recent worker 

, 

on the group, states that though he observed spermatia attached to the tri- 

chogynes, he was not able to demonstrate copulation (possibly owing to 

over-staining), nor could he trace any migration of the nucleus through the 

trichophoric cell down to the carpogonial cell. In two species of Labotdbenia 

that he examined there were no antheridia, and the egg-cell acquired its 

second nucleus from the neighbouring trichophoric cell. These conjugate 

nuclei divided simultaneously and the two daughter nuclei passed on to the 

ascus and fused, as in other Ascomycetes, to form the definitive nucleus. 

Convincing evidence as to the importance of the trichogyne in fungi was 

supposed, until lately, to be afforded by the presence and functional activity 

of that organ associated with spermogonia in a few Pyrenomycetes in 

Poronia, Gnomonia and Polystigma. Poronia was examined by M. Dawson 6 

who found that a trichogyne-like filament distinct from the vegetative hyphae 

rose from the neighbourhood of the ascogonial cells. It took an upward 

course towards the exterior, but there was no indication that it was ever 

receptive. In Gnomonia erythrostoma and in Polystigma rubrum spermogonia 

with spermatia presumably male organs are produced in abundanceshortly 

before the ascosporous fruit is developed. The spermatia in both cases exhibit 

1 Schikorra 1909. 

2 

5 Faull 1911. 

Harper 1900. 

3 Fraser 1907. 

6 Dawson 1900. 

4 Thaxter 1912.


the characters of male cells, i.e. very little cytoplasm and a comparatively large 

nucleus that occupies most of the cell cavity, along with complete incapacity 

to germinate. Brooks 1 found in Gnomonia that tufts of the so-called tricho- 

gynes originated near the ascogonial cells, but they were " mere continuations 

of ordinary vegetative hyphae belonging to the coil." They are septate and 

reach the surface, and the tip-cell is longer than the others as in the lichen 

trichogyne. 

A somewhat similar arrangement is present in Polystigma, in which 

Blackman and Welsford 2 have proved that the filaments, considered as tri- 

chogynes by previous workers, are merely vegetative hyphae. A trichogynelike 

structure is also present in Capnodium, one of the more primitive Pyreno- 

mycetes, but it has no sexual significance. 

Lindau 3 in his paper on Gyrophora suggested that the trichogyne in 

lichens acted as a " terebrator " or boring apparatus, of service to the deeply 

immersed carpogonium in enabling it to reach the surface. Van Tieghem 4 

explained its presence on physiological grounds as necessary for respiration, 

5 

a view also favoured by Zukal while Wainio , 6 and Steiner 7 see in it only an 

" 

of which is due to its connection with 

end-hypha," the vigorous growth 

the well-nourished cells of the ascogonium. 

Lindau's view has been rejected by succeeding writers: as has been 

outward for 

already stated, it is the paraphyses that usually open the way 

the apothecium. Van Tieghem's theory has been considered more worthy 

of attention and both Dawson and Brooks incline to think that the projecting 

filaments described above may perform some service in respiration, even 

though primarily they may have functioned as sexual receptive organs. 

There is very little support to be drawn from fungi for the theory that 

the presence of a trichogyne necessarily entails fertilization by spermatia. 

Lichens in this connection must be judged as a class apart. 

It has perhaps been too lightly assumed that the trichogyne in lichens 

indicates some relationship with the Florideae 8 . Such a view might be possible 

if we could regard lichens and Florideae as derived from some common 

remote ancestor, though even then the difference in spore production in 

one case exogenous, and in the other in asci and therefore endogenous 

would be a strong argument against their affinity. But all the evidence goes 

to prove that lichens are late derivatives of fungi and have originated from 

them at different points. Fungi are interposed between lichens and any 

other ancestors, and inherited characters must have been transmitted through 

them. F. Bachmann's suggestion 9 that Collema pulposum should be regarded 

" as a link between aquatic red algae and terrestrial ascomycetes such as 

Pyronema and the mildews " cannot therefore be accepted. It seems more 

1 Brooks 1910. 

2 Blackman and Welsford 1912. 

3 

Lindau 1899. 

* Van Tieghem 1891. 

5 Zukal 1895. 


7 

Steiner 1901. 

8 

See also Chap. VII. 9 

F. Bachmann 1913.

i8o 

REPRODUCTION 

probable that the lichen trichogyne is a new structure evolved in response 

to some physiological requirement either sexual or metabolic of the deeply 

embedded fruit primordium. 

b. THE ASCOGONIUM. In fungi there is usually one cell forming the 

ascogonium, a coenogamete, which after fertilization produces ascogenous 

hyphae. There are exceptions, such as Cutting 1 found in Ascophanus carneus, 

in which it is composed of several cells in open contact by the formation of 

is divided 

wide secondary pores in the cell-walls. In lichens the ascogonium 

into a varying number of uninucleate cells. Darbishire 2 

(in Physcia) and 

Baur 3 

(in Anaptychia) have described an opening between the different cells, 

after presumed fertilization, that might perhaps constitute a coenogamete. 

Ascogenous hyphae arise from all, or nearly all the cells, whether fertilized by 

spermatia or not, and asci continue to be formed over a long period of time. 

There may even be regeneration of the entire fruiting body as described in 

Graphis elegans and in Pertusaria, apparently without renewed fertilization. 

Spermogonia (or pycnidia) and the ascosporous fruits generally grow on 

the same thallus, though not unfrequently only one of the two kinds is 

present. As the spermogonia appear first, while the apothecia or perithecia 

are still in the initial stages, that sequence of development seems to add 

support to the view that their function is primarily sexual; but it is equally 

valid as a proof of their pycnidial nature since the corresponding bodies in 

fungi precede the more perfect ascosporous fruits in the life-cycle. 

The differences in fertility between the two kinds of thallus in Collema 

crispum may be recalled 4 . Baur considered that development of the carpo- 

gonia was dependant on the presence of spermatia: a strong argument for 

the necessity of fertilization by these. The conditions in Parmelia acetabulum, 

also recorded by Baur, lend themselves less easily to any conclusion. On 

the thallus of that species the spermogonia and carpogonia present are out 

of all proportion to the very few apothecia that are ultimately formed. 

Though Baur suggested that cross-fertilization might be necessary, he admits 

that the development may be vegetative and so uninfluenced by the presence 

or absence of spermatia. 

It is the very frequent occurrence of the trichogyne as an integral part of 

the carpogonium that constitutes the strongest argument for fertilization by 

spermatia. There is a possibility that such an organ may have been universal 

at one time both in fungi and in lichens, and that it has mostly 

degenerated through loss of function in the former, as it has disappeared in 

many instances in lichens. Again, there is but a scanty and vestigial record 

of spermogonia in Ascomycetes. They may have died out, or they may 

have developed into the asexual pycnidia which are associated with so many 

species. If we take that view we may trace the same tendency in lichens, as 

1 

Cutting 1909. 


3 Baur I94> 

4 See p . l6l .


for instance in the capacity of various spermatia to germinate, though in 

lichen spermogonia there has been apparently less change from the more 

primitive condition. It is also possible that some process of nuclear fusion, 

or more probably of conjugation, takes place in the ascogonial cells, and 

that in the latter case the only fusion, as in some (or most) fungi, is between 

the two nuclei in the ascus. 

If it be conceded that fully developed carpogonia with emergent tricho- 

gynes, accompanied by spermogonia and spermatia, represent fertilization, 

or the probability of fertilization, then the process may be assumed to take 

place in a fairly large and widely distributed series of lichens. Copulation 

between the spermatium and the trichogyne has been seen by Stahl 1 Baur , 

2 

and by F. Bachmann 3 in Collema. In Physcia pulverulenta Darbishire 4 could 

not prove copulation in the earlier stages, but he found what he took to be 

the remains of emptied spermatia adhering to the tips of old trichogynes. 

Changes in the trichogyne following on presumed copulation have been 

demonstrated by several workers in the Collemaceae, and open communi- 

cation as a result of fertilization between the cells of the ascogonium has 

been described in two species. This coenocytic condition of the ascogonium 

(or archicarp), considered by Darbishire and others as an evidence of fertilization, 

has been demonstrated by Fitzpatrick 8 in the fungus Rhizina 

undulata. The walls between the cells of the archicarp in that Ascomycete 

became more or less open, so that the ascogenous hyphae growing from the 

central cells were able easily to draw nutrition from the whole coenocyte, 

but no process of fertilization in Rhizina preceded the breaking down of the 

septa and no fusion of nuclei was observed until the stage of ascus. formation. 

The real distinction between fertile and vegetative hyphae lies, according 

to 

6 

Harper , in the relative size of the nuclei. F. Bachmann speaks of one 

large nucleus in the spermatium of Collema pulposum which would indicate 

sexual function. There is however very little nuclear history of lichens known 

at any stage until the beginning of ascus formation, when fusion of two nuclei 

certainly take place as in fungi to form the definitive nucleus of the ascus. 

The whole matter may be summed up in Fiinfstiick's 7 statement that: 

" 

though research has proved as very probable that fertilization takes place, 

it is an undoubted fact that no one has observed any such process." 

F. FINAL STAGES OF APOTHECIAL DEVELOPMENT 

The emergence of the lichen apothecium from the thallus, and the form 

it takes, are of special interest, as, though it is essentially fungal in structure, 

it is subject to various modifications entailed by symbiosis. 

1 

Stahl 1877. 

2 Baur 1898. 

5 

Fitzpatrick 1918. 

3 F. Bachmann 1912 and 1913. 


6 

Harper 1900. 

7 

Fiinfstttck 1902.

Ig2 

REPRODUCTION 

a. OPEN OR CLOSED APOTHECIA. Schwendener 1 drew attention to two 

types of apothecia directly influenced by the thallus: those that are closed 

at first and only open gradually, and those which are, as he says, open from 

the first. The former occur in genera and species in which the thallus has a 

stoutish cortex, as, for instance, in Lobaria where the young fructification 

has all the appearance of an opening perithecium. The open apothecia 

(primitus apertd) are found in non-corticate lichens, in which case the pioneer 

paraphyses arrive at the surface easily and without any converging growth. 

Similar apothecia are borne directly on the hypothallus at the periphery, or 

between the thalline areolae, and they are also characteristic of thin or slender 

thalli as in Coenogonium. 

In both types of apothecium, the paraphyses .pierce the cortex (Fig. 100) 

and secure the emergence of the developing ascomata. 

Fig. 100. Physcia ciliaris DC. Vertical section of apothecium 

still covered by the cortex, a, paraphyses ; b, hypothecium 

; c, gonidia of thallus and amphithecium. x 150 

(after Baur). 

b. EMERGENCE OF THE ASCOCARP. Hue 2 has taken up this subject in 

recent years and has described the process by which the vegetative hyphae 

surrounding the fruit primordium, excited to active growth by contact with 

the generative system, take part in the later stages of fruit formation. The 

primordium generally occupies a position near to, or just within, the upper 

medulla, and the hyphae in contact with it soon begin to branch freely in a 

vertical direction, surrounding the developing fruit and carrying it upwards 

generally to a superficial position. The different methods of the final emer- 

gence give two very distinct types of mature apothecium: the lecideine in 

which the gonidial zone takes no part in the upward growth, and the leca- 

norine into which the gonidia enter as an integral part. 

In the lecideine series (Fig. 101) the encircling hyphae from the upper 

medulla rise as a compact column through the gonidial zone to the surface 

of the thallus ; they then spread radially before curving up to form the outer 


2 Hue 1906.

DEVELOPMENT OF APOTHECIA 183 

wall or " 

proper margin " round the spore-bearing disc. The branching of 

the hyphae is fastigiate with compact 

shorter branches at the exterior. In 

such an apothecium gonidia are ab- 

sent both below thehypothecium and 

in the margins. 

In lecanorine development the 

ascending hyphae from the medulla, 

in some cases, carry with them algal 

Fig. 10 1. Lecidea parasema Ach. Vertical section 

of thallus and apothecium with proper margin 

only x ca. 50. 

cells which multiply and spread as a second gonidial layer under the hypothecium 

(Fig. 102). These hyphae may also spread in a radial direction 

while still within the thallus and give rise to an " immersed " 

apothecium 

which is lecanorine as it encloses gonidia within its special tissues, for 

example, in Acarospora and Solorina. But in most cases the lecanorine fruit 

is superficial and not unfrequently it is raised on a short stalk (Usnea, etc.); 

Fig. 102. Lecanora far/area Ach. Vertical section of apothecium. 

a, hymenium ; b, proper margin or parathecium ; 

c, thalline margin or amphithecium. x 30 (after Reinke). 

both the primary gonidial zone of the thallus and the outer cortex are asso- 

ciated with the medullary column of hyphae from the first and grow up 

along with it, thus providing the outer part of the apothecium, an additional 

" thalline margin " continuous with the thallus itself. It is an advanced 

type of development peculiar to lichens, and it provides for fertility of long 

continuance which is in striking contrast with the fugitive ascocarps of the 

Discomycetes. 

The distinction between lecideine and lecanorine apothecia is of great 

value in classification, but it is not always easily demonstrable; it is 

occasionally necessary to examine the early stages, as in the more advanced 

disc and become 

the thalline margin may be pushed aside by the turgid 

practically obliterated.

I84 

REPRODUCTION 

The " proper margin " reaches its highest development in the lecideine 

and graphideine types. It is less prominent or often almost entirely replaced 

when the thalline margin is superadded, except in genera such as Thelotrema 

and Diploschistes which have distinct " double margins." 

There is an unusual type of apothecium in the genus Gyrophora. The 

fruit is lecideine, the thalline gonidia taking no part in the development. 

The growth of the initial ascogenous tissue, 

1 

according to Lindau , is constantly towards 

the periphery of the disc so that a weak 

spot arises in the centre which is promptly 

filled by a vigorous sterile growth of para- 

^^^^ , physes. This process is repeated from new 

Fig. 103. Apothecial gyrose discs of r J 

Gyrophora cylindrica. Ach. x 12 (after centres again and again, resulting in the 

Lmdau )irregularly 

concentric lines of sterile and 

fertile areas of the "gyrose" fruit (Fig. 103). The paraphyses soon become 

black at the tips. Asci are not formed until the ascogenous layer has ac- 

quired a certain degree of stability, and spores are accordingly present only 

in advanced stages of growth. 

G. LICHEN ASCI AND SPORES 

a. HISTORICAL. The presence of spores, as such, in the lichen fruit was 

first established by Hedwig 2 in Anaptychia (Physcia) ciliaris. He rightly 

judged the minute bodies to be the "semina" of the plant. In that species 

they are fairly large, measuring about 50 /A long and 24 /j, thick, and as they 

are very dark in colour when mature, they stand out conspicuously from the 

surrounding colourless tissue of the hymenium. Acharius 3 also took note of 

these "semina" and happily replaced the term by that of "spores." They 

may be produced, he states, in a compact nucleus {Sphaerophoron\ in a naked 

disc (Calicium), or they may be embedded in the disc (Opegrapha and'Leadea). 

Sprengel 4 

opined that the spores which he figures were true seeds, though 

he allows that there had been no record of their development into new plants. 

Luyken 5 made a further contribution to the subject by dividing lichens into 

gymnocarpous and angiocarpous forms, according as the spores, enclosed 

in cells or vesicles (thecae), were borne in an open disc or in a closed peri- 

thecium. 

In his Systema of lichen genera Eschweiler 6 

, 

some years later, described 

and figured the spores as " thecae " enclosed in cylindrical asci. FeV in 

contemporary works gave special prominence to the colour and form of the 

spores in all the lichens dealt with. 


5 

Luyken 1809. 

' 

2 

Hedwig 1784. 

6 Eschweiler 1824. 


7 Fee 1824. 

4 Sprengel 1807.

LICHEN ASCI AND SPORES 185 

b. DEVELOPMENT OF THE ASCUS. The first attempt to trace the origin 

and development of lichen asci and spores was made by Mohl 1 . He describes 

the mother-cell (the ascus) as filled at first with a clouded granular sub- 

stance changing later into a definite number usually eight of simple or septate 

spores. Dangeard 2 included the lichens Borrera {Physcia} ciliaris and 

Endocarpon (Dermatocarpon) miniatum among the plants that he studied 

for ascus and spore development. He found that in lichens, as in fungi, the 

ascus arose usually from the penultimate cell of a crooked hypha (Fig. 104) 

and that it contained at first two nuclei 

derived from adjoining cells. These nuclei 

are similar in size to those of the vegetative 

hyphae, and in each there is a large nucleo- 

lus with chromatin material massed on one 

side. Fusion takes place, as in fungi, between 

the two nuclei, and the secondary or definitive 

nucleus thus formed divides suc- 

cessively to form the eight spore-nuclei. 

Baur 3 and Nienburg 4 have confirmed Dangeard's 

results as regards lichens, and Ren 

Maire 5 has also contributed important cyto- 

logical details on the development of the 

spores. In Anaptychia {Physcia) ciliaris he 

found that the fused nucleus became larger 

and that a synapsis stage supervened during 

which the long slender chromatin filaments 

Hi^^lBr ' 

m 

became paired, and at the same time shorter and thicker. The nuclear membrane 

disappeared as the chromatin filaments were united in masses joined 

together by linin threads which also disappeared later. At the most advanced 

stage observed by Maire there was visible a nucleolus embedded in a condensed 

plasma and surrounded by eight medianly constricted filaments 

destined to form the equatorial plate. A few isolated observations were also 

made on the cytology of the ascus in Peltigera canina, in which lichen the 

preceding ascogonial development is wholly vegetative. The secondary 

nucleus was seen to contain a chromatin mass and a large nucleolus; in 

addition two angular bodies of uncertain signification were associated with 

the nucleolus, each with a central vacuole. The nucleolus disappeared in the 

prophase of the first division and four double chromosomes were then plainly 

visible. The succeeding phases of the first and the second nuclear division 

were not seen, but in the prophase of the third it was possible to distinguish 

four chromatin masses outside the nucleolus. The slow growth of the lichen 

plant renders continuous observation extremely difficult. 

1 Mohl 1833. 

2 

Dangeard 1894. 

3 Baur 1904. 

Fig. 104. Developing asci of Physcia 

ciliaris DC. x 800 (after Baur). 

* Nienburg 1908. 

5 Maire 1905.

1 86 

REPRODUCTION 

F. Bachmann 1 was able to make important cytological observations in 

her study of Collema pulposum. As regards the vegetative and ascogonial 

nuclei, five or perhaps six chromosomes appeared on the spindle when the 

nucleus divided. In the asci, the usual paired nuclei were present in the 

early stages and did not fuse until the ascus had elongated considerably. 

After fusion the definitive nucleus enlarged with the growth of the ascus 

and did not divide until the ascus had attained full size. The nucleolus was 

large, and usually excentric, and there were at first a number of chromatin 

masses on an irregular spirem. In synapsis the spirem was drawn into a 

compact mass, but after synapsis, "the chromatin is again in the form of 

a knotty spirem." In late prophases the chromosomes, small ovoid bodies, 

were scattered on the spindle; later they were aggregated in the centre, 

and, in the early metaphase, about twelve were counted now split longitudinally. 

There were thus twice as many chromosomes in the first division 

in the ascus as in nuclear divisions of the vegetative hyphae. F. Bachmann 

failed to see the second division ; 

third division. 

there were at least five chromosomes in the 

Considerable importance is given to the number of the chromosomes in 

the successive divisions in the ascus since they are considered to be proof of 

a previous double fusion in the ascogonium and again in the ascus necessi- 

tating, therefore, a double reduction division to arrive at the gametophytic 

or vegetative number of five or six chromosomes in the third division in the 

ascus. There have been too few observations to draw any general conclusions. 

c. DEVELOPMENT OF SPORES. The spore wall begins to form, as in 

Ascomycetes, at the apex of the nucleus with the curving over of the astral 

threads, the nucleus at that stage presenting the figure of a flask the neck 

of which is occupied by the centrosome. The final spore-nucleus, as observed 

by Maire, divides once again in Anaptychia and division is followed by the 

formation of a median septum, the mature spore being two-celled. In 

Peltigera the spore is at first ovoid, but both nucleus and spore gradually elon- 

gate. The fully formed spore is narrowly fusiform and by repeated nuclear 

division and subsequent cross-septation it becomes 4- or even 5-6-celled. 

The spores of lichens are wholly fungoid, and, in many cases, form a 

parallel series with the spores of the Ascomycetes. Markings of the epispore, 

such as reticulations, spines, etc., are rarely present (Solorina spongiosa), 

though thickening of the wall occurs in many species (Pertusariae, etc.), a 

peculiarity which was first pointed out by Mohl 2 who contrasted the spore 

walls with the delicate membranes of other lichen cells. Some spores, 

described as "halonate," have an outer gelatinous covering which probably 

prevents the spore from drying up and thus prolongs the period of possible 

germination. Both asci and spores are, as a rule, more sparingly produced 


2 Mohl 1833.


than in fungi; in many instances some or all of the spores in the ascus 

are imperfectly formed, and the full complement is frequently lacking, 

possibly owing to some occurrence of adverse conditions during the long 

slow development of the apothecium. In the larger number of genera and 

species the spores are small bodies, but in some, as for instance in the 

Pertusariae and in some Pyrenocarpeae, they exceed in size all known fungus 

spores. In Varicellaria microsticta, a rare crustaceous lichen of high moun- 

tains, the solitary i -septate spore measures up to 350/4 in length and 1 15 /* in 

width. Most spores contain reserve material in the form of fat, etc., many are 

dark-coloured; Zukal 1 has suggested that the colour may be protective. 

Their ejection from the ascus at maturity is caused by the twofold 

pressure of the paraphyses and the marginal hyphae on the addition of 

moisture. The spores may be shot up at least I cm. from the disc 2 . 

d. SPORE GERMINATION. Meyer 3 was the first who cultivated lichen 

spores and the dendritic formation which he obtained by growing them on 

a smooth surface was undoubtedly the prothallus (or hypothallus) of the 

lichen. Actual germination was however not observed till Holle 4 in 1846 

watched and figured the process as it occurs in Physcia ciliaris. 

Spores divided by transverse septa into two or more cells, as well as 

those that have become "muriform" by transverse and longitudinal septation, 

may germinate from each cell. 

e. MuLTINUCLEATE SPORES. These spores, which are all very large, 

occur in several genera or subgenera: in Lecidea subg. Mycoblastus (Fig. 105), 

Lecanora subg. Ochrolechia and in Pertusariaceae. Tulasne 5 in his experi- 

Fig. 105. Multinucleate spore of Lecidea Fig. 106. Germination of multinucleate 

(Mycoblastus) sanguinaria Ach. x 540 spore of Ochrolechia pallescens Koerb. 

(after Zopf). 

x 390 (after de Bary). 

ments with germinating spores found that in Lecanora parella (Ochrolechia 

pallescens^} germinating tubes were produced all over the surface of the 

spore (Fig. 106). De Bary 8 verified his observations in that and other species 

and added considerable detail : about twenty-four hours after sowing spores 

of Ochrolechia pallescens, numerous little warts arose on the surface of the 

1 2 

Zukal 1895. 

Fee 1824. 

* 

Tulasne 1852. 

3 Meyer 1825. 

6 De Bary 1866-1867. 

4 Holle 1849.

i88 

REPRODUCTION 

spore which gradually grew out into delicate hyphae. All these spores 

contain fat globules and finely granular protoplasm with a very large number 

of minute nuclei; the presence of the latter has been demonstrated by 

Haberlandt 1 and later by Zopf 2 who reckoned about 200 to 300 in the 

spore of Mycoblastus sanguinarius. These nuclei had continued to multiply 

during the ripening of the spore while it was still contained in the ascus 2 . 

Owing to the presence of the large fat globules the plasma is confined to 

an external layer close to the spore wall; the nuclei are embedded in the 

plasma and are connected by strands of protoplasm. The epispore in some 

of these large spores is extremely developed: in some Pertusariae it 

measures 4-5 /* in thickness. 

/ POLARIBILOCULAR SPORES. The most peculiar of all lichen spores 

are those termed polaribilocular signifying a two-celled spore of which the 

median septum has become so thickened that the cell-cavities with their 

contents are relegated to the two poles of the spore, an open canal frequently 

connecting the two cell-spaces (Fig. 107). Other terms have been suggested 

and used by various writers to describe this unusual 

3 

character such as blasteniospore orculiform , 4 and 

placodiomorph 5 or more simply polarilocular. 

The polarilocular colourless spore is found in 

a connected series of lichens crustaceous, foliose 

and fruticose (Placodium, Xanthoria, TeloscMstes). 

In another series with a darker thallus (Rinodina 

and Physcia) the spore is brown-coloured, and the 

Fig. 107. Polarilocular spores, median septum cuts across the plasma-connection. 

a, Xanthoria parietina Th. T , , , ... 

Fr. ; b, Kinodina roboris ^ Th. n other respects the brown spore is similar to the 

M r 

1 *" 

V ^My^.Pu! colourless one and possesses a thickened wall with 

Nyl.; d, Physcia cihans DC. 

x6oo. reduced cell-cavities. 

The method of cell-division in these spores resembles that known as 

" 

cleavage by constriction," in which the cross wall arises by an ingrowth 

from all sides of the cell; in time the centre is reached and the wall is com- 

plete, or an open pore is left between the divided cells. Cell "cleavage" 

occurs frequently among Thallophytes, though it is unknown among the 

higher plants. Among Algae it is the normal form of cell-division in Cladophora 

and also in Spirogyra, though in the latter the v/all passes right across 

and.xruts through the connecting plasma threads. Harper 6 found "cleavage 

by constriction " in two instances among fungi : the conidia of Erysiphe and 

the gametes of Sporodinia are cut off by a septum which originates as a 

circular ingrowth of the outer wall, comparable, he considers, with the cell- 

division of Cladophora. 

1 

Haberlandt 2 

a 

1887. Zopf iy)^ 

Massalongo 1852. 

6 Wainio i. 

1890, p. 113. Harper 1899. 

4 Koerber 1855.


The development of the thickened wall of polarilocular spores has been 

studied by Hue 1 

, who 

contends however that there is no true septation in 

the colourless spores so long as the central canal remains open. According 

to his observations the wall of the young spore is formed of a thin tegument, 

everywhere equal in thickness, and consisting of concentric layers. This 

tegument becomes continually thicker at the equator of the spore by the 

addition of new layers from the interior, and the protoplasmic contents are 

compressed into a gradually diminishing space. In the end the wall almost 

touches at the centre, and the spore consists of two polar cell-cavities with 

a narrow open passage between. A median line pierced by the canal is 

frequently seen. In a few species there is a second constriction cleavage 

and the spore becomes quadrilocular. 

Hue insists that this spore should be regarded as only one-celled; for 

though the walls may touch at the centre, he says they never coalesce. He 

has unfortunately given no cytological observations as to whether the spore 

is uni- or binucleate. 

In Xanthoria parietina, one of the species with characteristic polaribilocular 

spores, germination, it would seem, takes place mostly at one end 

only of the spore, though a germinating tube issues at both ends frequently 

enough to suggest that the spore is binucleate and two-celled. The absence 

of germination from one or other of the cells only may probably be due to 

the drain on their small resources. Hue has cited the rarity of such instances 

of double germination in support of his view of the one-celled nature of the 

spore. He instances that out of fifteen spores, Tulasne 2 has figured only 

three that have germinated at each end; Bornet 3 

figures one in seven with 

the double germination and Bonnier 4 one in sixteen spores. 

spores. 

Further evidence is wanted as to the nuclear history of these hyaline 

In the case of the brown spores, which show the same thickening 

of the wall and restricted cell-cavity, though with a distinct median septum, 

nuclear division was observed by Rend Maire 5 before septation in one such 

species, Anaptychia ciliaris. 

II. SECONDARY SPORES 

A. REPRODUCTION BY OIDIA 

In certain conditions of nutrition, fungal hyphae break up into separate 

cells, each of which functions as a reproductive conidium or oidhim, which 

on germination forms new hyphae. Neubner 6 has demonstrated a similar 

process in the hyphae of the Caliciaceae and compares 

formation described by Brefeld 7 in the Basidiomycetes. 

1 2 Hue 1 . 191 

5 Maire 1905. 


6 Neubner 1893. 


it with the oidial 

4 Bonnier i889 2 . 

7 Brefeld 1889.

REPRODUCTION 

The thallus of this family of lichens is granular or furfuraceous ; it never 

goes beyond the Lepra stage of development 1 . In some species it is scanty, 

in others it is abundant and spreads over large areas of the trunks of old 

trees. It is only when growth is especially luxuriant that oidia are formed. 

Neubner was able to recognize the oidial condition by the more opaque 

appearance of the granules, and under the microscope he observed the 

hyphae surrounding the gonidia gradually fall away and break up into 

minute cylindrical cells somewhat like spermatia in size and form. There 

was no question of abnormal or unhealthy conditions, as the oidia were 

formed in a freely fruiting thallus. 

The gonidia associated with the oidial hyphae also showed unusual 

vitality and active division took place as they were set free by the breaking 

up of the encircling hyphae. The germination of the oidia provides an 

abundance of hyphal filaments for the rapidly increasing algal cells, and 

there follows a widespread development of the lichen thallus. 

Oidial formation has not been observed in any other family of lichens. 

B. REPRODUCTION BY CONIDIA 

a. INSTANCES OF CONIDIAL FORMATION. It is remarkable that the 

type of asexual reproduction so abundantly represented in fungi by the large 

Conidia developed 

om thallus of Arnoldia minutula 

Born. x 950 (after 

Bornet). 

and varied group of the Hyphomycetes is practically 

absent in lichens. An exception is to be 

found in a minute gelatinous lichen that grows on 

soil. It was discovered by Bornet 2 and called by 

him Arnoldia (Physmd) minutula. From the thallus 

rise up simple or sparingly branched colourless 

conidiophores which bear at the tips globose brown 

conidia(Fig. 108). Bornet 3 obtained these conidia 

by keeping very thin sections of the thallus in a 

drop of water 2 . 

Yet another instance of conidial growth is given 

by Steiner 4 . He 

had observed that the apothecia 

on plants of Caloplaca aurantia var. callopisma 

Stein, differed from those of normal appearance 

in the warted unevenness of the disc and also in 

being more swollen and convex, the thalline margin 

being almost obliterated. He found, on microscopical 

examination, that the hymenium was 

occupied by paraphyses and by occasional asci, 

the latter seldom containing spores, and being 

See 2 

p. 143. 

Bornet 1873. 

3 

Bornet's observations have not been repeated, and it is possible that he may have been dealing 

with a parasitic hyphomycetous fungus. 

4 Steiner 1901.


usually more or less collapsed. The component parts of the apothecium 

were entirely normal and healthy, but the paraphyses and the few asci were 

crushed aside by the intrusion of numerous slender unbranched septate 

conidiophores. Several of these might spring from one base and the hypha 

from which they originated could be traced some distance into the ascogenous 

layer, though a connection with that cell-system could not be demonstrated. 

While still embedded in the hymenium, an ellipsoid or obovate swelling 

began to form at the apex of the conidiophore; it became separated from 

the stalk by a septum and later divided into a two-celled conidium. 

The conidiophore increased in length by intercalary growth and finally 

emerged above the disc; the mature conidium was pyriform and measured 

1 5-20 /z, x 9-11 yu, 

Steiner regarded these conidia as entirely abnormal; pycnidia with 

stylospores are unknown in the genus and they were not, he alleges, the 

product of any parasitic growth. 

b. COMPARISON WITH HYPHOMYCETES. The conidial form of fructi- 

fication in fungi, known as a Hyphomycete, is generally a stage in the life- 

cycle of some Ascomycete; it represents the rapid summer form of asexual 

reproduction. The ascospore of the resting fruit-form in many species germinates 

on any suitable matrix and may at once produce conidiophores and 

conidia, which in turn germinate, and either continue the conidial generation 

or proceed to the formation of the perfect fruiting form with asci and asco- 

spores. 

Such a form of transient reproduction is almost impossible in lichens, as 

the hypna produced by the germinating lichen ascospore has little vitality 

without the algal symbiont. In natural conditions development practically 

ceases in the absence of symbiosis. When union between the symbionts 

takes place, and growth becomes active, thallus construction at once com- 

mences. But in certain conditions of shade and moisture, only the rudiments 

of a lichen thallus are formed, known as a leprose or sorediose condition. 

Soredia also arise in the normal life of many lichens. As the individual 

granules or soredia may each give rise to a complete lichen plant, they may 

well be considered as replacing the lost conidial fructification. 

C. CAMPYLIDIUM AND ORTHIDIUM 

Mu'ller 1 has described under the name Campy lidium a supposed new type 

of asexual fructification which he found on the thallus of tropical species of 

Gyalecta, Lofadium, etc., and which he considered analogous to pycnidia and 

spermogonia. Wainio 2 has however recognized the cup-like structure as a 

fungus, CypJiella aeruginascens Karst, which grows on the bark of trees and 

occasionally is parasitic on the crustaceous thallus of lichens. Wainio has 

1 Miiller 1881. 

2 Wainio 1890, n. p. 27.

1 9 2 

REPRODUCTION 

also identified the plant, Lecidea irregnlaris, first described by Fe'e 1 

, 

as also 

synonymous with the fungus. 

Another name Orthidium was proposed by M tiller 2 for a type of fructi- 

fication he found in Brazil which he contrasts or associates with Campylidium. 

It has an open marginate disc with sporophores bearing acrogenous spores. 

He found it growing in connection with a thin lichen thallus on leaves and 

considered it to be a form of lichen reproduction. Possibly Orthidium is 

also a Cyphella. 

III. SPERMOGONIA OR PYCNIDIA 

A. HISTORICAL ACCOUNT OF SPERMOGONIA 

The name spermogonium was given by Tulasne 3 to the " 

punctiform 

conceptacles " that are so plentifully produced on many lichen thalli, on the 

assumption that they were the male organs of the plant, and that the spore- 

like bodies borne in them were non-motile male cells or spermatia. 

l 

The first record of their association with lichens was made by Dillenius , 

who indicates the presence of black tubercles on the thallus of Physcia 

dliaris. He figures them also on several species of Cladonia, on Ramalina 

and on Dermatocarpon, but without any suggestion 

as to their function. 

5 Hed wig's study of the reproductive organs of the Linnaean Cryptogams 

included lichens. He examined Physcia dliaris, a species that not only is 

quite common but is generally found in a fruiting condition and with very 

prominent spermogonia,and has been therefore a favourite lichen for purposes 

of examination and study. Hedwig describes and figures not only ^he apo- 

thecia but also those other bodies which he designates as "punctula mascula," 

or again as " 

puncta floris masculi." In his later work he gives a drawing 

of Lichen (Gyrophord) proboscideus, with two of the spermogonia in section. 

Acharius 6 included them among the lichen structures which he called 

" 

cephalodia": he described them as very minute tubercles rising up from 

the substance of the thallus and projecting somewhat above it. He also 

two " 

cephalodia " of Physda dliaris. Fries 7 looked 

figures a section through 

on them as being mostly 

" 

anamorphoses of apothecia, the presence of 

abortive fruits transforming the angiocarpous lichen to the appearance of a 

8 

gymnocarpous form." Wallroth assigned the small black fruits to the com- 

prehensive fungus genus Sphaeria or classified lichens bearing spermogonia 

only as distinct genera and species (Pyrenothea and Thrornbiuni). Later 

students of lichens Schaerer 9 Flotow , 

10 and others , accepted Wallroth's 

interpretation of their relation to the thallus, or they ignored them altogether 

in their descriptions of species. 

1 Fee 1873. 

2 

Miiller 1890. 


* Dillenius 1741. 

*> 

Hedwig 1784 and 1789. 

6 Acharius 1 8 10. 7 Fries 1831. 

8 

Wailroth 1825. 

9 

Schaerer 1823-1842. 

10 Flotow 1850.

SPERMOGONIA 193 

B. SPERMOGONIA AS MALE ORGANS 

Interest in these minute "tubercles" and their enclosed "corpuscles" 

was revived by Itzigsohn 1 who examined them with an improved microscope. 

He macerated in water during a few days that part of the thallus on which 

they were developed, and, at the end of the time, discovered that the 

solution contained large numbers of motile bodies which he naturally took 

to be the corpuscles from the broken down tubercles. He claimed to have 

established their function as male motile cells or spermatozoa. The discovery 

seemed not only to prove their sexual nature, but to link up the reproduction 

of lichens with that of the higher cryptogams. The tubercles in which the 

" 

spermatozoa " were produced he designated as antheridia. More prolonged 

maceration of the tissue to the very verge of decay yielded still larger numbers 

of the " 

spermatozoa " which we now recognize to have been motile bacilli. 

Tulasne 2 next took up the subject, and failing to find the motile cells, 

he wrongly insisted that Itzigsohn had been misled by mere Brownian 

movement, but at the same time he accepted the theory that the minute 

conceptacles were spermogonia or male organs of lichens. He also pointed 

out that their constant occurrence on the thallus of practically every species 

of lichen, and their definite form, though with considerable variation, rendered 

it impossible to regard them as accidental or of no importance to the life of 

the plant. 

He compared them with fungal pycnidia such as Phyllosticta or 

Septoria which outwardly they resembled, but whereas the pycnidial spores 

germinated freely, the spermatia of the spermogonia, as far as his experience 

went, were incapable of germination. 

C. OCCURRENCE AND DISTRIBUTION 

a. RELATION TO THALLUS AND APOTHECIA. We owe to Tulasne 3 the 

first comparative study of lichen spermogonia. He described not only 

their outward form, but their minute structure, in a considerable number 

4 

of representative species. A few years later Lindsay published a memoir 

dealing with the spermogonia of the larger foliose and fruticose lichens, and, 

in a second paper, he embodied the results of his study of an equally ex- 

tensive selection of crustaceous species. Lindsay's work is unfortunately 

somewhat damaged by faulty determination of the lichens he examined, and 

by lack of the necessary discrimination between one thallus and another of 

associated and intermingled species. Both memoirs contain, however, much 

valuable information as to the forms of spermogonia, with their spermatio- 

phores and spermatia, and as to their distribution over the lichen thallus. 

Though spermogonia are mostly found associated with apothecia, yet 

1 


- Tulasne 1851. 


4 

Lindsay 1859 and 1872. 

S. L. 13

194 

REPRODUCTION 

in some lichens, such as Cerania ( Thamnolia) vermicularis, they are the only 

sporiferous organs known. Not unfrequently crustaceous thalli bear spermogonia 

only, and in some Cladoniae, more especially in ascyphous species, 

spermogonia are produced abundantly at the tips of the podetial branches 

(Fig. 109), while apothecia are exceedingly rare. Usually they occur in 

scattered or crowded groups, more rarely they are solitarj'. Very often they 

are developed and the contents dispersed before the apothecia reach the 

surface of the thallus; hence the difficulty in relating these organisms, since 

the mature apothecium is mostly of extreme importance in determining the 

species. 

Fig. 109. C/adomafurcataSchrad. Branched 

podetium with spermogonia at the tips 

. 

(after Krabbe). 

Fig. no. Physcia hispida Tuckerm. Ciliate 

frond, a, spermogonia ; 6, apothecia. x ca. 5 

(after Lindsay). 

In a very large number of lichens, both crustaceous and foliose, the 

spermogonia are scattered over the entire thallus (Fig. 1 10). covering it more 

or less thickly with minute black dots, as in Parmelia conspersa. In other 

instances, they are to some extent confined to the peripheral areas as in 

Parmelia physodes ; or they occur on the extreme edge of the thallus as in 

the crustaceous species Lecanora glaucoma (sordidd). In Pyrenula nitida 

they grow on the marginal hypothallus, usually on the dark line of demarcation 

between two thalli. 

They tend to congregate on, and indeed are practically restricted to the


better lighted portions of the thallus. On the fronds of foliose forms, they 

appear, for instance, on the swollen pustules of Umbilicaria pustulata, while 

in Lobaria pulmonaria, they are mostly lodged in the ridges that surround 

the depressions in the thallus. In Parmelia conspersa, Urceolaria (Diploschistes) 

scruposa and some others, they occasionally invade the margins of 

the apothecium or even the apothecial disc as in Lichina. Forssell 1 found 

that a spermogonium had developed among cells of Gloeocapsa that covered 

the disc of a spent apothecium of Pyrenopsis haematopis. 

In fruticose lichens such as Usnea, Ramalina, etc. they occur near the 

apex of the fronds, and in Cladonia they occupy the tips of the ascyphous 

podetia or the margins of the scyphi. In some Cladoniae, however, spermo- 

gonia are produced on the basal squamules, more rarely on the squamules 

that clothe the podetia. 

b. FORM AND SIZE. Spermogonia are specifically constant in form, the 

same type being found on the same lichen species all over the globe. The 

larger number are entirely immersed and are ovoid or roundish (Fig. 1 1 1 A) 

or occasionally somewhat flattened bodies (Nephromium laevigatum),ov again, 

but more rarely, they are irregular in outline with an infolding of the walls 

that gives the interior a chambered form (Fig. 1 1 1 B) (Lichina pygmaed) ; but 

all of these are only visible as minute points on the thallus. 

Fig. in. Immersed spermogonia. 

B 

A, globose in Parmelia 

acetabulum Dub. x 600 ; B, with infolded walls in Lecidea 

(Psora) testacea Ach. x 144 (after Gliick). 

A second series, also immersed, are borne in small protuberances of the 

thallus. These very prominent forms are rarely found in crustaceous lichens, 

but they are characteristic of such well-known species as Ramalina fraxinea, 

Xanthoria parietina, Ricasolia ampltssima, Baeomyces roseus, etc. Other sper- 

mogonia project slightly above the level of the thallus, as in Cladonia papillaria 

and Lecidea lurida; while in a few instances they are practically free, these 

last strikingly exemplified in Cetraria islandica where they occupy the 

small projections or cilia (Fig. 112) that fringe the margins of the lobes; they 

are free also in most species of Cladonia. 

1 Forssell 1885. 

132

REPRODUCTION 

In size they vary from such minute bodies as those in Parmelia exasperata 

which measure 25-35 p, in diam., up to nearly I mm. in Lobaria laetevirens. 

As a rule, they range from about 150/4 

to 400 across the widest fj, part, and are 

Figj. 112. rree spermogonia in spmous 

cilia of Cetraria islandica Ach. A, part 

of frond; B, cilia, x 10. 

generally rather longer than broad. They 

open above by a small slit or pore called 

the ostiole about 20 yu, to I oo /x wide which 

is frequently dark in colour. In one in- 

stance, in Icmadophila aeruginosa, Nien- 

burg 1 has described a spermogonium with 

a wide opening, the spermatiophores 

being massed in palisade formation along 

the bottom of a cup-like structure. 

c. COLOUR OF SPERMOGONIA. Though 

the ostiole is visible as a darker 

usually 

point than the surrounding tissue, spermogonia 

are often difficult to locate un- 

less the thallus is first wetted, when they become visible to slight magnification. 

They appear as black points in many Parmeliae,Physciae,Roccellae, etc., though 

even in these cases they are often brown when moistened. They are dis- 

tinctly brown in some Cladoniae, in Nephromium, and in some Physciae\ 

orange-red or yellow 

Usnea, Ramalina, Stereocaulon, etc. 

in Placodium and concolorous with the thallus in 

D. STRUCTURE 

a. ORIGIN AND GROWTH. The spermogonia (or pycnidia) of lichens 

when mature are more or less hollow structures provided with a distinct 

wall or " 

perithecium," sometimes only one cell thick and then not easily de- 

monstrable, as in Physcia speciosa, Opegrapha vulgata, Pyrenula nitida, etc. 

More generally the " perithecium " is composed of a layer of several cells 

with stoutish walls which are sometimes colourless, but usually some shade 

of yellow to dark-brown, with a darker ostiole. The latter, a small slit or 

pore, arises by the breaking down of some of the cells at the apex. After 

the expulsion of the spermatia, a new tissue is formed which completely 

blocks up the empty spermogonium. In filamentous lichens such as Usnea 

a dangerous local weakening of the thallus is thus avoided. 

Spermogonia originate from hyphae in or near the gonidial zone. The 

earliest stages have not been seen, but Moller 2 noted as the first recognizable 

appearance or primordium of the "pycnidia" in cultures of Calicium 

trachelinum a ball or coil of delicate yellowish-coloured hyphae. At a more 

1 

Nienburg roo8. 

2 Moller 1887.


advanced stage the sporophores (or spermatiophores) could be traced as 

outgrowths from the peripheral hyphae, directed in palisade formation 

towards the centre of the hyphal coil about 20-30 (j. long and very slender 

and colourless. They begin to bud off spermatia almost immediately, as it 

has been found that these are present in abundance while the developing 

spermogonium is still wholly immersed in the thallus. Meanwhile there is 

gradually formed on the outside a layer of plectenchyma which forms 

the wall. Additional spermatiophores arise from the wall tissue and push 

their way inwards between the ranks of the first formed series. The spermogonium 

slowly enlarges and stretches and as the spermatiophores do not 

grow any longer a central hollow arises which becomes packed with spermatia 

(or spores) before the ostiole is open. 

A somewhat similar process of development is described by Sturgis 1 in 

the spermogonia of Ricasolia amplissima, in which species the primordium 

arises by a profuse branching of the medullary hyphae in certain areas close 

to the gonidial zone. The cells of these branching hyphae are filled with oily 

matter and gradually they build up a dense, somewhat cylindrical body 

which narrows above to a neck-like form. The growth is upwards through 

the gonidial layer, and the structure widens to a more spherical outline. It 

finally reaches the outer cortex when some of the apical cell membranes 

are absorbed and a minute pore is formed. The central part becomes hollow, 

also by absorption, and the space thus left is lined and almost filled with 

multicellular branches of the hyphae forming the wall; from the cells of 

this new tissue the spermatia are abstricted. 

b. FORMS AND TYPES OF SPERMATIOPHORES. The variations in form of 

the fertile hyphae in the spermogonium were first pointed out by Nylanderwho 

described them as 

3 

. sterigmata He considered the differences in 

branching, etc. as of high diagnostic value, dividing them into two groups: 

simple "sterigmata" (or spermatiophores), with non-septate hyphae, and 

arthrosterigmata, with jointed or septate hyphae. 

Simple " 

sterigmata " 

comprise those in which the spore or spermatium is 

borne at the end of a secondary branch or sterigma, the latter having arisen 

from a cell of the upright spermatiophore or from a simple basal cell. The 

arthrosterigmata consist of " short cells almost as broad as they are long, 

much pressed together, and appearing almost agglutinate especially toward 

the base; they fill almost the whole cavity of the spermogonium." The 

arthrosterigmata may grow out into the centre of the cavity as a single 

cell-row, as a loose branching network, or, as in Endocarpon, they may form 

1 

Sturgis 1890. 

2 

Nylander. 1858, pp. 34, 35. 

3 

Nylander, Crombie and others apply the term "sterigma" to the whole spermatiophore. In 

the more usual restricted sense, it refers only to the short process from which the spermatium is 

abstricted.

REPRODUCTION 

a tissue filling the whole interior. Each cell of this tissue that borders on 

a cavity may bud off a spermatium either directly or from the end of a 

short process. 

The most important contributions on the subject of spermogonia in 

recent years are those of Gliick 1 and Steiner 2 . Gliick, who insisted on the 

7 

ig- 1 13 A - Types of lichen " sporophores " and i , 

pycnidiospores. 

Pdtigera rufescens fioffm. x 910; 2, Lecidea (Psora) testacea Ach. 

x 1200; 3, Cladonia cariosa Spreng. x 1000; 4, Pyrenula nitida 

Ach. x 1130; 5, Parmelia trtstis Nyl. x 700; 6, Lobaria pulmonaria 

Hoffm. x jooo (after Gliick). 

1 Gluck 1899., 

2 Steiner 1901.


"pycnidial" non-sexual character of the organs, recognized eight types of 

"sporophores" differing in the complexity of their branching or in the form 

of the "spores" (Fig. 1 13 A): 

1. The Peltigera type: the sporophores consist of a basal cell bearing 

one or more long sterigmata and rather stoutish ellipsoid spores. (These 

are true pycnidia.) 

2. The Psora type: a more elongate simple sporophore with sterigmata 

and oblong spores. 

3. The Cladonia type: a branching sporophore, each branch with sterigmata 

and oblong spores. 

4. The Squamaria type (called by Gliick Placodiuni) : also a branching 

sporophore but with long sickle-like bent spores. 

5. The Parmelia type: a more complicated system of branching and 

anastomosing of the sporophores, with oblong spores. 

6. and 7. The Sticta and Physcia types: in both of these the sporo- 

phores are multiseptate; they consist of a series of radiately arranged 

hyphae rising from a basal tissue all round the pycnidium. They anastomose 

to form a network and bud off " 

spermatia " from the free cells or 

rather from minute sterigmata. In the Physcia type there is more general 

anastomosis of the sporophores and frequently masses of sterile cells along 

with the fertile members occupy the centre of the pycnidium. The sper- 

matia of these and the following Endocarpon type are short cylindrical 

bodies (Fig.- 1138). 

7 

Fig. 1136. 7, Physcia ciliaris DC. x 600; 8, Endocarpon sp. 

x 600 

(after Gliick). 

8. Endocarpon type: the pycnidium is filled by a tissue of short broad 

cells, with irregular hollow spaces lined by fertile cells similar to those of 

the Sticta and Physcia types.

200 

REPRODUCTION 

The three last named types of sporophores represent Nylander's section 

of arthrosterigmata. Steiner has followed Nylander in also arranging the 

various forms into two leading groups. The first, characterized by the 

secondary branch or "sterigma," he designates "exobasidial"; the second, 

comprising the three last types in which the spores are borne directly on 

the cells of the sporophore or on very short processes, he describes as " endo- 

basidial." Steiner also introduces a new term, fulcrum for the > sporophore. 

The pycnidia in which these different sporophores occur are not, as a 

rule, characteristic of one family. Peltigera type is found only in one family 

and the Cladonia type is fairly constant in Cladoniae, but "Psora" pycnidia 

are found on very varying lichens among the Lecideaceae, Verrucariaceae 

and others. The Squamaria type with long bent spores is found not only in 

Squamaria (Gliick's Placodium) but also in Lecidea, Roccella, Pyrenula, etc. 

Parmelia type is characteristic of many Parmeliae and also of species of 

Evernia, Alectoria, Platysma and Cetraria. The Sticta type occurs in Gyrophora, 

Umbilicaria, Nephromium and Lecanora as well as in Sticta and in one 

species at least of Collema. To the Physcia type belong the pycnidia of most 

Physciaceae and of various Parmeliae, and to the closely related Rndocarpon 

type the pycnidia of Endocarpon and of Xanthoria parietina. 

c. PERIPHYSES AND STERILE FILAMENTS. In a few species, Roccella 

tinctoria,Pertusariaglobulifera,&\ic.,shor\. one-celled sterile hyphae are formed 

within the spermogonium near the ostiole, towards which they converge. 

. 4 Sterile filaments in 

They correspond to the periphyses in the perithecia 

of some Pyrenolichens, Verrucaria, etc. 

(described by Gibelli 1 as spermatiophores); they 

are also present in some of the Pyrenomycetes 

(Sordaria, etc.), and in many cases replace the 

paraphyses in function when these have broken 

down. Sterile hyphae also occur, towards the base, 

mingled with the fertile spermatiophores (Fig. 

114). These latter were first described and SS5ST mLh'mfgnified 

figured 

b7 Tulasne 2 in the spermogonia of Ramalina 

(after Lindsay). fraxinea as stoutish branching filaments, rising 

from the same base as the spermatiophores but much longer, and frequently 

anastomosing with each other. They have been noted also in Usnea barbata 

and in several species of Parmelia, and have been compared by Ny- 

lander 3 to paraphyses. They are usually colourless, but, in the Parmeliae, 

are often brownish and thus easily distinguished from the spermatiophores. 

It has been stated that these filaments are sometimes fertile. Similar 

sterile hyphae have been recorded in the pycnidia of fungi, in Sporocladus 

(Hendersonia) lichenicola (Sphaeropsideae) by Corda 4 who described them as 

1 Gibelli 1866. 



4 Corda 1839.


paraphyses, and also in Steganosporium cellulosum (Melanconieae). These 

observations have been confirmed by Allescher 1 in his recent work on Fungi 

Imperfecti. Keiszler 2 has described a P/wma-\ike pycnidium parasitic on 

the leprose thallus of Haematomma elatinum. It contains short slender 

sporophores and, mixed with these, long branched sterile hyphae which 

reach to the ostiole and evidently function as paraphyses, though Keiszler 

suggests that they may be a second form of sporophore that has become 

sterile. On account of their presence he placed the fungus in a new genus 

L icJienophoma. 

E. SPERMATIA OR PYCNIDIOSPORES 

a. ORIGIN AND FORM OF SPERMATIA. Lichen spermatia arise at the 

tips of the sterigmata either through simple abstriction or by budding. In 

the former case as in the Squamaria type a delicate cross-wall is formed 

by which the spermatium is separated off. When they arise by budding, 

there is first a small clavate sac r like swelling of the end of the short process or 

sterigma which gradually grows out into a spermatium on a very narrow base. 

This latter formation occurs in the Sticta, Physcia and Endocarpon types. 

Ny lander 3 has distinguished the following forms of spermatia: 

1. Ob-clavate, the ^road end attached to the sterigma as in Usneae, 

Cetraria glauca and C. juniperina. 

2. Acicular and minute but slightly swollen at each end, somewhat 

dumb-bell like, in Cetraria nivalis, C. cucullata, Alectoria, Evernia and some 

Parmeliae, frequently borne on "arthrosterigmata." 

3. Acicular, cylindrical and straight, the most common form ; these occur 

in most of the Lecanorae, Cladoniae, Lecideae, Graphideae, Pyrenocarpeae 

and occasionally they are budded off from arthrosterigmata. 

4. Acicular, cylindrical, bent; sometimes these are very long, measuring 

up to 40 //.; they are found in various Lecideae, Lecanorae, Graphideae, 

Pyrenocarpeae, and also in Roccella, Pilophorus and species of Stereocaulon. 

5. Ellipsoid or oblong and generally very minute; they are borne on 

simple sterigmata and are characteristic of the genera Calicium, Chaenotheca, 

Lichina,Ephebe,ofi\\e. small genus Glypholecia and of a few species tfLecanora 

and Lecidea. 

In many instances there is more or less variation of form and of size in 

the species or even in the individual. There are no spherical spermatia. 

b. SIZE AND STRUCTURE. The shortest spermatia in any of our British 

lichens are those of Lichina pygmaea which are about i'4/A in length and 

In width 

the longest are those of Lecanora crassa which measure up to 39 ft. 

they vary from about O'5/tt to 2/z. The mature is filled spermogonium with 

1 Allescher 1901-3. 

2 Keiszler 1911. 

3 Nylander 1858, p. 37-

202 

REPRODUCTION 

spermatia and, generally, with a mass of mucilage that swells with moisture 

and secures their expulsion. 

The spermatia of lichens are colourless and are provided with a cell-wall 

and a nucleus. The presence of a nucleus was demonstrated by Holier 1 in 

the spermatia of Calicium parietinum, Opegrapha atra, Collema micropkyllum, 

C.pulposum and C. Hildenbrandii, and by Istvanffi 2 in those of Buellia punctiformis 

(B. myriocarpa), Opegrapha subsiderella, Collema Hildenbrandii, Calicium 

trachelinum,Pertusaria communis andArt&oma communis (A. astroided). 

Istvanffi made use of fresh material, fixing the spermatia with osmic acid, 

and in all of these very minute bodies he demonstrated the presence of a 

nucleus which stained readily with haematoxylin and which he has figured 

in the spermatia of Buellia punctiformis as an extremely small dot-like 

structure in the centre of the cell. On germination, as in the cell-multi- 

plication of other plants, the nucleus leads the way. Germination is preceded 

by nuclear division, and each new hyphal cell of the growing mycelium 

receives a nucleus. 

c. GERMINATION OF SPERMATIA (pycnidiospores). The strongest argu- 

ment in favour of regarding the spermatia of lichens as male cells had always 

been the impossibility of inducing their germination. That difficulty had at 

length been overcome by Moller 1 who cultivated them in artificial solutions, 

and by that means obtained germination in nine different lichen species. 

He therefore rejected the commonly employed terms spermatia and spermogonia 

and substituted pycnoconidium and pycnidia. Pycnidiospore has 

been however preferred as more in accordance with modern fungal termi- 

nology. His first experiment was with the "spermatia" of Buellia punctiformis 

(B. myriocarpa) which measure about 8-10/1. in length and about 3 ^ in 

width, and are borne directly on the septate spermatiophores (arthrosterigmata). 

In a culture drop, the spore had swelled to about double its size by 

the second or third day, and germination had taken place at both ends, the 

membrane of the spore being continuous with that of the germinating tube. 

In a short time cross septa were formed in the hyphae which at first were 

very close to each other. While apical growth advanced these first formed 

cells increased in width to twice the original size and, in consequence, became 

slightly constricted at the septa. In fourteen days a circular patch of mycelium 

had been formed about 280/1 in diameter. The development exactly 

resembled that obtained from the ascospores of the same species grown in the 

absence of gonidia. The largest thallus obtained in either case was about 

2mm. in diameter after three months' growth. The older hyphae had a 

tendency to become brownish in colour; those at the periphery remained 

colourless. In Opegrapha subsiderella the development, though equally 

1 Moller 1887. 

2 Istvanffi 1895.


successful, was very much slower. The pycnidiospores (or spermatia) have 

the form of minute bent rods measuring 57 /t x 1-5 /i. 

Each end of the spore 

produced slender hyphae about the fifth or sixth day after sowing. In four 

weeks, the whole length of the filament with the spore in the middle was 

300/1. In four months a patch of mycelium was formed 2 mm. in diameter. 

Growth was even more sluggish with the pycnidiospores of Opegrapha atra. 

In that species they are rod-shaped and 5-6/4 long. Germination took place on 

the fifth or sixth day and in fourteen days a germination tube was produced 

about five times the length of the spore. In four weeks the first branching 

was noticed and was followed by a second branching in the seventh week. 

In three months the mycelial growth measured 200-300/4 across. 

Germination was also observed in a species of Arthonia, the spores of 

which had begun to grow while still in the pycnidium. The most complete 

results were obtained in species of Calicium : in C. parietinum the spores, 

which are ovoid, slightly bent, and brownish in colour, swelled to an almost 

globose shape and then germinated by a minute point at the junction of spore 

and sterigma, and also at the opposite end; very rarely a third germinating 

tube was formed. Growth was fairly rapid, so that in four weeks there was 

a loose felt of mycelium measuring about 2 cm. x i cm. and I mm. in depth. 

Parallel cultures were carried out with the ascospores and the results in both 

cases were the same; in five or six weeks small black points appeared, which 

gradually developed to pycnidia with mature pycnidiospores from which 

further cultures were obtained. 

On C. trachelinum, which has a thin greyish-white thallus spreading over 

old trunks of trees, the pycnidia are usually abundant. Lindsay had noted 

two different kinds and his observation was confirmed by Moller. The 

spores in one pycnidium are ovoid, measuring 2-5-3 /u, x J'S" 2 ^; m tne 

other rarer form, they are rod-shaped and 5~7/t long. In the artificial 

cultures they both swelled, the rod-like spores to double their width before 

germination, and sometimes several tubes were put forth. Growth was slow, 

but of exactly the same kind from these two types of spores as from the 

ascospores. At the end of the second month pycnidia appeared on all the 

cultures, in each case producing the ovoid type of spore. 

In a second paper Moller 1 recorded the partially successful germination 

of the "spermatia" of Collema (Leptogium) microphyllum, the species in which 

Stahl had demonstrated sexual reproduction. Growth was extraordinarily 

slow : after a month in the culture solution the first swelling of the spermatium 

prior to germination took place, and some time later small processes 

were formed in two or three directions. In the fourth month a branched 

filament was formed. 

Moller's experiments with ascospores and pycnidiospores were primarily 

1 Moller 1888.

204 

REPRODUCTION 

undertaken to prove that the lichen hyphae were purely fungal and parasitic 

on the algae. A series of cultures were made by Hedlund 1 in order to 

demonstrate that the pycnidiospores were asexual reproductive bodies ; 

they were grown in association with the lichen alga and their germination 

was followed up to the subsequent formation of a lichen thallus. 

d. VARIATION IN PYCNIDIA. On the thallus of Catillaria denigrata 

(Biatorina synothed) Hedlund found that there were constantly present two 

types of pycnidia: the one with short slightly bent spores 4-8 yu, x 1*5 //,, the 

other with much longer bent spores 10-20 ft x 1-5 p; there. were numerous 

transition forms between the two kinds of spores. Germination took place 

the hypha produced became septate and 

by the prolongation of the spore ; 

branches were soon formed. Hedlund found that frequently germination 

had already begun in the spores expelled from the spermogonium. In newly 

formed thalline areolae it was possible to trace back the mycelium to innu- 

merable germinating spores of both types, long and short. 

Lindsay had recorded more than one form of spermogonium on the 

same lichen thallus, the spermatia varying considerably in size; but he was 

most probably dealing with the mixed growth of more than one species. 

The observations of Moller and Hedlund on this point are more exact, but 

the limits of variation would very well include the two forms found by 

Moller in Calicium tradielinum ; and in the different pycnidia of Catillaria 

denigrata Hedlund not only observed transition stages between the two 

kinds of spores, but the longer pycnidiospores, as he himself allows, indicated 

the elongation prior to germination : there is no good 

one form in any species. 

F. PYCNIDIA WITH MACROSPORES 

evidence of more than 

Tulasne 2 records the presence on the lichen thallus of "pycnidia" as 

well as of "spermogonia"; the former producing stylospores, larger bodies 

than spermatia, occasionally septate and containing oil-drops or guttulae. 

These spores are pyriform or ovoid in shape and are always borne at the 

tips of simple sporophores. He compared the pycnidia with the 

genera Cytospora, Septoria, 

fungus 

etc. As a rule they occur on lichens with a 

poorly developed thallus, on some species of Lecanora, Lecanactis, Cali- 

cium, Porina, in the family Strigulaceae and in Peltigera. 

There is no morphological difference between pycnidia and spermogonia 

except that the spermatia of the latter are narrower ; but the difference is 

so slight that, as Steiner has pointed out, these organs found on Lecanora 

piniperda, L. Sambuci and L. effusa have been described at one time as 

containing microconidia (spermatia), at another macroconidia (stylospores). 

1 Hedlund 1892. 

2 Tulasne 1852.


He also regards as macrospores those of the pycnidia of Calicium tra- 

chelinum which Moller was able to germinate so successfully, and all the 

more so as they were brownish in colour, true microspores or spermatia 

being colourless. 

Miiller 1 has recorded some observations on the pycnidia and stylospores 

of the Strigulaceae, a family of tropical lichens inhabiting the leaves of 

the higher plants. On the thallus of Strigula elegans var. tremula from 

Madagascar and from India, he found pycnidia with stylospores of abnormal 

dimensions measuring 18-26/4 in length and 3 /A in width, and with I to 7 

cross septa. In Strigula complanata var. genuina the stylospores were 2-8- 

septate and varied from 7-65 /* in length, some of the spores being thus 

ten times longer than others, while the width remained the same. Miiller 

considers that in these cases the stylospore has already grown to a septate 

hypha while in the pycnidium. As in the pycnidiospores, described later 

by Hedlund, the spores had germinated by increase in length followed by 

septation. 

The spermogonia of Strigula, which are exactly similar to the pycnidia 

in size and structure, produce spermatia, measuring about 3/4 x 2/*, and it is 

suggested by Miiller that the stylospores may represent merely an advanced 

stage of development of these spermatia. Both organs were constantly 

associated on the same thallus ; but whereas the spermogonia were abundant 

on the younger part of the thallus at the periphery, they were almost 

entirely replaced by pycnidia on the older portions near the centre, only 

a very few spermogonia (presumably younger pycnidial stages) being found 

in that region. 

Lindsay 2 has described a great many different lichen pycnidia, but in 

many instances he must have been dealing with species of the "Fungi imperfecti" 

that were growing in association with the scattered granules of 

crustaceous lichens. There are many fungi Discomycetes and Pyreno- 

mycetes parasitic on lichen thalli, and he has, in some cases, undoubtedly 

been describing their secondary pycnidial form of fruit, which indeed may 

appear far more frequently than the more perfect ascigerous form, and might 

easily be mistaken for the pycnidial fructification of the lichen. 

G. GENERAL SURVEY 

a. SEXUAL OR ASEXUAL. It has been necessary to give the preceding 

detailed account of these various structures pycnidia or spermogonia in 

view of the extreme importance attached to them as the possible male 

organs of the lichen plant, and, in giving the results obtained by different 

workers, the terminology employed by each one has been adopted as far as 

1 Miiller 1885. 

2 

Lindsay 1859 and 1872.

2o6 

REPRODUCTION 

possible: those who consider them to be sexual structures call them spermogonia 

; those who refuse to accept that view write of them as pycnidia. 

Tulasne, Nylander and others unhesitatingly accepted them as male 

organs without any knowledge of the female cell or of any method of ferti- 

lization. Stahl's discovery of the trichogyne seemed to settle the whole 

question ; but though he had evidence of copulation between the spermatium 

and the receptive cell or trichogyne he had no real record of any sexual 

process. 

Many modern lichenologists reject the view that they are sexual; they 

regard them as secondary organs of fructification analogous to the pycnidia 

so abundant in the related groups of fungi. One would naturally expect 

these pycnidia to reappear in lichens, and it might be considered somewhat 

arbitrary to classify pycnidia in Sphaeropsideae as asexual reproductive 

organs, and then to regard the very similar structures in lichens as sexual 

spermogonia. It has also been pointed out that when undoubted pycnidia 

do occur on the lichen thallus, as in Calicium, Strigula, Peltigera, etc., they 

in no way differ from structures regarded as spermogonia except in the size 

of the pycnidiospores and, even among these, there are transition forms. 

The different types of spermatia can be paralleled among the fungal pyc- 

nidiospores and the same is also true as regards the sporophores generally. 

Those described as arthrosterigmata by Nylander as endosporous by 

Steiner were supposed to be peculiar to lichens; but recently Laubert 1 has 

described a fungal pycnidium which grew on the trunk of an apple tree and 

in which the spores are not borne on upright sporophores but are budded 

off from the cells of the plectenchyma lining the pycnidium. It may be that 

future research will discover other such instances, though that type of sporo- 

phore is evidently of very rare occurrence among fungi. 

b. COMPARISON WITH FUNGI. The most obvious spermogonia among 

fungi with which to compare those of lichens occur in the Uredineae where 

they are associated with the life-cycle of a large number of rust species. 

They are small flask-shaped structures very much like the simpler forms of 

pycnidia and they produce innumerable spermatia which are budded off from 

the tips of simple spermatiophores. The mature spermatium has a delicate 

cell-wall and contains a thin layer of cytoplasm with a dense nucleus which 

occupies almost the whole cavity, cytological characters which, as Blackman 2 

has pointed out, are characteristic of male cells and are not found in any 

asexual reproductive spores. If we accept Istvanm's 3 

description and figures 

of the lichen spermatia as correct, their structure is wholly different : there 

being a very small nucleus in the centre of the cell comparable in size with 

those of the vegetative hyphae (Fig. 1 15). 

1 Laubert 1911. 

2 Blackman 1904. 

3 Istvanffi 1895.


Lichen " 

spermatia " also differ very strikingly from the male cells of any 

given group of plants in their very great diversity of form and size; but the 

a 

Fig. 115. a, spermatia; b, hypha produced from spermatium of 

Buellia punctiformis Th. Fr. XQSO (after Istvanffi). 

chief argument adduced by the opponents of the sexual theory is the capacity 

of germination that has been proved to exist in a fair number of species. It 

is true that germination has been induced in the spermatia of the Uredines by 

several research workers by Plowright 1 

, Sappin-Trouffy 2 and by Brefeld 3 

who employed artificial nutritive solutions (sugar or honey), but the results 

obtained were not much more than the budding process of yeast cells. Bre- 

feld also succeeded in germinating the " spermatia " of a pyrenomycetous 

fungus, Polystigma rubntm, one of the germinating tubes reaching a length 

four times that of the spore; but it is now known that all of these fungal 

spermatia are non-functional, either sexually or asexually, and degenerate 

soon after their expulsion, or even while still in the spermogonium. 

c. INFLUENCE OF SYMBIOSIS. In any consideration of lichens it is 

constantly necessary to hark back to their origin as symbiotic organisms, 

and to bear in mind the influence of the composite life on their development. 

After germination from the spore, the lichen hypha is so dependant on its 

association with the alga, that, in natural conditions, though it persists 

without the gonidia for a time, it attains to only a rather feeble growth of 

mycelial filaments. In nutritive cultures, as Moller has proved, the absence 

of the alga is partly compensated by the artificial food supply, and a scanty 

thalline growth is formed up to the stage of pycnidial fruits. Not only in 

pycnidia but in all the fruiting bodies of lichens, symbiosis has entailed 

a distinct retrogression in the reproductive importance of the spores, as 

compared with fungi. 

In Ascomycetes, the asci constitute the overwhelming bulk of the 

hymenium ; 

in most lichens, there are serried ranks of paraphyses with 

comparatively few asci, and the spores are often imperfectly developed. 

It would not therefore be if surprising the bodies claimed by Moller and 

others as pycnidiospores had also lost even to a considerable extent their 

reproductive capacity. 

1 Plowright 1889. 

2 

Sappin-Trouffy 1896. 

3 Brefeld 1891.

208 REPRODUCTION 

d. VALUE IN DIAGNOSIS. Lichen spermpgonia have once and again 

been found of value in deciding the affinity of related plants, and though 

there are a number of lichens in which we have no record of their occurrence, 

they are so constant in others, that they cannot be ignored in any true 

estimation of species. Nylander laid undue stress on spermogonial characters, 

considering them of almost higher diagnostic value than the much more 

important ascosporous fruit. They are, after all, subsidiary organs, and 

often especially in crustaceous species they are absent, or their relation 

to the species under examination is doubtful.

CHAPTER V 

PHYSIOLOGY 

I. CELLS AND CELL PRODUCTS 

ANY study of cells or cell- membranes in lichens should naturally include 

those of both symbionts, but the algae though modified have not been 

profoundly changed, and their response to the influences of the symbiotic 

environment has been already described in the discussion of lichen gonidia. 

The description of cells and their contents refers therefore mainly to the 

fungal tissues which form the framework of the plant ; they have been 

transformed by symbiosis to lichenoid hyphae in some respects differing 

from, in others resembling, the fungal hyphae from which they are derived. 

A. CELL-MEMBRANES 

a. CHITIN. It was recognized by workers in the early years of the 

nineteenth century that the substance forming the cell-walls of fungal 

hyphae differed very markedly from the cellulose of the membranes in other 

groups of plants, the blue colouration with iodine and sulphuric acid so 

characteristic of cellulose being absent in most fungi. Various explanations 

were suggested ; but it was always held that the doubtful substance was a 

cellulose containing something peculiar to fungi, this view being strengthened 

by the fact that, after long treatment with potash, a blue reaction was 

obtained. It was called fungus-cellulose by De Bary 1 in order to distinguish 

it from true cellulose. 

It was not till a much later date that any exact work was done on the 

fungal cell, and that Gilson 2 

by his researches was able to prove that the 

membranes of fungi contained probably no cellulose, or, "if cellulose were 

present, it was in a different condition from the cellulose of other plants." 

Winterstein 3 followed with the results of his examination of fungus-cellulose: 

he found that it contained nitrogen and therefore differed very considerably 

from typical plant cellulose. Gilson 4 

published a second paper dealing 

entirely with fungal tissues in which he also established the presence of 

nitrogen, and added that this nitrogenous compound resembled in various 

ways the chitin 8 of animal cells. He further discovered that by heating it 

with potash a substance was obtained that took a reddish-violet stain when 

treated with* iodine and weak sulphuric acid. This substance, called by him 

mycosin, was proved 

later to be similar to chitosan 5 

, 

a product of chitin. 

1 2 3 4 De Bary 1866, p. 7. Gilson 1893. 

Winterstein 1893. Gilson 1894. 

5 The chemical formula of chitin \ given as CaoHiooNgOas, that of chitosan as CuH^NaOio- 

S. L. 14

210 

Escombe 1 

PHYSIOLOGY 

analysed the hyphal membranes of Cetraria and found that 

they consisted mainly of a body called by him lichenin and of a para- 

galactan. From Peltigera he extracted a substance with physical properties 

agreeing fairly well with those of chitosan, though analysis did not give 

percentages reconcilable with that substance; the yield however was very 

small. No lichenin was detected. 

Van Wisselingh 2 examined the hyphae of lichens as well as of fungi and 

experimented with a considerable number of both types of plants. He 

succeeded in proving the presence of chitin in the higher fungi (Basidio- 

mycetes and Ascomycetes) and in lichens with one or two exceptions 

found was exceed- 

. (Cladonia and Cetraria}. Though in some the quantity 

ingly small, in others, such as Peltigera, the walls of the hyphae were 

extremely chitinous. More recently Wester 3 has gone into the question as 

regards lichens, and he has practically confirmed all the results previously 

obtained by Wisselingh. In some species, as for instance in Cladonia rangiferina, 

Cl. squamosa, Cl. gracilis, Ramalina calicaris, Solorina crocea and 

others, he found that chitin existed in large quantities, while in Evernia 

prunastri, Usnea florida, U. artiailata, Sticta damaecornis and Parmelia 

saxatilis very little was present. The variation in the amount present may 

be very great even in the species of one genus : none for instance has been 

detected in Cetraria islandica nor in C. nivalis while it is abundant in other 

Cetrariae. There is also considerable variation in quantity in different 

individuals of the same species, and even in different parts of the thallus 

of one lichen. Factors such as habitat, age of the plant, etc., may, however, 

account to a considerable extent for the differences in the results obtained. 

b. LICHENIN AND ALLIED CARBOHYDRATES. It has been proved, as 

already stated, that chitin is present in the hyphal cell-walls of all the lichens 

examined except in those of Cetraria islandica (Iceland Moss), C. nivalis 

to Wester 3 

and, according 

lichens another substance of purely carbohydrate nature is the chief consti- 

, in those of Bryopogon (Alectoriae). In these 

tuent of the cell-walls which swell up when soaked in water to a colourless 

gelatinous substance. 

Berzelius 4 

first drew attention to the peculiar qualities of this lichen 

product, and, recognizing its resemblance in many respects to ordinary starch, 

he called it " lichen-starch " or " moss-starch." More exact observations were 

made later by Guerin-Varry 5 who described its properties and showed by 

his experiments that it contained no admixture of either starch or gum. He 

adopted the name lichenin for this organic soluble part of Iceland Moss. 

An analysis of lichenin was made by Mulder 6 who detected in addition to 

lichenin, which coloured yellow with iodine, small quantities of a blue- 

1 Escombe 2 

1896. Wisselingh 1898 

5 

Guerin-Varry 1834. 

3 Wester 1909. 

s Mulder 1838. 

4 Berzelius 1813.

CELLS AND CELL PRODUCTS 211 

colouring substance which could be dissolved out from the lichenin and 

which he considered to be true starch. Berg 1 also demonstrated the com- 

pound nature of lichenin: he isolated two isomerous substances with the 

formula C 6 H 10 O 5 . The 

name " isolichenin " was given to the second blue- 

colouring substance by Beilstein 2 in 1881. 

More recently Escombe 3 has chemically analysed the cell-wall of Cetraria 

islandica: after the elimination of fat, oil, colouring matter and bitter consti- 

tuents he found that there remained the compound lichenin, an anhydride of 

as stated above, consists of two 

galactose with the formula C 6 H 10 O 5 , which, 

substances lichenin and isolichenin 4 

; the latter is soluble in cold water and 

gives a blue reaction with iodine, lichenin is only soluble in hot water and is 

not coloured blue. Both are derivatives of galactose, a sugar found in a great 

number of organic tissues and substances, among others in gums. 

Lichenin has also been obtained by Lacour 5 from Lecanora esculenta, an 

edible desert lichen supposed to be the manna of the Israelites. Wisselingh 6 

tested the hymenium of thirteen different lichens for lichenin. He found it 

in the walls of the ascus of all those he examined except Graphis. Everniin, 

a constituent of Evernia prunastri, was isolated and described by Stude 7 . 

It is soluble in water and, though considered by Czapek 8 to be identical 

with lichenin, it differs, according to Ulander", in being dextro-rotatory to 

polarized light; lichenin on the contrary is optically inactive. 

3 Escombe 

also obtained a substance from Evernia which he considered to be comparable 

with chitosan. Usnein which has been extracted 6 from Usnea barbata 

may also be identical with lichenin, but that has not yet been established. 

Ulander 9 examined chemically the cell-walls of a fairly large number of 

lichens. Cetraria islandica, C. aculeata and Usnea barbata, designated as 

the " Cetraria group," contained soluble mucilage-forming substances similar 

to lichenin. A second " Cladonia group " which included Cl. rangiferina 

with the variety alpestris, Stereocaulonpaschale and Peltigera aphthosa yielded 

almost none. After the soluble carbohydrates were removed by hot water, 

the insoluble substances were hydrolysed and the "Cetraria group" was found 

to contain abundant d-glucose with small quantities of d-mannose and 

d-galactose; the "Cladonia group," abundant d-mannose and d-galactose with 

but little d-glucose. Hydrolysis was easier and quicker with the former group 

than with the latter. 

Besides these, which rank as hexosans, Ulander found small quantities 

of pentosans and methyl pentosans. All these substances which are such 

important constituents of the hyphal membranes of lichens are classed by 

Ulander as hemicelluloses of the same nature as mannan, galactan and dex- 

tran, or as substances between hemicellulose and the glucoses represented 

1 

Berg 1873. 

5 Lacour 1880. 

- Beilstein ex Errera 1882, p. 16 (note). 

6 

Wisselingh 1898. 

7 Stude 1864. 

3 Escombe 1896. 

8 Czapek 1905, I. p. 515. 

4 Wiesner 1900. 

9 Ulander 1905. 

142

212 

PHYSIOLOGY 

by lichenin, everniin, etc. They are doubtless reserve stores of food material, 

and they are chiefly located in the cell-walls of the medullary hyphae which 

are often so thick as almost to obliterate the lumen of the cells. Ulander 

made no test for chitin in his researches. 

Ulander's results have been confirmed by those obtained by K. Miiller 1 . 

In Cladonia rangiferina, Muller found that the cell-membranes of the hyphae 

contained, as hemicelluloses, pentosans in small quantities and galactan, but 

no lichenin and very little chitin. In Evernia prunastri hemicelluloses formed 

the chief constituents of the thallus, and from it he was able to isolate 

galactan soluble in weak hot acid, and everniin soluble in hot water, the 

latter with the formula C 7 Hi 5 O 6 , a result differing from that obtained by 

Stiide 2 who has given it as C 9 H 14 O 7 ; chitin was also present in small 

quantities. In Ramalina fraxinea, the soluble part of the thallus (in hot 

water) differed from everniin and might probably be lichenin. Cetraria 

islandica was also analysed and yielded various hemicelluloses, chiefly 

dextran and galactan, with less pentosan. No chitin has ever been found in 

this lichen. In testing minute quantities of material for chitin, Wisselingh 3 

heated the tissue in potash to i6oC. The potash was then gradually re- 

placed by glycerine and distilled water; the precipitate was placed on a slide 

and the preparation stained under the microscope by potassium-iodide-iodine 

and weak sulphuric acid. Chitin, if present, would have been changed by 

the potash to mycosin which gives a violet colour with the staining solution. 

It has been stated by Schellenberg 4 that these lichen membranes may 

become lignified. He obtained a red reaction with phloroglucine test 

for lignin in Cetraria islandica and Cladonia furcata. Further research is 

required. 

c. CELLULOSE. Several workers claim to have found true cellulose in 

the cell-walls of the hyphal tissues of a few lichens ; but the more careful 

5 

of Escombe Wisselingh 3 and Wester 6 have disproved their results. 

analyses 

The cell-walls of all the gonidia, however, are formed of cellulose, or according 

to Escombe of glauco-cellulose, except those of Peltigera in which Wester 

found neither cellulose nor chitin. Czapek 7 

suggests that the blue reaction 

with iodine characteristic of the cell-walls in some apothecia, of the asci and 

of the hyphae in cortex or medulla in a few instances, may be due to the 

presence of carbohydrates of the nature of galactose. Moreau 8 in a recent 

paper terms the substance that gives a blue reaction with iodine at the tips 

of the asci " 

amyloid." In Peltigera the ascus tip is occupied by such a plug 

of amyloid which at maturity is projected like a cork from the ascus and 

may be found on the surface of the hymenium. 

1 Muller 1905. 

5 Escombe 1896. 

2 Stude 1864. 

6 Wester 1909. 

3 

Wisselingh 1898. 

7 

Czapek 1905, I. p. 515. 

4 

Schellenberg 1896. 

8 Moreau 1916.


B. CONTENTS AND PRODUCTS OF THE FUNGAL CELLS 

a. CELL-SUBSTANCES. The cells of lichen hyphae contain protoplasm 

and nucleus with glucoses. It is doubtful if starch has been found in fungal 

a carbo- 

hyphae ; it is replaced, in some of the tissues at least, by glycogen, 

hydrate (C 6 H 10 O s ) very close to, if not identical with, animal glycogen, a 

substance which is soluble in water and colours reddish-brown (wine-red) 

with iodine. Errera 1 

first detected its presence in Ascomycetes where it is 

associated with the epiplasm of the cells, more especially of the asci, and he 

considered it to be physiologically homologous with starch. He included 

lichens, as Ascomycetes, in his survey of fungi and quotes, in support of his 

view that lichen hyphae also contain glycogen, a statement made by Schwen- 

dener 2 that "the contents of the ascogenous hyphae of Coenogonium Linkii 

stain a deep-brown with iodine." Errera also instances the red-brown reaction 

with iodine, described by de Bary 3 

, as characteristic of the large spores of 

Ochrolechia (Lecanora}pallescens, while the germinating tubes of these spores 

become yellow with iodine like ordinary protoplasm. Glycogen has been, 

so far, found only in the cells of the reproductive system. 

Iodine was found by Gautier 4 in the gonidia of Parmelia and Peltigera, 

i.e. both in bright-green and blue-green algae. The amount was scarcely 

calculable. 

Herissey 5 claims to have established the presence of emulsin in a large 

series of lichens belonging to such widely separated genera as Cladonia, 

Cetraria, Evernia, Peltigera, Perttisaria, Parmelia, Ramalina, and Usnea. It 

is a ferment which acts upon amygdalin, though its presence has been 

proved in plants such as lichens where no amygdalin has been found*. 

Diastase was demonstrated in the cells of Roccella tinctoria, R. Montagnei 

and oiDendrographa leucophaea by Ronceray 7 who states that, in conjunction 

with air and ammonia, it forms orchil, the well-known colouring substance 

of these lichens. Diastatic ferments have also been determined 8 in Usnea 

florida, Physcia parietina, Parmelia perlata and Peltigera canina. 

b. CALCIUM OXALATE. Oxalic acid (C 2H 2O4) is an oxidation product 

of alcohol and of most carbohydrates and in combination is a frequent 

constituent of plant cells. Knop 9 held that it was formed in lichens by the 

reduction and splitting of lichen acids, though, as Zopf 10 has pointed out, 

these are generally insoluble. Hamlet and Plowright 11 demonstrated the 

presence of free oxalic acid in many families of fungi including Pezizae and 

Sphaeriae. The acid combines with calcium to form the oxalate (CaC 2O 4 ), 

which in the crystalline form is very common in lichens. In the higher 

1 Errera 1882. 


5 

Herissey 1898. 

6 

Czapek 1905, II. p. 257. 

9 

Knop 1872. 

10 

Zopf 1907. 

3 De Bary 1866-1867, p. 211. 

' 

8 

4 Gautier 1899. 

Ronceray 1904. Zopf in Schenk 1890, p. 448. 

u Hamlet and Plowright 1877.

2i 4 

PHYSIOLOGY 

plants the crystals are formed within the cell, but in lichens they are always 

deposited on the outer surface of the hyphal membranes, mainly of the 

medulla and the cortex. 

Calcium oxalate was first detected in lichens by 

1 

Henri Braconnot who 

, 

extracted it by treating the powdered thallus of a number of species (Pertusaria 

communis, Diploschistes scruposus, etc.) with different reagents. The 

in lichens : 2 found that it was abundant 

quantity present varies greatly Zopf 

in all the species inhabiting limestone, and states that in such plants the 

more purely lichenic acids are relatively scarce. Errera 3 has calculated the 

amount of calcium oxalate in Lecanora esculenta, a desert lime-loving 

lichen, to be about 60 per cent, of the whole substance of the thallus. 

Euler 4 

gives for the same lichen even a larger proportion, 66 per cent, of 

the dry weight. In Pertusaria communis, a corticolous species, the oxalate 

occurs as irregular crystalline masses in the medulla (Fig. 116) and has 

been calculated as 47 per 

cent, of the 

whole substance. Other crustaceous species 

such as Diploschistes scrufiosus, Haematomma 

coccineum, H. ventosum, Lecanora 

saxicola, Lecanora tartarea, etc., contain 

large amounts either in the form of octahedral 

crystals or as small granules. 

Rodahl' has recently made obser- 

gonidia; c, medulla; rf, crystal of cal- vations as to the presence of the oxalate 

ciuni oxalate. x ca. 100. ., in / i i_ r> / r\c 

in the thallus of the brown Parmehae. Of 

the fourteen species examined by him, eleven contained calcium oxalate as 

octahedral crystals or as small prisms, often piled up in thick irregular 

masses. Usually the crystals were located in the medullary part of the 

thallus, but in two species, Parmelia verruculifera and P. papulosa, they 

were abundant on the surface cells of the upper cortex. 

c. IMPORTANCE OF CALCIUM OXALATE TO THE LICHEN PLANT. It is 

natural to conclude that a substance of frequent occurrence in any group of 

have not been 

plants is of some biological significance, and suggestions 

lacking as to the value of oxalic acid or of calcium oxalate in the economy 

of the lichen thallus. Oxalic acid is known to be one of the most efficient 

solvents of argillaceous earth and of iron oxides likely to be in the soil. 

These materials are also conveyed to the thallus as air-borne dust, and would 

thus, with the aid of the acid, be easily dissolved and absorbed. As a direct 

proof of this, Knop 6 has stated that lichen-ash always contains argillaceous 

earth. According to Kratzmann 7 

, aluminium, a product of clay, is stored 

up in various lichens. He proved the amount in the ash of Umbilicaria 

1 Braconnot 1825. 


2 

Zopf 1907. 

6 

Knop 1872. 


7 Kratzmann 1913. 

4 Euler 1908, p. 7.


pustulata to be 4/46 per cent., in Usnea barbata 179 pe.r cent., in U. longissima 

considerable quantities while in Roccella tinctoria it occurred in great abun- 

dance. It was also abundant in Diploschistes scruposus, 28' 17 per cent.; it 

declined in Variolaria (Pertusaria) dealbata to 777 per cent., in Cladonia 

rangiferina to 176-2-12 per cent, and in Ramalina fraxinea to r8 per cent. 

Calcium oxalate is directly advantageous to the thallus by virtue of the 

capacity of the crystals to reduce or prevent evaporation, as has been 

pointed out 1 

by Zukal . A like service afforded by crystals to the leaves of 

the higher plants in desert lands has been described by Kerner 2 . These 

are frequently encrusted with lime crystals which allow the copious night 

dews to soak underneath them to the underlying cells, while during the day 

they impede, if they do not altogether check, evaporation. 

Calcium oxalate crystals are insoluble in acetic acid, soluble in hydro- 

chloric acid without evolution of gas; they deposit gypsum crystals in 

a solution of sulphuric acid. 

C. OIL-CELLS 

a. OIL-CELLS OF ENDOLITHIC LICHENS. Calcicolous immersed lichens 

are able to dissolve the lime of the substratum, and their hyphae penetrate 

more or less deeply into the rock. In some forms the entire thallus may 

thus be immersed, the fruits alone being visible on the surface of the stone. 

In two such species, Verrncaria calciseda and Petractis (Gyalecta) exantJie- 

matica, Steiner 3 detected peculiar sphaeroid or barrel-shaped cells that 

differed from the other hyphal cells of the thallus, not only in their form, 

but in their greenish-coloured contents. Similar cells were found by Zukal 4 

in another immersed (endolithic) lichen, Verrucaria f. rupestris rosea. He 

and filled with a 

describes them as roundish organs crowded on the hyphae 

greenish shimmering protoplasm. He 5 found the same types of sphaeroid 

and other swollen cells in the immersed thallus of several calcicolous lichens 

and he finally determined the contents as fat in the form of oil. He found 

also that these fat-cells, though very frequent, were not constantly present 

even in the same species. His observations were confirmed by Hulth 6 for 

a number of allied crustaceous lichens that grow not only on limestone but 

on volcanic rocks. In them he found a like variety of fat-cells intercalary or 

torulose cells, terminal sphaeroid cells and hyphae containing scattered oil- 

drops. Bachmann 7 followed with a study of the thallus of purely calcicolous 

lichens. The specialized oil-cells were fairly constant in the species he 

examined, and, as a rule, they were formed either in the tissues immediately 

below, or at some distance from, the gonidial zone. Funfstuck 8 has also 

1 Zukal 1895, p. 1311. 

5 Zukal 1886. 6 Hulth 1891. 

- Kerner and Oliver 1894, p. 235. 


3 Steiner 1881. 

4 Zukal 1884. 

8 Funfstuck 1895.

216 PHYSIOLOGY 

published an account .of various oil-cells in a large series of calcicolous 

lichens (Fig. 117). 

The occurrence of oil- (or fat-) cells is not dependent on the presence of any 

particular alga as the gonidium of 

Fig. 117. Lecidea immersa Ach. A, sphaeroid 

fat-cells from about 8 mm. below the surface 

x 550. B, oil-hyphae in process of : 

emptying 

a, sphaercid cells containing oil ; b, cells with 

oil-globules x 600 (after Fiinfstiick). 

the lichen. Funfstuck 1 has described 

the immersed thallus of Opegrapha 

saxicola as one of those richest in 

fat-cells. The gonidia belong to the 

a filamentous alga Trentepohlia um- 

brina and form a comparatively 

thin layer about 160/4 thick near 

the upper surface; isolated algal 

branches may grow down to 350/4 

into the rock, while the fungal ele- 

ments descend to 1 1-5 mm., and 

though the very lowest hyphae were 

without oil as were those imme- 

diately beneath the gonidia the 

interlying filaments, he found, were 

crowded with oil-cells. Sphaeroid 

terminal cells were not present. 

Fiinfstiick 1 has re-examined the 

thallus of Petractis exanthematica, 

an almost wholly immersed lichen 

with a gelatinous gonidium, a species 

of Scytonema. The thallus is homoio- 

merous : the alga forms no special 

zone, it intermingles with the hyphae 

dowr n to the very base of the 

thallus; the hyphae are extremely 

slender and at the base they measure 

only about I/A in width. Oil-cells 

are abundant in the form of inter- 

calary cells about 3-5/4 in thickness. Nearer the surface sphaeroid cells 

are formed on short lateral outgrowths ; they measure 14-16/4 in diameter 

and occur in groups of 15 to 20. The superficial part of the thallus is a 

mere film ; the hyphae composing it are slightly stouter and more thickly 

interwoven. 

Bachmann 2 3 and Lang have further described the anatomy of endolithic 

thalli especially with reference to oil-cells, and have supplemented the 

researches of previous workers. New methods of cutting the rock in thin 

1 Fiinfstiick 1899. 

2 Bachmann 1904' . 

3 Lang 1906.


slices and of dissolving away the lime enabled them to see the tissues in 

their relative positions. In these immersed lichens, as described by them and 

by previous writers, and more especially in calcicolous species, the gonidial 

zone of Protococcaceous algae lies near the surface of the rock, and is 

mingled with delicate, thin-walled hyphae which usually do not contain oil. 

The more deeply immersed layer is formed of a weft of equally thin-walled 

hyphae, some of the cells of which are swollen and filled with fat globules. 

These oil-cells may occur at intervals along the hyphae or they may form 

an almost continuous row. In addition, strands or bundles of hyphae (Fig. 

1 1 8) containing few or many oil globules traverse the tissue, and true 

Fig. r 1 8. Biatorella (Sarcogyne) simplex Br. and Rostr. 

a, sphaeroid oil-cells ; b, strand of oil-hyphae from 

10-15 mm. below the surface, x 585 (after Lang). 

sphaeroid cells are generally present. These latter arise in great numbers 

on short lateral branchlets, usually near the tip of a filament and the groups 

of cells are not unlike bunches of grapes. Sometimes the oil-cells are massed 

together into a complex tissue. Hyphae from this layer pierce still deeper 

into the rock and constitute the rhizoidal portion of the thallus. They also 

produce sphaeroid oil-cells in great abundance (Fig. 119). 

Fig. 119. Biatorella pruinosa Mudd. a, complex of sphaeroid 

oil-cells from lomm. below the surface; t>, hypha of sphaeroid 

cells also from inner part of the thallus. x 585 (after Lang). 

In the immersed


thallus of Sarcogyne (Biatorella) pruinosa Lang 1 estimated the gonidial zone 

as 1 75-200 /A in thickness, while the colourless hyphae penetrated 

to a depth of quite 15 mm. 

the rock 

b. OIL-CELLS OF EPILITHIC LICHENS. The general arrangement of the 

tissues and the occurrence and form of the oil-cells vary in the different 

species according to the nature of the substratum. This has been clearly 

demonstrated by Bachmann 2 in Aspicilia (Lecanora} calcarea, an almost 

exclusively calcareous lichen as the name implies. 

On limestone, he found sphaeroid cells formed in 

great abundance on the deeply penetrating rhizoidal 

hyphae (Fig. 120). On a non-calcareous 

brick substratum 3 

, 

a specimen had grown which of 

necessity was epilithic. The cortex and gonidial 

Fig. 120. Lecanora (Aspi- zone together were 40 ft thick; immediately below 

cilia) cah-area Sommerf. 

there were hyphae with irregular cells free from oil ; 

Early stage of sphaeroid 

cell formation x 175 (after lower still there was formed a compact tissue of 

globose fat-cells. In this case the calcareous lichen 

still retained the capacity to form oil-cells on the non-calcareous impene- 

trable substance. 

Very little oil is formed, as a rule, in the cells of siliceous crustaceous 

lichens which are almost wholly epilithic, but Bachmann found a tissue of 

oil-cells in the thallus of Lecanora caesiocinerea, from Labrador, on a granite 

composed of quartz, orthoclase and traces of mica. A thallus of the same 

species collected in the Tyrol, though of a thicker texture, contained no oil. 

Bachmann 3 

suggests no explanation of the variation. 

On granite, rhizoidal hyphae penetrate the rock to a slight extent 

between the different crystals, but only in connection with the mica 4 are 

typical sphaeroid cells formed. 

5 

More or less specialized oil-cells have been demonstrated by Fiinfstiick 

in several superficial (epilithic) lichens which grow on a calcareous substratum, 

as for instance Lecanora (Placodium] decipiens, Lecanora crassa and 

other similar species. The oil in these lichens is usually restricted to more or 

less swollen or globose cells; but it may also be present in the ordinary 

hyphae as globules. Zukal 6 found that the smooth little round granules 

sprinkled over the thallus of the soil-lichens, Baeomyces roseus and B. nifus, 

contained in the hyphae typical sphaeroid oil-cells and that they were 

specially well developed in specimens from Alpine situations. In still another 

soil-lichen, Lecidea granulosa, shimmering green oil was found in short-celled 

torulose hyphae. 

Rosendahl's 7 researches on the brown Parmeliae resulted in the unex- 

1 

2 

Lang 1906, p. 171. Bachmann 3 1 4 

1892. Bachmann . 1904 Bachmann *. 1904 

6 Fiinfstuck 1895. Zukal 1895, p. 1372. ROSendahl 1907.


pected discovery of specialized oil-cells situated in the cortices upper and 

lower of five species out of fourteen which he examined. In one of the 

species, P.papulosa, they also occurred in the cortex of the rhizoids. The 

oil-cells were thinner-walled and larger than the neighbouring cortical cells ; 

they were clavate or ovate in form and sometimes formed irregular external 

processes. They were more or less completely filled with oil which coloured 

brown with osmic acid, left a fat stain on paper and, when extracted, burned 

with a shining reddish flame. These oil-cells were never formed in the 

medulla nor in the gonidial region. 

c. SIGNIFICANCE OF OIL-FORMATION. Zukal 1 

regarded the oil stored 

in these specialized cells as a reserve product of service to the plant in the 

strain of fruit-formation, or in times of prolonged drought or deprivation of 

light. According to his observations fat was most freely formed in lichens 

when periods of luxuriant growth alternated with periods of starvation. He 

cites, as proof of his view, the frequent presence of empty sphaeroid cells, 

and the varying production of oil affected by the condition, habitat, etc. of 

the plant. Fiinfstiick 2 on the other , hand, considers the oil of the sphaeroid 

and swollen cells as an excretion, representing the waste products of metabolism 

in the active tissue, but due chiefly to the presence of an excess of 

carbonic acid which, being set free by the action of the lichen acids on the 

carbonate of lime, forms the basis of fat-formation. He points out that the 

development of fat-cells is always greater in endolithic species in which the 

gonidial layer the assimilating tissue is extremely reduced. In epilithic 

lichens with a wide gonidial zone, the formation of oil is insignificant. He 

states further that if the oil were a direct product of assimilation, the cells 

in which it is stored would be found in contact with the gonidia, and that 

is rarely the case, the maximum of fat production being always at some 

distance. 

Fiinfstuck tested the correctness of his views by a prolonged series of 

growth experiments; he removed the gonidial layer in an endolithic lichen, 

and found that fat storage continued for some time afterwards, its production 

being apparently independent of assimilative activity. The correctness of 

his deductions was further proved by observations on lichens from glacier 

stones. In such unfavourable conditions the gonidia were scanty or absent, 

having died off, but the hyphae persisted and formed oil. He 3 also placed 

in the dark two quick-growing calcicolous lichens, Verrucaria calciseda and 

Opegrapha saxicola. At the end of the experiment, he found that they had 

increased in size without using up the fat. Lang 4 also is inclined to reject 

Zukal's theory, seeing that the fat is formed at a distance from the tissues 

reproductive and others in need of food supply. He agrees with Fiinf- 

stiick that the oil is an excretion and represents a waste-product of the plant. 

1 Zukal 1895. 



4 Lang 1906.


Considerable light is thrown on the subject of oil-formation by the results 

of recent researches on the nutrition of algae and fungi. Beijerinck 1 made 

comparative cultures of diatoms taken from the soil, and he found that so 

long as culture conditions were favourable, any fat that might be formed 

was at once assimilated. If, however, some adverse influence checked the 

growth of the organism while carbonic acid assimilation was in full vigour, 

fat was at once accumulated. The adverse influence in this case was the 

lack of nitrogen, and Beijerinck considers it an almost universal rule in plants 

and animals, that where there is absence of nitrogen, in a culture otherwise 

suitable, fat-oils will be massed in those cells which are capable of forming 

oil. He observed that in two of the cultures of diatoms the one which alone 

was supplied with nitrogen grew normally, while the other, deprived of 

nitrogen, formed quantities of oil-drops. Wehmer 2 recordsthe same experience 

in his cultural study of Aspergillus. Sphaeroid fat-cells, similar to those 

described by Zukal in calcicolous lichens, were formed in the hyphae of a 

culture containing an overplus of calcium carbonate, and he judged, entirely 

on morphological grounds, that these were not of the nature of reserve-storage 

cells. 

Stahel 3 has definitely established the same results in cultures of other 

filamentous fungi. In an artificial culture medium in which nitrogen was 

almost wholly absent, the cells of the mycelium seemed to be entirely 

occupied byoil-drops, and this fatty condition he considered to be a symptom 

of degeneration due to the lack of nitrogen. These experiments enable us 

to understand how the hyphae of calcicolous lichens, buried deep in the 

substratum, deprived of nitrogen and overweighted with carbonic acid, may 

suffer from fatty degeneration as shown by the formation of" sphaeroid-cells." 

The connection between cause and effect is more obscure in the case of 

lichens growing on the surface of the soil, such as Baeomyces roseus, or of 

tree lichens such as the brown Parmeliae, but the same influence lack of 

sufficient nitrogenous food may be at work in those as well as in the endolithic 

species, though to a less marked extent 

It seems probable that the capacity to form oil- or fat-cells has become 

part of the inherited development of certain lichen species and persists 

through changes of habitat as exemplified in Lecanora calcarea*. 

In considering the question of the formation and the function of fat in 

plant cells, it must be remembered that the service rendered to the life of 

the organism by this substance is a very variable one. In the higher plants 

(in seeds, etc.) fat undoubtedly functions in the same way as starch and 

other carbohydrates as a reserve food. It" is evidently not so in lichens, and 

in one of his early researches, Pfeffer 8 

proved that similarly oil was only 

1 

Beijerinck 1904. 

* Wehmer 1891. 

5 Pfeffer 1877. 

3 Stahel 1911. 

* See p. 218.


an excretion in the cells of hepatics. He grew various species in which oilcells 

occurred in the dark and then tested the cell contents. He found that 

after three months of conditions in which the formation of new carbohydrates 

was excluded, the oil in the cells, instead of having served as reserve material, 

was entirely unchanged and must in that instance be regarded as an 

excretion. 

D. LICHEN-ACIDS 

a. HISTORICAL. The most distinctive and most universal of lichen pro- 

ducts are the so-called lichen-acids, peculiar substances found so far only in 

lichens. They occur in the form of crystals or minute granules deposited in 

greater or less abundance as excretory bodies on the outer surface of the 

hyphal cells. Though usually so minute as scarcely to be recognized as 

crystals, yet in a fairly large series their form can be clearly seen with a 

high magnification. Many of them are colourless; others are a bright yellow, 

orange or red, and give the clear pure tone of colour characteristic of some 

of our most familiar lichens. 

The first definite discovery of a lichen-acid was made towards the begin- 

ning of the nineteenth century 

and is due to the researches of C. H. Pfaff1 . 

He was engaged in an examination of Cetraria islandica, the Iceland Moss, 

which in his time was held in high repute, not only as a food but as a tonic. 

He wished to determine the chemical properties of the bitter principle con- 

tained in it, which was so much prized by the Medical Faculty of the period, 

though the bitterness had to be removed to render palatable the nutritious 

substance of the thallus. He succeeded in isolating an acid which he tested 

and compared with other organic acids and found that it was a new substance, 

nearest in chemical properties to succinic acid. In a final note, he states 

that the new :< 

lichen-acid," as he named it, approached still nearer to boletic 

acid, a constituent of a fungus, though it was distinct from that substance 

also in several particulars. The name " cetrarin " was proposed, at a later 

date, by Herberger 2 who described it as a " subalkaloidal substance, slightly 

soluble in cold water to which it gives a bitter taste; soluble in hot water, 

but, on continued boiling, throwing down a brown powder which is slightly 

soluble in alcohol and readily soluble in ether." Knop and Schnederman 3 

found that Herberger's "cetrarin" was a compound substance and contained 

besides other substances " cetraric acid " and lichesterinic acid. It has now 

been determined by Hesse 4 as fumarprotocetraric acid (C

222 

PHYSIOLOGY 

After this first isolation of a definite chemical substance, further research 

was undertaken, and gradually a number of these peculiar acids were recog- 

nized, the lichens examined being chiefly those that were of real or supposed 

economic value either in medicine or in the arts. In late years a wider 

chemical study of lichen products has been vigorously carried on, and the 

results gained have been recently arranged and published in book form by 

Zopf 1 . Many of the statements on the subject included here are taken from 

that work. Zopf gives a description of all the acids that had been discovered 

up to the date of publication, and the methods employed for extracting each 

substance. The structural formulae, the various affinities, derivatives and 

properties of the acids, with their crystalline form, are set forth along with 

a list of the lichens examined and the acids peculiar to each species. In 

many instances outline figures of the crystals obtained by extraction are 

given. For a fuller treatment of the subject, the student is referred to the 

book itself, as only a general account can be attempted here. 

b. OCCURRENCE AND EXAMINATION OF LICHEN-ACIDS. Acids have 

been found, with few exceptions, in all the lichens examined. They are 

sometimes brightly coloured and are then easily visible under the microscope. 

Generally their presence can only be determined by reagents. Over 140 

different kinds have been recognized and their formulae determined, though 

many are still imperfectly known. As a rule related lichen species contain 

the same acids, though in not a few cases one species may contain several 

different kinds. In growing lichens, they form I to 8 per cent, of the dry 

weight, and as they are practically, while unchanged, insoluble in water, they 

are not liable to be washed out by rain, snow or floods. Their production 

seems to depend largely on the presence of oxygen, as they are always 

found in greatest abundance on the more freely aerated parts of the thallus, 

such as the soredial hyphae, the outer rind or the loose medullary filaments. 

They are also often deposited on the exposed disc of the apothecium, on the 

tips of the paraphyses, and on the wall lining the pycnidia. They are absent 

from the thallus of the Collemaceae, these being extremely gelatinous lichens 

in which there can be little contact of the hyphae with the atmosphere. 

No free acids, so far as is known, are contained in Sticta fuliginosa, but 

a compound substance, trimethylamin, is present in the thallus of that lichen. 

It has also been affirmed that acids do not occur in any Peltigera nor in 

two species of Nephromium, but Zopf 1 has extracted a substance peltigerin 

both from species of Peltigera and from the section Peltidea. 

For purposes of careful examination freshly gathered lichens are most 

serviceable, as the acids alter in herbarium or stored specimens. It is well, 

when possible, to use a fairly large bulk of material, as the acids are often 

present in small quantities. The lichens should be dried at a temperature 

* Zopf .907.


not above 40 C. for fear of changing the character of the contained substances, 

and they should then be finely powdered. When only a small 

quantity of material is available, it has been recommended that reagents 

should be applied and the effect watched under the microscope with a low 

power magnification. This method is also of great service in determining 

the exact position of the acids in the thallus. 

In microchemical examination, Senft 1 

deprecates the use of chloroform, 

ether, etc., seeing that their too rapid evaporation leaves either an amorphous 

or crystalline mass of material which does not lend itself to further examina- 

tion. He recommends as more serviceable some oil solution, preferably 

"bone oil" (neat's-foot oil), in which a section of the thallus should be broken 

up under a cover-glass and subjected to a process of slow heating; some 

days must elapse before the extraction is complete. The surplus oil is then 

to be drained off, the section further bruised and the substance examined. 

Acids in bulk should be extracted by ether, acetone, chloroform, 

benzole, petrol-ether and lignoin or by carbon bisulphide. Such solvents as 

alcohols, acetates and alkali solutions should not be used as they tend to 

split up or to alter the constitution of the acids. For the same reason, the 

use of chloroform is to a certain extent undesirable as it contains a percentage 

of alcohol. Ether and acetone, or a mixture of both, are the most efficient 

solvents, and all acids can be extracted by their use, if the material is left 

to soak a sufficient length of time, either in the cold or warmed. It is 

however advisable to follow with a second solvent in case any other acid 

should be present in the tissues. Concentrated sulphuric acid dissolves out 

all acids but often induces colour changes in the process. 

All known lichen-acids form crystals, though the crystalline form may 

alter with the solution used. After filtering and distilling, the residue will 

be found to contain a mixture of these crystals along with other substances, 

which may be removed by washing, etc. 

c. CHARACTER OF ACIDS. Many 

lichen-acids are more or less bitter to 

the taste; they are usually of an acid nature though certain of the substances 

are neutral, such as zeorin, a constituent of various Lecanoraceae.Physciaceae 

and Cladoniaceae, stictaurin, originally obtained from Sticta aurata, lei- 

phemin, from Haematonima coccineum, and others. 

A large proportion are esters or alkyl salts formed by the union of an 

alcohol and an acid; these are insoluble in alkaline carbonates. It is con- 

sidered probable that the fungus generates the acid, while the alcohol arises 

in the metabolic processes in the alga. 

It has indeed been proved that the 

alcohol, erythrit, is formed in at least two algae, Protococcus vulgaris and 

Trentepohlia jolithns ; and the lichen-acid, erythrin (CaoH^do), obtained 

from species of Roccella in which the alga is Trentepohlia, is, according to 

1 Senft 1907.

224 

PHYSIOLOGY 

Hesse, the erythrit ester of lecanoric acid (C 16 H 14 O 7 ), a very frequent constituent 

of lichen thalli. It is certain that the interaction of both symbionts is 

Tobler 1 

necessary for acid production. This was strikingly demonstrated by 

in his cultural study of the lichen thallus. He succeeded in growing, to a 

limited extent, the hyphal part of the thallus of Xanthoria parietina on 

artificial media; but the filaments remained persistently colourless until he 

thereafter the 

added green algal cells to the culture. Almost immediately 

characteristic yellow colour appeared, proving the presence of parietin, 

formerly known as chrysophanic acid. Tobler's observation may easily be 

verified in plants from natural habitats. A depauperate form of Placodittm 

citrinum consisting mainly of a hypothallus of felted hyphae, with minute 

scattered granules containing algae, was tested with potash, and only the 

hyphae immediately covering the algal granules took the thallus gave no reaction. 

stain; the hypo- 

It has been suggested 2 that when a decrease of albumenoids takes place, 

the quantity of lichen-acid increases, so that the excreted substance should 

be regarded as a sort of waste product of the living plant, "rather than as a 

product of deassimilation." The subject is not yet wholly understood. 

d. CAUSES OF VARIATION IN QUANTITY AND QUALITY OF LICHEN- 

ACIDS. Though it has been proved that lichen-acids are formed freely all 

the year round on any soil or in any region, it happens occasionally that 

they are almost or entirely lacking in growing plants. Schwarz 3 found this 

to be the case in certain plants of Lecanora tartarea, and he suggests that 

the gyrophoric acid contained in the outer cortex of that lichen had been 

broken up by the ammonia of the atmosphere into carbonic acid and orcin 

which is soluble in water, and would thus be washed away by rain. It has 

also been shown by Schwendener 4 and others that the outer layers of the 

older thallus in many lichens slowly perish, first breaking up and then peeling 

off; the denuded areas would therefore have lost, for some time at least, 

their particular acids. Fiinfstuck 5 considers that the difference in the presence 

and amount of acid in the same species of lichen may be due very often 

to variation in the chemical character of the substratum, and this view tallies 

with the results noted by Heber Howe 6 in his study of American Ramali- 

nae. He observed that, though all showed a pale-yellow reaction with potash, 

those growing on mineral substrata gave a more pronouncedly yellow colour. 

M. C. Knowles 7 found that in Ramalina scopulontm the colour reaction 

to potash varied extremely, being more rapid and more intense, the more 

the plants were subject to the influence of the sea-spray. 

Lichen-acids are peculiarly abundant in soredia, and as, in some species, 

1 Tobler 1909. 

2 Keegan 1907. 

8 FiinfstUck 1902. 

3 Schwarz 1880, p. 264. 

6 Heber Howe 1913. 


7 Knowles 1913.


the thallus forms these outgrowths, or even becomes leprose more freely in 

damp weather, the amount of acids produced may depend on the amount of 

moisture in the atmosphere. 

Their formation is also strongly influenced by light, as is well shown by 

the varying intensity of colour in some yellow thalli. Placodium elegans, 

always a brightly coloured lichen, changes from yellow to sealing-wax red 

in situations exposed to the full blaze of the sun. Haematomma ventosum, 

though greenish-yellow in lowland situations is intensely yellow in the high 

Alps. The same variation of colour is characteristic of Rhizocarpon geographicum 

which is a bright citron-yellow at high altitudes, and becomes 

more greenish in hue as it nears the plains. The familiar foliose lichen 

Xanthoriaparietina is a brilliant orange-yellow in sunny situations, but grey- 

green in the shade, and then yielding only minute quantities of parietin. 

West 1 and others have noted its more luxuriant growth and brighter colour 

when it grows in positions where nitrogenous food is plentiful, such as the 

roofs of farm-buildings, which are supplied with manure-laden dust, and 

boulders by the sea-shore frequented by birds. 

e. DISTRIBUTION OF ACIDS. Some acids, so far as is known, are only to 

be found in one or at most in very few lichens, as for instance cuspidatic 

acid which is present in Ramalina cuspidata, and scopuloric acid, a constituent 

of Ramalina scopulorum, the acids having been held to distinguish by their 

reactions the one plant from the other. 

Others of these peculiar products are abundant and widely distributed. 

Usninic acid, one of the commonest, has been determined in some 70 species 

belonging to widely diverse genera, and atranorin, a substance first discovered 

in Lecanora atra, has been found again many times; Zopf gives a list of 

about 73 species 

or varieties from which it has been extracted. Another 

widely distributed acid is salazinic acid which has been found by Lettau 2 in 

a very large number of lichens. 

E. CHEMICAL GROUPING OF LICHEN-ACIDS 

Most of these acids have been provisionally arranged by Zopf in groups 

under the two great organic series: I. The Fat series; and II. The Benzole 

or Aromatic series. 

I. LICHEN-ACIDS OF THE FAT SERIES 

Group i. Colourless substances soluble in alkali, the solution not coloured 

by iron chloride. Exs. protolichesterinic acid (C^HÔ^ obtained from species 

of Cetraria, and roccellic acid (C^HÔ^ from species of Roccella, from 

Lecanora tartarea, etc. 

1 West, W. 1905. 

2 I-ettau 1914. 

S. L. I 5


Group 2. Neutral colourless substances insoluble in alkalies, but soluble 

in alcohol, the solution not coloured by iron chloride. Exs. zeorin (C^HÔ^, 

a product of widely diverse lichens, such as Lecanora (Zeord) sulphured, 

Haematomma coccineum, Physcia caesia, Cladonia deformis, etc. and barbatin 

(C 9H 14O), a product of Usnea barbata. 

Group 3. Brightly coloured acids, yellow, orange or red, all derivatives 

of pulvinic acid (Ci8H 12O 5 a ), laboratory compound which has not been found 

in nature. The group includes among others vulpinic acid (C 19 Hi 4O 5) from 

the brilliant yellow Evernia (Letharia) vulpina, stictaurin (CseHÔg) deposited 

in orange-red crystals on the hyphae of Sticta aurata, and rhizocarpic acid 

(CaeHaoOg) chiefly obtained from Rhizocarpon geographicum : it crystallizes 

out in slender citron-yellow prisms. 

Group 4. Only one acid, usninic (Ci 8H ]6O 7 ), a derivative of acetylacetic 

acid, is placed in this group. It is of very wide-spread occurrence, having 

been found in at least 70 species belonging to very different genera and 

families of crustaceous shrubby and leafy lichens. Zopf himself isolated it 

from 48 species. 

Group 5. The thiophaninic acid (d 2H 6O 9 ) group representing only a 

small number. They are all sulphur-yellow in colour and soluble in alcohol, 

the solution becoming blackish-green or dirty blue on the addition of iron 

chloride, with one exception, that of subauriferin obtained from the yellowcoloured 

medulla of Parmelia subaurifera which stains faintly wine-red in 

an iron solution. Thiophaninic acid, which gives its name to this group, 

occurs in Pertusaria lutescens and P. Wulfenii, both of which are yellowish 

crustaceous lichens growing mostly on the trunks of trees. 

II. LICHEN-ACIDS OF THE BENZOLE SERIES 

The larger number of lichen-acids belong to this series, of which 94 at 

least are already known. They are divided into two subseries: I. Orcine 

derivatives, and II. Anthracene derivatives. 

SUBSERIES I. ORCINE DERIVATIVES 

Zopf specially insists that the grouping of this series must be regarded 

as only a provisional arrangement of the many lichen-acids that are included 

therein. All of them are split up into orcine and carbonic acid by ammonia 

and other alkalies. On exposure to air, the ammoniacal or alkaline solution 

changes gradually into orceine, the colouring principle and chief constituent 

of commercial orchil. Orcine is not found free in nature. The orcine sub- 

series includes five groups: 

Group i. The substances in this group form, with hypochlorite of lime 

("CaCl"), red-coloured compounds which yield, on splitting, orsellinic acid. 

Zopf enumerates seven acids as belonging to this group, among which is


lecanoric acid (Ci 6H 14O 7 ), found in many different lichens, e.g. Roccella tinctoria, 

Lecanora tartarea, etc.: whenever there is a differentiated pith and 

cortex it occurs in the pith alone. Erythrin (CaoHÔjo), a constituent of the 

British marine lichen Roccella fuciformi's, also belongs to this orsellinic group. 

Group 2. Substances which also form red products with CaCl, but do 

not break up into orsellinic acid. Among the most noteworthy are olivetoric 

acid (C 21H 26O 7 a constituent of Evernia ), furfuracea, perlatic acid (C^HÔu,) 

and glabratic acid (C^HÔn), which are obtained from species of Parmelia. 

Group 3. Contains three acids of somewhat restricted occurrence. They 

do not form red products with CaCl, and they yield on splitting everninic 

acid. They are: evernic acid (Ci 7H 16O 7 ), found in Evernia prunastri var. 

vulgaris, ramalic acid (C 17H 16O 7) in Ramalina pollinaria, and umbilicaric acid 

(CasHÔn) in species of Gyrophora. 

Group 4. The numerous acids of this group are not easily soluble and 

have a very bitter taste. They are not coloured by CaCl ; when extracted 

with concentrated sulphuric acid, the solution obtained is reddish-yellow or 

deep red. Among the most frequent are fumarprotocetraric acid (C^HÔss), 

the bitter principle of Cetraria islandica, Cladonia rangiferina^ etc., psoromic 

acid (CaoHuOg), obtained from Alectoria implexa, Lecanora varia, Cladonia 

pyxidata and many other lichens, and salazinic acid (Ci 9HuO 10 ), recorded by 

Zopf as occurring in Stereocaulon salazinum and in several Parmeliae, but 

now found by Lettau 1 to be very wide-spread. He used micro-chemical 

methods and detected its presence in 72 species from twelve different families. 

The distribution of the acid in the thallus varies considerably. 

Group 5. This is called the atranorin group from one of the most im- 

portant members. They are colourless substances and, like the preceding 

group, are not affected by CaCl, but when split they form bodies that colour 

a more or less deep red with that reagent. Atranorin (C 19 Hi 8O 8) is one of 

the most widely spread of all lichen-acids; it occurs in Lecanoraceae, Par- 

meliaceae, Physciaceae and Lecideaceae. Barbatinic acid (C 19 HÔ 7 ), another 

member, is found in Usnea ceratina, Alectoria ochroleuca and in a variety of 

Rhizocarpon geographicum. A very large number of acids more or less fully 

studied belong to this group. 

SUBSERIES II. ANTHRACENE DERIVATIVES 

The constituents of this subseries are derived from the carbohydrate 

anthracene, and are characterized by their brilliant colours, yellow, red.brown, 

red-brown or violet-brown. So far, only ten different kinds have been isolated 

and studied. Parietin 2 

(Cj6H 12O 5 ), one of the best known, has been extracted 

{wn\Xanthoriaparietina,Placodium murorum and several other bright-yellow 

1 Lettau 1914. 

8 Parietin differs chemically from chrysophanic acid of Rheum, etc. 

15 

2

228 

PHYSIOLOGY 

lichens; solorinic acid (C 16H 14O 5) occurs in orange-red crystals on the hyphae 

of the pith and under surface of Solorina crocea; nephromin (C 16H 12O 6) is 

found in the yellow medulla of Nephromium lusitanicum ; 

rhodocladonic acid 

(C 12H 8O 6 or C 14H 10O 7) is the red substance in the apothecia of the red-fruited 

Cladoniae. 

There are, in addition, a short series of coloured substances which are of 

uncertain position. They are imperfectly known and are of rare occurrence. 

An acid containing nitrogen has been extracted from Roccella fuciformis, 

and named picroroccellin 1 

(C^HssNgOs). It crystallizes in comparatively large 

prisms, has an exceedingly bitter taste, and is very sparingly soluble. It is 

the only lichen-acid in which nitrogen has been detected. 

One acid at least, belonging to the Fat series, vulpinic acid, which gives the 

greenish-yellow colour to Letharia vulpina, has been prepared synthetically 

by Volkard 2 . 

F. CHEMICAL REAGENTS AS TESTS FOR LICHENS 

The employment of chemical reagents as colour tests in the determination 

of lichen species was recommended by Nylander 3 in a paper published by 

him in 1866. Many acids had already been extracted and examined, and 

as they were proved to be constant in the different species where they 

occurred, he perceived their systematic importance. As an example of the 

new tests, he cited the use of hypochlorite of lime, a solution of which, 

applied directly to the thallus of species of Roccella, produced a bright-red 

"erythrinic" reaction. Caustic potash was also found to be of service in 

demonstrating the presence of parietin in lichens by a beautiful purple 

stain. Many lichenologists eagerly adopted the new method, as a sure and 

ready means of distinguishing doubtful species ; but others have rejected 

the tests as unnecessary and not always to be relied on, seeing that the 

acids are not always produced in sufficient abundance to give the desired 

reaction, and that they tend to alter in time. 

The reagents most commonly in use are caustic potash, generally indicated 

by K ; hypochlorite of calcium or bleaching powder by CaCl and 

; 

a solution of iodine by I. The sign -f signifies a colour reaction, while 

indicates that no change has followed the application of the test solution. 

Double signs ^ or any similar variation indicate the upper or lower parts of 

the thallus affected by the reagent. In some instances the reaction only 

follows after the employment of two reagents represented thus: K (CaCl) +. 

In such a case the potash breaks up the particular acid and compounds are 

formed which become red, orange, etc., on the subsequent application of 

hypochlorite of lime. 

1 Stenhouse and Groves 1877. 

2 Volkard 1894. 

3 Nylander 1866.


As an instance of the value of chemical tests, Zopf cites the reaction of 

hypochlorite of lime on the thallus of four different species of Gyrophora, 

the "tripe de roche": 

Gyrophora torrefacta CaCl + . 

polyrhiza CaCl +. 

proboscidea CaCl . 

erosa CaCl I. 

It must however be borne in mind that these species are well differentiated 

and can be recognized, without difficulty, by their morphological characters. 

Experienced systematists like Weddell refuse to accept the tests unless 

they are supported by true morphological distinctions, as the reactions are 

not sufficiently constant. 

G. CHEMICAL REACTIONS IN NATURE 

Similar colour changes may often be observed in nature. The acids of 

the exposed thallus cortex are not unfrequently split up by the gradual 

action of the ammonia in the atmosphere, one of the compounds thus set 

free being at the same time coloured by the alkali. Thus salazinic acid, a 

constituent of several of our native Parmeliae, is broken up into carbonic 

acid and salazininic acid, the latter taking a red colour. Fumarprotocetraric 

acid is acted on somewhat similarly, and the red colour may be seen in 

Cetraria at the base of the thallus where contact with soil containing 

ammonia has affected the outer cortex of the plant. The same results are 

produced still more effectively when the lichen comes into contact with 

animal excrement. 

Gummy exudations from trees which are more or less ammoniacal may 

also act on the thallus and form red-coloured products on contact with the 

acids present. Lecanora (Aspicilta) cinerea is so easily affected by alkalies 

that a thin section left exposed may become red in time owing to the 

ammonia in the atmosphere. 

II. GENERAL NUTRITION 

A. ABSORPTION OF WATER 

Lichens are capable of enduring almost complete desiccation, but though 

water is 

they can exist with little injury through long periods of drought, 

essential to active metabolism. They possess no special organs for water 

conduction, but absorb moisture over their whole surface. Several inter- 

dependent factors must therefore be taken into account in considering the 

question of absorption : the type of thallus, whether gelatinous or non- 

gelatinous, crustaceous,foliose or fruticose,as also the nature of the substratum 

and the prevailing condition of the atmosphere.

2 3o t PHYSIOLOGY 

a. GELATINOUS LICHENS. The algal constituent of these lichens is 

some member of the Myxophyceae and is provided with thick gelatinous 

walls which have great power of imbibition and swell up enormously in 

damp surroundings, becoming reservoirs of water. Species of Collema, for 

instance, when thoroughly wet, weigh thirty-five times more than when 

dry 1 

. There are no interstices in the thallus and frequently no cortex in 

these lichens, but the gelatinous substance itself forms on drying an outer 

skin that checks evaporation so that water is retained within the thallus 

for a longer period than in non-gelatinous forms. They probably always 

retain some amount of moisture, as they share with gelatinous algae the 

power of revival after long desiccation. 

Gelatinous lichens are entirely dependent on a surface supply of water: 

their hyphae or rhizinae when present rarely penetrate the substratum. 

type 

b. CRUSTACEOUS NON-GELATINOUS LICHENS. The lichens with this 

of thallus are in intimate contact with the substratum whether it be 

on the under surface of the 

soil, rock, tree or dead wood. The hyphae 

thallus function primarily as hold-fasts, but if water be retained in the 

substratum, the lichen will undoubtedly benefit, and water, to some extent, 

will be absorbed by the walls of the hyphae or will be drawn up by capillary 

attraction. In any case, it could only be surface water that would be avail- 

able, as lichens have no means of tapping any deeper sources of supply. 

Lichens are, however, largely independent of the substratum for their 

supply of water. 

2 

Sievers who , gave attention to the subject, found that 

though some few crustaceous lichens took up water from below, most of 

them absorbed the necessary moisture on the surface or at the edges of the 

thallus or areolae, where the tissue is looser and more permeable. The 

swollen gelatinous walls of the hyphae forming the upper layers of such 

lichens are admirably adapted for the reception and storage -of water, 

though, according 

to Zukal 3 

, less hygroscopic generally than in the larger 

forms. Beckmann 4 

proved this power of absorption, possessed by the upper 

cortex, by placing a crustaceous lichen, Haematomma sp., in a damp 

chamber: he found after a while that water had been taken up by the cortex 

and by the gonidial zone, while the lower medullary hyphae had remained dry. 

Herre 5 has recorded an astonishing abundance of lichens from the desert 

of Reno, Nevada, and these are mostly crustaceous forms, belonging to 

a limited number of species. The yearly rainfall of the region is only about 

eight or ten inches, and occurs during the winter months, chiefly as snow. 

It is during that period that active vegetation goes on; but the plants still 

manage to exist during the long arid summer, when their only possible 

water supply is that obtained from the moisture of the atmosphere during 

the night, or from the surface deposit of dews. 

1 

Jumelle 1892. 

2 Sievers 1908. 

3 Zukal 1895. 

4 Beckmann 1907. 

5 Herre 1911-.

GENERAL NUTRITION 231 

c. FOLIOSE LICHENS. Though many of the leafy lichens are provided 

with a tomentum of single hyphae, or with rhizinae on the under surface, 

the principal function of these structures is that of attaching the thallus. 

Sievers 1 tested the areas of absorption by placing pieces of the thallus of 

Parmeliae, of Evernia furfuracea, and of Cetraria glauca in a staining 

solution. After washing and cutting sections, it was seen that the coloured 

fluid had penetrated by the upper surface and by the edge of the thallus, 

as in crustaceous forms, but not through the lower cortex. 

By the same methods of testing, he proved that water penetrates not 

only by capillarity between the closely packed hyphae, but also within the 

cells. A considerable number of lichens were used for experiment, and 

great variations were found to exist in the way in which water was taken 

up. It has been proved that in some species of Gyrophora water is absorbed 

from below: in those in which rhizinae are abundant, water is held by them 

and so gradually drawn up into the thallus; the upper cortex in this genus 

is very thick and checks transpiration. Certain other northern lichens such 

as Cetraria islandica, Cladonia rangiferin'a, etc., imbibe water very slowly, 

and they, as well as Gyrophora, are able to endure prolonged wet periods. 

That foliose lichens do not normally contain much water was proved by 

Jumelle 2 who compared the weight of seven different species when freshly 

he found that the proportion of fresh weight 

gathered, and after being dried ; 

to dry weight showed least variation in Parmelia acetabulum, as ri4 to i ; 

in Xanthoria parietina it was as i'2i to I. 

d. FRUTICOSE LICHENS. There is no water-conducting tissue in the 

elongate thallus of the shrubby or filamentous lichens, as can easily be tested 

by placing the base in water: it will then be seen that the submerged parts 

alone are affected. Many lichens are hygroscopic and become water-logged 

when placed simply in damp surroundings. The thallus of Usnea, for 

instance, can absorb many times its weight of water: a mass of Usnea 

filaments that weighed 

been soaked in 

3'8 grms. when dry increased to 13-3 grms. after 

3 

water for twelve hours. Schrenk who made the 

having 

experiment, records in a second instance an increase in weight from 

3-97 grms. to in 8 grms. The Cladoniae retain large quantities of water in 

their upright hollow podetia. The Australian species, Cladonia retepora, the 

podetium of which is a regular network of holes, competes with the Sphagnum 

moss in its capacity to take up water. 

To conclude : as a rule, heteromerous, non-gelatinous lichens do not 

contain large quantities of water, the weight of fresh plants being generally 

about three times only that of the dry weight. Their ordinary water content 

is indeed smaller than that of most other plants, though it varies at once 

with a change in external conditions. It is noteworthy that a number of 

1 Sievers 1908- 

* Jumelle 1892. 

, 

3 Schrenk 1898.

232 

PHYSIOLOGY 

lichens have their habitat on the sea-shore, constantly subject to spray from 

the waves, but scarcely any can exist within the spray of a waterfall, 

possibly because the latter is never-ceasing. 

B. STORAGE OF WATER 

The gonidial algae Gloeocapsa, Scytonema, Nostoc, etc. among Myxophyceae, 

Palmella and occasionally Trentepohlia among Chlorophyceae, have 

more or less gelatinous walls which act as a natural reservoir of water for 

the lichens with which they are associated. In these lichens the hyphae 

for the most part have thin walls, and the plectenchyma when formed as 

below the apothecium in' Collema granuliferum, or as a cortical layer in 

Leptogium is a thin-walled tissue. In lichens where, on the contrary, 

the alga is non-gelatinous as generally in Chlorophyceae or where the 

gelatinous sheath is not formed as in the altered Nostoc of the Peltigera 

thallus, the fungal hyphae have swollen gelatinous walls both in the pith 

and the cortex, and not only imbibe but store up water. 

Bonnier 1 had his attention directed to this thickening of the cell-walls 

as he followed the development of the lichen thallus. He made cultures 

from the ascospore of Physcia (Xanthoria) parietina and obtained a 

fair amount of hyphal tissue, the cell-walls of which became thickened, 

but more slowly and to a much less extent than when associated with the 

gonidia. 

He noted also that when his cultures were kept in a continuously moist 

atmosphere there was much less thickening, scarcely more than in fungi 

ordinarily; it was only when they were grown under drier conditions with 

necessity for storage, that any considerable swelling of the walls took place. 

Further he found that the thallus of forms cultivated in an abundance of 

moisture could not resist desiccation as could those with the thicker 

membranes. These latter survived drying up and resumed activity when 

moisture was supplied. 

C. SUPPLY OF INORGANIC FOOD 

As in the higher plants, mineral substances can only be taken up when 

they are in a state of solution. Lichens are therefore dependent on the substances 

that are contained in the water of : absorption they must receive their 

inorganic nutriment by the same channels that water is conveyed to them. 

a. FoLIOSE AND FRUTICOSE LICHENS. These larger lichens are provided 

with rhizinae or with hold-fasts, which are only absorptive to a very limited 

extent ; the main source of water supply is from the atmosphere and the 

salts required in the metabolism of the cell must be obtained there also 

1 Bonnier 1889*.


from atmospheric dust dissolved in rain, or from wind -borne particles deposited 

on the surface of the thallus which may be gradually dissolved and 

absorbed by the cortical and growing hyphae. That substances received 

from the atmospheric environment may be all important is shown by the 

exclusive habitat of some marine lichens; the Roccellae, Lichinae, some 

species of Ramalina and others which grow only on rocky shores are almost 

as dependent on sea-water as are the submerged algae. Other lichens, such 

as Hydrothyria venosa and Lecanora lacustris, grow in streams, or on boulders 

that are subject to constant inundation, and they obtain their inorganic food 

mainly, if not entirely, from an aqueous medium. 

Though lichens cannot live in an atmosphere polluted by smoke, they 

thrive on trees and walls by the road-side where they are liable to be almost 

smothered by soil-dust. West 1 has observed that they flourish in valleys 

that are swept by moisture laden winds more especially if near to a high- 

with the dust. The favourite habitats 

way, where animal excreta are mingled 

of Xanthoria parietina are the walls and roofs of farm-buildings where the 

dust must contain a large percentage of nitrogenous material ; or stones by 

the sea-shore that are the haunts of sea-birds. Sandstede 2 found on the 

island of Riigen that while the perpendicular faces of the cliffs were quite 

bare, the tops bore a plentiful crop of Lecanora saxicola, Xanthoria lychnea 

and Candellariella mtellina. He attributed their selection of habitat to the 

presence of the excreta of sea-birds. As already stated the connection of 

foliose and fruticose lichens with the substratum is mainly mechanical but 

occasionally a kind of semiparasitism may arise. 

3 

Friedrich gives 

in a species of Usnea of unusually vigorous development. It grew 

an instance 

on bark 

and the strands of hyphae, branching from the root-base of the lichen, 

had reached down to the living tissue of the tree-trunk and had penetrated 

between the cells by dissolving the middle lamella. It was possible to find 

holes pierced in the cell-walls of the host, but it was difficult to decide if 

the hyphae had attacked living cells or were merely preying on dead material. 

Lindau 4 held very strongly that lichen hyphae were non-parasitic, and merely 

split apart the tissues already dead, and the instance recorded by Friedrich 

is of rare occurrence 5 . 

That the substratum does have some indirect influence on these larger 

lichens has been proved once and again. Uloth 6 

, a chemist as well as a 

botanist, made analyses of plants of Evernia prunastri taken from birch bark 

and from sandstone. Qualitatively the composition of the lichen substances 

was the same, but the quantities varied considerably. Zopf 7 

has, more 

recently, compared the acid content of a form of Evernia furfuracea on rock 

with that of the same species growing on the bark of a tree. In the case of 

1 2 3 4 West 1905. 

Sandstede 1904. 

Friedrich 1906. 

Lindau 1895*. 

" 

6 6 See p. 109. 

Uloth 1861. 

Zopf 1903.

234 

PHYSIOLOGY 

the latter, the thallus produced 4 per cent, of physodic acid and 2'2 per cent, 

of atranorin. In the rock specimen, which, he adds, was a more graceful plant 

than the other, the quantities were 6 per cent, of physodic acid, and 275 per 

cent, of atranorin. In both cases there was a slight formation of furfuracinnic 

acid. He found also that specimens of Evernia prunastri on dead wood 

contained 8*4 per cent, of lichen-acids, while in those from living trees there 

was only 4^4 per cent, or even less. Other conditions, however, might have 

contributed to this result, as Zopf 1 found later that this lichen when very 

sorediate yielded an increased supply of atranoric acid. 

Ohlert 2 who made a , 

study of lichens in relation to their habitat, found 

that though a certain number grew more or less freely on either tree, rock 

or soil, none of them was entirely unaffected. Usnea barbata, Evernia pru- 

nastri and Parmelia physodes were the most indifferent to habitat; normally 

they are corticolous species, but Usnea on soil formed more slender filaments, 

and Evernia on the same substratum showed a tendency to horizontal growth, 

and became attached at various points instead of by the usual single base. 

b. CRUSTACEOUS LICHENS. The crustaceous forms on rocks are in a 

more favourable position for obtaining inorganic salts, the lower medullary 

hyphae being in direct contact with mineral substances and able to act 

directly on them. Many species are largely or even exclusively calcicolous, 

and there must be something in the lime that is especially conducive to 

their growth. The hyphae have been traced into the limestone to a depth 

of 15 mm. s and small depressions are frequently scooped out of the rock by 

the action of the lichen, thus giving a lodgement to the foveolate fruit. 

On rocks mainly composed of silica, the lichen has a much harder sub- 

stance to deal with, and one less easily affected by acids, though even silica 

may be dissolved in time. Uloth 4 concluded from his observations that the 

relation of plants to the substratum was chemical even more than physical, 

so far as crustaceous species were concerned. He found that the surface of 

the area of rock inhabited was distinctly marked : even such a hard substance 

as chalcedony was corroded by a very luxuriant lichen flora, the border of 

growth being quite clearly 

sidered to the carbon dioxide liberated by the plant, though oxalic acid, so 

outlined. The corrosive action is due he con- 

frequent a constituent of lichens, may also share in the corrosion. Egeling 5 

made similar observations in regard to the effect of lichen growth on granite 

rocks; and he further noticed that pieces of glass, over which lichens had 

spread, had become clouded, the dulness of the surface being due to a multitude 

of small cracks eaten out by the hyphae. Buchet 6 also gives an instance 

of glass which had been corroded by the action of lichen hyphae. It formed 

1 

Zopf 1907. 

2 

Ohlert 1871. 

3 See p. 75. 

4 Uloth 1861. 

5 

Egeling 1881. Buchet 1890.


part of an old stained window in a chapel that was obscured by a lichen 

growth which adhered tenaciously. When the window was taken down and 

cleaned, it was found that the surface of the glass was covered with small, 

more or less hemispherical pits which were often confluent. The different 

colours in the picture were unequally attacked, some of the figures or draperies 

being covered with the minute excavations, while other parts were intact. 

It happened also, occasionally, that a colour while slightly corroded in one 

pane would be uninjured in another, but the suggestion is made that there 

might in that case have been a difference in the length of attack by the 

lichen. The selection of colours by the lichens might also be influenced by 

some chemical or physical characters. 

Bachmann 1 found that on granite there is equally a selection of material 

by the hyphae: as a rule they avoid the acid silica constituents; while they 

penetrate and traverse the grains of mica which are dissolved by them 

exactly as are lime granules. 

On another rock consisting mainly of muscovite and quartz he 2 found 

that crystals of garnet embedded in the rock were reduced to a powder by 

the action of the lichen. He concludes that the destroying action of the 

hyphae is accelerated by the presence of carbon dioxide given off by the 

lichen, and dissolved in the surrounding moisture. Lang 3 and Stahlecker 4 

have both come to the conclusion that even the quartz grains are corroded 

by the lichen hyphae. Stahlecker finds that they change the quartz into 

amorphous silicic acid, and thus bring it into the cycle of organic life. Chalk 

and magnesia are extracted from the silicates where no other plant could 

procure them. Lichens are generally rare on pure quartz rocks, chiefly, 

however, for the mechanical reason that the structure is of too close a grain 

to afford a foothold. 

D. SUPPLY OF ORGANIC FOOD 

from which so 

a. FROM THE SUBSTRATUM. The Ascomycetous fungi, 

many of the lichens are descended, are mainly saprophytes, obtaining their 

have in some 

carbohydrates from dead plant material, and lichen hyphae 

instances undoubtedly retained their saprophytic capacity. It has been 

proved that lichen hyphae, which naturally could not exist without the 

algal symbiont, may be artificially cultivated on nutrient media without the 

presence of gonidia, though the chief and often the only source ot carbon 

are associated 

supply is normally through the alga with which the hyphae 

in symbiotic union. 

A large number of crustaceous lichens grow on the bark of trees, and 

their hyphae burrow among the dead cells of the outer bark using up the 



3 Lang 1903. 

4 Stahlecker 1906.

23 6 

PHYSIOLOGY 

material with which they come in contact Others live on dead wood, palings, 

etc. where the supply of disintegrated organic substance is even greater ; or 

they spread over withered mosses and soil rich in humus. 

b. FROM OTHER LICHENS. Bitter 1 has recorded several instances ob- 

served by him of lichens growing over other lichens and using up their 

substance as food material. Some lichens are naturally more vigorous than 

others, and the weaker -or more slow growing succumb when an encounter 

takes place. Pertusaria globulifera is one of these marauding species; its 

habitat is among mosses on the bark of trees, and, being a quick grower, it 

easily overspreads its more sluggish neighbours. It can scarcely be considered 

a parasite, as the thallus of the victim is first killed, probably by the action 

of an enzyme. 

Lecanora subfusca and allied species which have a thin thallus are 

frequently overgrown by this Pertusaria and a dark line generally precedes 

the invading lichen; the hyphae and the gonidia of the Lecanorae are first 

killed and changed to a brown structureless mass which is then split up by 

the advancing hyphae of the Pertusaria into small portions. A little way 

back from the edge of the predatory thallus the dead particles are no longer 

visible, having been dissolved and completely used up. Pertusaria amara 

also may overgrow Lecanorae, though, generally, its onward course is 

checked and deflected towards a lateral direction; if however it is in a young 

and vigorous condition, it attacks the thallus in its path, and ahead of it 

appears the rather broad blackish line marking the fatal effect of the enzyme, 

the rest of the host thallus being unaffected. Neither Pertusaria seems to 

profit much, and does not grow either faster or thicker; the thallus appears 

indeed to be hindered rather than helped by the encounter. Biatora (Lecidea) 

quernea with a looser, more furfuraceous thallus is also killed and dissolved 

by Pertusariae; but if the Biatora is growing near to a withering or dead 

lichen it, also, profits by the food material at hand, grows over it and uses it up. 

Bitter has also observed lichens overgrown by Haematomma sp. the ; growth 

of that lichen is indeed so rapid that few others can withstand its approach. 

Another common rock species, Lecanora sordida (L. glaucoma), has a 

vigorous thallus that easily ousts its neighbours. Rhizocarpon geographicum, 

a slow-growing species, is especially liable to be attacked ; from the thallus 

of L. sordida the hyphae in strands push directly into the other lichen in a 

horizontal direction and split up the tissues, the algae persist unharmed for 

some time, but eventually they succumb and are used up; the apothecia, 

though more resistant than the thallus, are also gradually undermined and 

hoisted up by the new growth, till finally no trace of the original lichen is 

left. Lecanora sordida is however in turn invaded by Lecidea insularis 

(L. intumescens} which is found forming 


small orbicular areas on the


Lecanora thallus. It kills its host in patches and the dead material mostly 

drifts away. On any strands that are left Candellariella vitellina generally 

settles and evidently profits by the dead nutriment. It does not spread to 

the living thallus. Lecanora polytropa also forms colonies on these vacant 

patches, with advantage to its growth. 

Even the larger lichens are attacked by these quick-growing crusts. 

Pertitsaria globulifera spreads over Parmelia perlata and P. physodes, 

gradually dissolving and consuming the different thalline layers; the lower 

cortex of the victim holds out longest and can be seen as an undigested 

black substance within the Pertitsaria thallus for some time. As a rule, 

however, the lichens with large lobes grow over the smaller thalli in a purely 

mechanical fashion. 

c. FROM OTHER VEGETATION. Zukal 1 has given instances of association 

between mosses and lichens in which the latter seemed to play the part of 

parasite. The terricolous species Baeomyces rufus (Sphyridium) and Biatora 

decolorans, as well as forms of Lepraria and Variolarta, he found growing 

over mosses and killing them. Stems and leaves of the moss Plagiothecium 

sylvaticum were grown through and through by the hyphae of a Pertusaria, 

and he observed a leaf of Polytrichum commune pierced by the rhizinae of 

a minute Cladonia squamule. The cells had been invaded and the neigh- 

bouring tissue was brown and dead. 

remains is Lecanora 

Perhaps the most voracious consumer of organic 

tartarea, more especially the northern form frigida. It is the well-known 

cud-bear lichen of West Scotland, and is normally a rock species. It has 

an extremely vigorous thickly crustaceous and quick-growing thallus, and 

spreads over everything that lies in its path decaying mosses, dead leaves, 

other lichens, etc. Kihlman 2 has furnished a graphic description of the way 

it covers up the vegetation on the high altitudes of Russian Lapland. More 

than any other plant it is able to withstand the effect of the cold winds that 

sweep across these inhospitable plains. Other plant groups at certain seasons 

or in certain stages of growth are weakened or killed by the extreme cold 

of the wind, and, immediately, a growth of the more hardy grey crust of 

Lecanora tartarea begins to spread over and take possession of the area 

affected very frequently a bank of mosses, of which the tips have been 

destroyed, is thus covered up. In the same way the moorland Cladoniae, 

C. rangiferina (the reindeer moss) and some allied species, are attacked. 

They have no continuous cortex, the outer covering of the long branching 

are thus sensitive to cold and 

podetia being a loose felt of hyphae; they 

liable to be destroyed by a high wind, and their stems, which are blackened 

as decay advances, become very soon dotted with the whitish-grey crust of 

the more vigorous and resistant Lecanora. 

1 Zukal 1879. 

2 Kihlman 1890.

238 

PHYSIOLOGY 

III. ASSIMILATION AND RESPIRATION 

A. INFLUENCE OF TEMPERATURE 

a. HIGH TEMPERATURE. It has been proved that plants without chloro- 

phyll are less affected by great heat than those that contain chlorophyll. 

Lichens in which both types are present are more capable of enduring high 

temperatures than the higher plants, but with undue heat the alga succumbs 

first. In consequence, respiration, by the fungus alone, can go on after 

assimilation (photosynthesis) and respiration in the alga have ceased. 

Most Phanerogams cease assimilation and respiration after being sub- 

jected for ten minutes to a temperature of 50 C. Jumelle 1 made a series of 

experiments with lichens, chiefly of the larger fruticose or foliaceous types, 

with species ofRamatitia, Physcia and Parmelia, also with Evernia prunastri 

and Cladonia rangiferina. He found that as regards respiration, plants 

which had been kept for three days at 45 C., fifteen hours at 50, then five 

hours at 60, showed an intensity of respiration almost equal to untreated 

specimens, gaseous interchange being manifested by an absorption of oxygen 

and a giving up of carbon dioxide. 

The power of assimilation was more : quickly destroyed as a rule it 

failed after the plants had been subjected successively to a temperature of 

one day at 45 C., then three hours at 50 and half-an-hour at 60. The 

assimilating green alga, being less able to resist extreme heat, as already 

stated, succumbed more quickly than the fungus. Jumelle also gives the 

record of an experiment with a crustaceous lichen, Lecidea (Lecanora) sul- 

phurea, a rock species. It was kept in a chamber heated to 50 for three 

hours and when subsequently placed in the sunlight respiration took place 

but no assimilation. 

Very high temperatures may be endured by lichen plants in quite natural 

conditions, when the rock or stone on which they grow becomes heated by 

the sun. Zopf 2 tested the thalli of crustaceous lichens in a hot June, under 

direct sunlight, and found that the thermometer registered 55C. 

b. Low TEMPERATURE. Lichens support extreme cold even better than 

extreme heat. In both cases it is the power of drying up and entering at 

that enables them 

any season into a condition of lowered or latent vitality 

to do so. In winter during a spell of severe cold they are generally in a 

state of desiccation, though that is not always the case, and resistance to 

cold is not due to their dry condition. The water of imbibition is stored in 

the cell-walls and it has been found that lichens when thus charged with 

moisture are able to resist low temperatures, even down to 40 C. or - 50 

as well as when they are dry. Respiration in that case was proved by 

1 

Jumelle 1892. 

- 

Zopf 1890, p. 489.

ASSIMILATION AND RESPIRATION 239 

Jumelle 1 to continue to 10, but assimilation was still possible at a temperature 

of : 40 

Evernia prunastri exposed to that extreme degree of cold, 

but in the presence of light, decomposed carbon dioxide and gave off 

oxygen. 

B. INFLUENCE OF MOISTURE 

a. ON VITAL FUNCTIONS. Gaseous interchange has been found to vary 

according to the degree of humidity present 1 . In lichens growing in sheltered 

positions, or on soil, there is less complete desiccation, and assimilation and 

respiration may be only enfeebled. Lichens more exposed to the air those 

growing on trees, etc. dry almost completely and gaseous interchange may 

be no longer appreciable. In severe cold any water present would become 

frozen and the same effect of desiccation would be produced. At normal 

temperatures, on the addition of even a small amount of moisture the 

respiratory and assimilative functions at once become active, and to an increasing 

degree as the plant is further supplied with water until a certain 

optimum is reached, after which the vital diminish. 

processes begin somewhat to 

Though able to exist with very" little moisture, lichens do not endure 

desiccation indefinitely, and both assimilation and respiration probably cease 

entirely during very dry seasons. A specimen of Cladonia rangiferina was 

kept dry for three months, and then moistened: respiration followed but it 

was very feeble and assimilation had almost entirely ceased. Somewhat 

similar results were obtained with Ramalina farinacea and Usiiea barbata. 

In normal conditions of moisture, and with normal illumination, assimi- 

lation in lichens predominates over respiration, more carbon dioxide being 

decomposed than is given forth; and Jumelle has argued from that fact, 

that the alga is well able to secure from the atmosphere all the carbon 

required for the nutrition of the whole plant. The intensity of assimilation, 

however, varies enormously in different lichens and is generally more powerful 

in the larger forms than in the crustaceous : the latter have often an extremely 

scanty thallus and they are also more in contact with the substratum rock, 

humus or wood on which they may be partly saprophytic, thus obtaining 

carbohydrates already formed, and demanding less from the alga. 

An interesting comparison might be made with fungi in regard to which 

many records have been taken as to their possible duration in a dry state, 

more especially on the viability of spores, i.e. their persistent capacity of 

germination. A striking instance is reported by Weir 2 of the regeneration of the 

sporophores of Polystictus sanguineus, a common fungus of warm countries. 

The plant was collected in Brazil and sent to Munich. After about two years 

in the mycological collection of the University, the branch on which it grew 

1 

Jumelle 1892. 

2 Weir 1919.

24o PHYSIOLOGY 

was exposed in the open among other branches in a wood while snow still 

lay on the ground. In a short time the fungus revived and before the end 

of spring not only had produced a new hymenium, but enlarged its hymenial 

surface to about one-fourth of its original size and had also formed one 

entirely new, though small, sporophore. 

b. ON GENERAL DEVELOPMENT. Lichens are very strongly influenced 

by abundance or by lack of moisture. The contour of the large majority of 

species is concentric, but they become excentric owing to a more vigorous 

development towards the side of damper exposure, hence the frequent onesided 

increase of monophyllous species such as Umbilicariapustulata. Wainio 1 

observed that species of Cladonia growing in dry places, and exposed to full 

sunlight, showed a tendency not to develop scyphi, the dry conditions 

hindering the full formation of the secondary thallus. As an instance may 

be cited Cl.foliacea, in which the primary thallus is much the most abundantly 

developed, its favourite habitat being the exposed sandy soil of sea-dunes. 

Too great moisture is however harmful: 2 

Nienburg has recorded his 

observations on Sphyridium (Baeomyces rufus): on clay soil the thallus was 

pulverulent, while on stones or other dryer substratum it was granular 

warted or even somewhat squamulose. 

Parmeliaphysodes rarely forms fruits, but when growing in an atmosphere 

8 

constantly charged with moisture , apothecia are more readily developed, 

and the same observation has been made in connection with other usually 

barren lichens. It has been suggested that, in these lichens, the abrupt change 

from moist to dry conditions may have a harmful effect on the developing 

ascogonium. 

The perithecia of Pyrenula nitida are smaller on smooth bark 4 such as 

that of CoryluS) Carpinus, etc., probably because the even surface does not 

retain water. 

IV. ILLUMINATION OF LICHENS 

A. EFFECT OF LIGHT ON THE THALLUS 

As fungi possess no chlorophyll, their vegetative body has little or no 

use for light and often develops in partial or total darkness. In lichens the 

alga requires more or less direct illumination; the lichen fungus, therefore, 

in response to that requirement has come out into the : open it is an adaptation 

to the symbiotic life, though some lichens, such as those immersed 

in the substratum, grow with very little light. Like other plants they are 

sensitive to changes of illumination: some species are shade plants, while 

others are as truly sun plants, and others again are able to adapt themselves 

to varying degrees of light. 

1 Wainio 1897, p. 16. 

2 


3 Metzger 1903. 

* Bitter 1899.

ILLUMINATION OF LICHENS 241 

Wiesner 1 made a series of exact observations on what he has termed 

the " 

light-use " of various plants. He took as his standard of unity for the 

higher plants the amount of light required to darken photographic paper in 

one second. When dealing with lichens he adopted a more arbitrary standard, 

calculating as the unit the average amount of light that lichens would receive 

in entirely unshaded positions. He does not take account of the strength or 

duration of the light, and the conclusions he draws, though interesting and 

instructive, are only comparative. 

a. SUN LICHENS. The illumination of the Tundra lichens is reckoned 

by Wiesner as representing his unit of standard illumination. In the same 

category as these are included many of our most familiar lichens, which 

grow on rocks subject to the direct incidence of the sun's rays, such as, for 

instance, Parmelia conspersa, P. prolixa, etc. Physcia tcnella (Jiispidd) is also 

extremely dependent on light, and was never found by Wiesner under of 

full illumination. Dermatocarpon miniatum, a rock lichen with a peltate 

foliose thallus, is at its best from \ to of illumination, but it grows well in 

situations where the light varies in amount from I to ^? . Psora 

(Lecidea) 

lurida, with dark-coloured crowded squamules, grows on calcareous soil 

among rocks well exposed to the sun and has an illumination from I to ^, 

but with a poorer development at the lower figure. Many crustaceous rock 

lichens are also by preference sun-plants as, for instance, Verrucaria calciseda 

which grows immersed in calcareous rocks but with an illumination of. I 

to \\ in more shady situations, where the light had declined to ^, it was 

found to be less luxuriant and less healthy. 

Sun lichens continue to grow in the shade, but the thallus is then reduced 

and the plant is sterile. Zukal has made a list of those which grow best with 

a light-use of I to T\j, though they are also found not unfrequently in habitats 

where the light cannot be more than -$. Among these light-loving plants 

are the Northern Tundra species of Cladonia, Stereocanlon, Cetraria, Par- 

melia, Umbilicaria, and Gyrophora, as also Xanthoria parietina, Placodium 

elegans, P. murorum, etc., with some crustaceous species such as Lecanora 

atra, Haematomma ventosum, Diploschistes scruposus, many species of Leci- 

deaceae, some Collemaceae and some Pyrenolichens. 

Wiesner's conclusion is that the need of light increases with the lowering 

of the temperature, and that full illumination is of still more importance in 

the life of the plants when they grow in cold regions and are deprived of 

warmth: sun lichens are, therefore, to be looked for in northern or Alpine 

regions rather than in the tropics. 

b, COLOUR-CHANGES DUE TO LIGHT. Lichens growing in full sunlight 

frequently take on a darker hue. Cetraria islandica for instance in an open 

situation is darker than when growing in woods; C. aculeata on bare sand- 


S. L. 16

242 

PHYSIOLOGY 

dunes is a deeper shade of brown than when growing entangled among 

heath plants. Parmelia saxatilis when growing on exposed rocks is fre- 

quently a deep brown colour, while on shaded trees it is normally a light 

bluish-grey. 

An example of colour-change due directly to light influences is given by 

Bitter 1 . He noted that the thallus of Parmelia obscurata on pine trees, and 

therefore subject only to diffuse light, grew to a large size and was of a light 

greyish-green colour marked by lighter-coloured lines, the more exposed 

lobes being always the most deeply tinted. In a less shaded habitat or in full 

sunlight the lichen was distinguished by a much darker colour, and the lobes 

were seamed and marked by blackish lines and spots. Bruce Fink 2 noted a 

similar development of dark lines on the thallus of certain rock lichens 

growing in the desert, more especially on Parmelia conspersa, Acarospora 

xanthophana and Lecanora muralis. He attributes a protective function to 

the dark colour and observes that it seemingly spreads from centres of con- 

tinued exposure, and is thus more abundant in older parts of the thallus. 

He contrasts this colouration with the browning of the tips of the fronds of 

fruticose lichens by which the delicate growing hyphae are protected from 

intense light. 

Gallic 3 finds that protection against too strong illumination is afforded 

both by white and dark colourations, the latter because the pigments catch 

the light rays, the former because it throws them back. The white colour 

is also often due to interspaces filled with air which prevent the penetration 

of the heat rays. 

A deepening of colour due to light effect often visible on exposed rock 

lichens such as Parmelia saxatilis is more pronounced still in Alpine and 

tropical species: the cortex becomes thicker and more opaque through the 

cuticularizing and browning of the hyphal membranes, and the massing of 

crystals on the lighted areas. The gonidial layer becomes, in consequence, 

more reduced, and may disappear altogether. Zukal 4 found instances of 

this in species of Cladonia, Parmelia, Roccella, etc. The thickened cortex 

acts also as a check to transpiration and is characteristic of desert species 

exposed to strong light and a dry atmosphere. 

Bitter 5 remarked the same difference of development in plants of Parmelia 

physodes : he found that the better lighted had a thicker cortex, about 20- 

30 jj, in depth, as compared with 15-22/4 or even only 12/u, in the greener 

shade-plants, and also that there was a greater deposit of acids in the more 

highly illuminated cortices, thus giving rise to the deeper shades of colour. 

Many lichens owe their bright tints to the presence of coloured lichen- 

acids, the production of which is strongly influenced by light and by clear 

air. Xanthoria parietina becomes a brilliant yellow in the sunlight: in the 

1 Bitter 1901, p. 465. 

2 Fink 1909. 

3 

Gallic 1908. 

4 Zukal 1896. 

s Bitter 1901.


shade it assumes a grey-green hue and yields only small quantities of 

parietin. Placodium elegans, normally a brightly coloured yellow lichen, 

becomes, in the strong light of the high Alps, a deep orange-red. Rhizo- 

carpon geographicum is a vivid citrine-yellow on high mountains, but is 

almost green at lesser elevations. 

c. SHADE LICHENS. Many species grow where the light is abundant 

though diffuse. Those on tree-trunks rarely receive direct illumination and 

may be generally included among shade-plants. Wiesner found that corticolous 

forms of Parmelia saxatilis grew best with an illumination between 

and y^ of full 

light, and Pertusaria amara from ^ to ^j both of them could 

thrive from ^ to 3^, but were never observed on trees in direct light. Physcia 

ciliaris, which inhabits the trunks of old trees, is also a plant that prefers 

diffuse light. In warm tropical regions, lichens are mostly shade-plants: 

Wiesner records an instance of a species found on the aerial roots of a tree 

with an illumination of only -^. 

In a study of subterranean plants, Maheu 1 

takes note of the lichens that 

he found growing in limestone caves, in hollows and clefts of the rocks, etc. 

A fair number grew well just within the opening of the caves; but species 

such as Cl. cervicornis, Placodium murorum and Xanthoria parietina ceased 

abruptly where the solar rays failed. Only a few individuals of one or two 

species were found to remain normal in semi-darkness: Opegrapha hapalea 

and Verrucaria muralis were found at the bottom of a cave with the thallus 

only slightly reduced. The nature of the substratum in these cases must 

however also be taken into account, as well as the light influences: lime- 

stone for instance is a more favourable habitat than gypsum the ; latter, being 

more readily soluble, provides a less permanent support. 

Maheu has recorded observations on growth in its relation to light in 

the case of a number of lichens growing in caves. 

Physcia obscura grew in almost total darkness; Placodium murorum 

within the cave had lost nearly all colour; Placodium variabile var. deep 

within the cave, sterile; Opegrapha endoleuca in partial obscurity; Verrucaria 

rupestris f. in total obscurity, the thallus much reduced and sterile; Verrucaria 

rupestris in partial obscurity, the asci empty; Homodium (Collema} 

granuliferum in the inmost recess of the cave, sterile, and the hyphae more 

spongy than in the open. 

Siliceous rocks in darkness were still more barren, but a few odd lichens 

were collected from sandstone in various caves : Cladonia squamosa, Parmelia 

perlata var. ciliata, Diploschistes scruposus, Lecidea grisella, Collema nigrescens 

and Leptogium lacerum. 

d. VARYING SHADE CONDITIONS. It has been frequently observed 

that on the trees of open park lands lichens are more abundant on the side 

1 Maheu 1906. 

16 2

244 

PHYSIOLOGY 

of the trunk that faces the prevailing winds. Wiesner 1 remarks that spores 

and soredia would more naturally be conveyed to that side; but there are 

other factors that would come into play: the tree and the branches frequently 

lean away from the wind, giving more light and also an inclined surface that 

would retain water for a longer period on the windward side 2 . Spores and 

soredia would also develop more readily in those favourable conditions. 

In forests there are other and different conditions: on the outskirts, 

whether northern or southern, the plants requiring more light are to be found 

on the side of the trunk towards the outside; in the depths of the forest, 

light may be reduced from ^^ to ^^, and any lichens present tend to be- 

come mere leprose crusts. Krempelhuber 3 has recorded among his Bavarian 

lichens those species that he found constantly growing in the shade: they 

are in general species of Collemaceae and Caliciaceae, several species of 

Peltigera (P. venosa, P. horizontalis and P. polydactyla) ; 

Solorina saccata ; 

Gyalecta Flotovii, G. cupularis; Pannaria microphylla, P. triptophylla, P. 

brunnea; Icmadophila aeruginosa, etc. 

B. EFFECT ON REPRODUCTIVE ORGANS 

In the higher plants, it is recognized that a certain light-intensity is 

necessary for the production of flowers and fruit. In the lower plants, such 

as lichens, light is also necessary for it is reproduction; a common observation 

that well-lighted individuals are the most abundantly fruited. In the higher 

fungi also, the fruiting body is more or less formed in the light. 

a. POSITION AND ORIENTATION OF FRUITS WITH REGARD TO LIGHT. 

There is an optimum of light for the fruits as well as for the thallus in each 

that can be secured. 

species of lichen : in most cases it is the fullest light 

Zukal 4 finds an exception to that rule in species of Peltigera: when 

exposed to strong sunlight, the lobes, fertile at the tips, curve over so that 

to some extent the back of the is apothecium turned to the light; with 

diffuse light, the horizontal position is retained and the apothecia face up- 

wards. In the closely allied genera Nephroma, Nephromium and Nephromopsis, 

the apothecia are produced on the back of the lobe at the extreme 

tip, but as they approach maturity the fertile lobes turn right back and they 

become exposed to direct illumination. In a well-developed specimen the 

full-grown fruits may thus become so prominent all over the thallus, that 

it is difficult to realize they are on reversed lobes. In one species of Cetraria 

(C. cucullatd) the rarely formed apothecia are adnate to the back of the lobe; 

but in that case the margins of the strap-shaped fronds are incurved and 

connivent, and the back is more exposed than the front. 

In Ramalina the frond frequently turns at a sharp angle at the point of. 


a R. Paulson, ined. 

3 Krempelhuber 1861. 

4 Zukal 1896, p. in.


insertion of the apothecium which is thus well exposed and prominent; but 

Zukal 1 

sees in this formation an adaptation to enable the frond to avoid 

the shade cast by the apothecium which may exceed it in width. In most 

lichens, however, and /especially in shade or semi-shade species, the reproductive 

organs are to be found in the best-lighted positions. 

b. INFLUENCE OF LIGHT ON COLOUR OF FRUITS. Lichen-acids are 

secreted freely in the apothecium from the tips of the paraphyses which give 

the colour to the disc, and as acid-formation is furthered by the sun's rays, 

the well-lighted fruits are always deeper in hue. The most familiar examples 

are the bright-yellow species that are rich in chrysophanic acid (parietin). 

Hedlund 2 has recorded several instances of varying colour in species of 

Micarea (Biatorina, etc.) in which very dark apothecia became paler in the 

shade. He also cites the case of two crustaceous species, Lecidea helvola and 

L. sulphnrella, which have white apothecia in the shade, but are darker in 

colour when strongly lighted. 

V. COLOUR OF LICHENS 

The thalli of many lichens, more especially of those associated with blue- 

green gonidia, are hygroscopic, and it frequently happens that any addition 

of moisture affects the colour by causing the gelatinous cell-walls to swell, 

thus rendering the tissues more transparent and the green colour of the 

gonidia more evident. As a general rule it is the dry state of the plant that 

is referred to in any discussion of colour. 

In the large majority of species the colouring is of a subdued tone soft 

bluish-grey or ash-grey predominating. There are, ho\vever, striking ex- 

ceptions, and brilliant yellow and white thalli frequently form a conspicuous 

feature of vegetation. Black lichens are rare, but occasionally the very dart 

brown of foliaceous species such as Gyrophora or of crustaceous species such 

as Verrncaria maura or Buellia atrata deepens to the more sombre hue. 

A. ORIGIN OF LICHEN-COLOURING 

The colours of lichens may be traced to several different causes. 

a. COLOUR GIVEN BY THE ALGAL CONSTITUENT. As examples may 

be cited most of the gelatinous lichens, Ephebaceae, Collemaceae, etc. which 

owe, as in Collema, their dark olivaceous-green appearance, when somewhat 

moist, to the enclosed dark -green gonidia, and their black colour, when dry, 

to the loss of transparency. When the thallus is of a thin texture as in 

Collema nigrescens, the olivaceous hue may remain constant. Leptogiutn 

Burgessii, another thin plant of the same family, is frequently of a purplish 

1 Zukal 1896. 

2 Hedlund 1892, p. 11.

246 

PHYSIOLOGY 

hue owing to the purple colour of the gonidial Nostoc cells. The dull-grey 

crustaceous thallus of the Pannariaceae becomes more or less blue-green 

when moistened, and the same change has been observed in the Hymeno- 

lichens, Cora, etc. 

In Coenogonium, the alga is some species of Trentepohlia, a filamentous 

genus mostly yellow, which often gives 

its colour to the slender lichen 

filaments, the covering hyphae being very scanty. Other filamentous species, 

such as Usnea barbata, etc., are persistently greenish from the bright-green 

Protococcaceous cells lying near the surface of the thalline strands. Many 

of the furfuraceous lichens are greenish from the same cause, especially when 

moist, as are also the larger lichens, Physcia ciliaris, Stereocaulons, Cladonias 

and others. 

b. COLOUR DUE TO LICHEN-ACIDS. These substances, so characteristic 

of lichens, are excreted from the hyphae, and lie in crystals on the outer 

walls; they are generally most plentiful on exposed tissues such as the 

cortex of the upper surface or the discs of the apothecia. Many of these 

crystals are colourless and are without visible effect, except in sometimes 

in Thamnolia vermicularis 1 

whitening the surface, strikingly exemplified ; 

but others are very brightly coloured. These latter belong to two chemical 

groups and are found in widely separated lichens 2 : 

1 . Derivatives of pul vinic acid which are usually of a bright-yellow colour. 

They are the colouring substance of Letharia vulpina, a northern species, not 

found in our islands, of Cetraria pinastri and C. juniperina* which inhabit 

mountainous or hilly regions. The crustaceous species, Lecidea lucida and 

Rhizocarpon geographicum, owe their colour to rhizocarpic acid. 

The brilliant yellow of the crusts of some species of Caliciaceae is due to 

the presence of the substance calycin, while coniocybic acid gives the greenish 

sulphur-yellow hue to Coniocybe furfuracea. Epanorin colours the hyphae 

and soredia of Lecanora epanora a citrine-yellow and stictaurin is the deepyellow 

substance found in the medulla and under surface of Sticta aurata 

and 5. crocata. 

2. The second series of yellow acids are derivatives of anthracene. They 

include parietin, formerly described as chrysophanic acid, which gives the 

conspicuous colour to Xanthoriae

COLOUR OF LICHENS 247 

In many cases, changes in the normal colouring 1 

are caused by the 

breaking up of the acids on contact with atmospheric or soil ammonia. 

Alkaline salts are thus formed which may be oxidized by the oxygen in 

the air to yellow, red, brown, violet-brown or even to entirely black humus- 

like products which are insoluble in water. These latter substances are 

frequently to be found at the base of shrubby lichens or on the under surface 

of leafy forms that are closely appressed to the substratum. 

c. COLOUR DUE TO AMORPHOUS SUBSTANCES. These are the various 

pigments which are deposited in the cell-walls of the hyphae. The only 

instance, so far as is known, of colours within the cell occurs in Baeomyces 

roseus, in which species the apothecia owe their rose-colour to oil-drops in 

the cells of the paraphyses, and in Lecidea coarctata where the spores are 

rose-coloured when young. In a few instances the colouring matter is 

but Bachmann 2 

excreted (Arthonia gregaria and Diploschistes ocellatus); , 

who has made an extended study of this subject and has examined 120 

widely diversified lichens, in the membranes. 

found that with few exceptions the pigment was 

Bachmann was unable to determine whether the pigments were laid down 

by the protoplasm or were due to changes 

in the cell-wall. The middle 

layer, he found, was generally more deeply coloured than the inner one, 

though that was not universal. In other cases the outer sheath was the 

darkest, especially in cortices one to two cells thick such as those of Parmelia 

and P. revoluta, and in the brown thick-walled spores 

of Physcia stellaris and of Rhizocarpon geographicum. Still another variation 

olivacea, P . fuliginosa 

occurs in Parmelia tristis in which the dark cortical cells show an outer 

colourless membrane over the inner dark wall. 

The coloured pigments are mainly to be found in the superficial tissues, 

but if the thallus is split by areolation, as in crustaceous lichens, the internal 

hyphae may be coloured like those of the outer cortex wherever they are 

exposed. The hyphae of the gonidial layer are persistently colourless, but 

the lower surface and the rhizoids of many foliose lichens are frequently 

very deeply stained, as are the hypothalli of crustaceous species. 

The fruiting bodies in many different families of lichens have dark 

coloured discs owing to the abundance of dark-brown pigment in the paraphyses. 

In these the walls, as determined by Bachmann, are composed 

generally of an inner wall, a second outer wall, and the outermost sheath 

which forms the middle lamella between adjacent cells. In some species 

the second wall is pigmented, in others the middle lamella is the one deeply 

coloured. The hymenium of many apothecia and the hyphae forming the 

amphithecium are often deeply impregnated with colour. The wall hyphae 

1 

Knop 1872. 

2 Bachmann 1890.

248 

PHYSIOLOGY 

of the pycnidia are also coloured in some forms; more frequently the cells 

round the opening pore are more or less brown. 

The presence of these coloured substances enables the cell-wall to resist 

chemical reactions induced by the harmful influences of the atmosphere or 

of the substratum. The darker the cell-wall and the more abundant the 

pigment, the less easily is the plant injured either by acids or alkalies. The 

coloured tips of the paraphyses thus give much needed protection to the 

long lived sporiferous asci, and the dark thalline tissues prevent premature 

rotting and decay. 

d. ENUMERATION OF AMORPHOUS PIGMENTS: 

1. Green. Bachmann found several different green pigments: "Lecidea- 

green," colouring red with nitric acid, is the dark blue-green or olive-green 

(smaragdine) of the paraphyses of many apothecia in the Lecideaceae, and 

may vary to a lighter blue; it appears almost black in thalline cells 1 . 

" 

Aspicilia-green " occurs in the thalline margin and sometimes in the 

epithecium of the fruits of species of Asp i cilia; it becomes a brighter green 

on the application of nitric acid. 

" Bacidia-green," also a rare pigment, 

becomes violet with the same acid; it is found in the epithecium of Bacidia 

muscorum and Bacidia acclinis (Lecideaceae). " 

Thalloidima-green " in the 

apothecia of some species of Biatorina is changed to a dirty-red by nitric 

acid and to violet by potash. Still another termed " 

rhizoid-green " 

gives 

the dark greenish colour to the rhizoids of Physciapulverulenta and P. aipolia 

and to the spores of some species of Physcia and Rhizocarpon. It becomes 

more olive-green with potash. 

2. Blue. A very rare colour in lichens, so far found in only a few species, 

Biatora (Lecidea} atrofusca, Lecidea sanguinaria and Aspicilia flavida f. 

coerulescens. It forms a layer of amorphous granules embedded in the outer 

wall of the paraphyses, becoming more dense towards the epithecium. A 

few granules are also present in the hymenium. 

3. Violet. " Arthonia-violet" as it is called by Bachmann is a constituent 

of the tissues of A rtlwnia gregaria, occurring in minute masses always near 

the cortical cells; it is distinct from the bright cinnabarine granules present 

in every part of the thallus. 

4. Red. Several different kinds of red have been distinguished: " Ur- 

ceolaria-red," visible as an interrupted layer on the upper side of the medulla 

in the thallus of Diploschistes ocellatus, a continental species with a massive, 

crustaceous, whitish thallus that shows a faint rose tinge when wetted. 

" 

Phialopsis-red " is confined to the epithecium of the brightly coloured 

1 A similar reaction with nitric acid is produced on the blue hypothalline hyphae of Placynthium 

nigrum.

COLOUR OF LICHENS 249 

apothecia of Phialopsis rubra. 

" 

Lecanora-red," by which Bachmann designates 

the purplish colour of the hymenium, is an unfailing character of 

Lecanora atra\ the colouring substance is lodged in the middle lamella of 

the paraphysis cells; it occurs also in Rhizocarpon geographicum and in Rk. 

viridiatrum\ it becomes more deeply violet with potash. M. C. Knowles 1 

noted the blue colouring of Rh. geographicum growing in W. Ireland near 

the sea and she ascribed it to an alkaline reaction. Two more rare pigments, 

" 

Sagedia-red " and " Verrucaria-red," are found in species of Verrucariaceae. 

These tinge the calcareous rocks in which the lichens are embedded 

a beautiful rose-pink. They are scarcely represented in our country. 

5. Brown. A frequent colouring substance, but also presenting several 

different kinds of pigment which may be arranged in two groups: 

(1) Substances with some characteristic chemical reaction. These 

are of somewhat rare occurrence: " Bacidia-brown " in the middle lamella 

of the paraphyses of Bacidia fuscorubella stains a clear yellow with acids 

or a violet colour with potash ; 

" 

Sphaeromphale-brown," which occurs 

in the perithecia and in the cortex of Staurothele clopismoides, becomes 

deep olive-green with potash, changing to yellow-brown on the application 

of sulphuric acid ; 

" " 

Segestria-brown in Porina lectissima changes to a 

beautiful violet colour with sulphuric acid, while " Glomellifera-brown," 

which is confined to the outer cortical cells of the upper surface of Parmelia 

glomellifera, becomes blue with nitric and sulphuric acids, but gives no reaction 

with potash. Rosendahl 2 confirmed Bachmann's discovery of this 

colour and further located it in corresponding cells of Parmelia prolixa and 

P. locarensis. 

(2) Substances with little or no chemical reaction. There is only 

one such to be noted: " Parmelia-brown," usually a very dark pigment, which 

is lodged in the outer membranes of the cells. It becomes a clearer colour 

with nitric acid, and if the reagent be sufficiently concentrated, some of the 

pigment is dissolved out. Some tissues, such as the lower cortex of some 

Panneliae, maybe so impregnated and hardened, that nothing short of boiling 

acid has any effect on the cells; membranes less deeply coloured and changed, 

such as the cortex of the Gyrophorae, become disintegrated with such drastic 

treatment. With potash the colour becomes darker, changing from a clear 

brown to olivaceous-brown or -green, or in some cases, as in a more faintly 

coloured epithecium, to a dirty-yellow, but the lighter colour produced there 

is largely due to the swelling up of the underlying tissues to which the potash 

penetrates readily between the paraphyses. 

" Parmelia-brown " is a colouring substance present in the dark epithecium 

and hypothecium of the fruits of many widely diverse lichens, and 

1 Knowles 1915. 

2 Rosendahl 1907.

250 

PHYSIOLOGY 

in the cortical cells and rhizoids of many thalli. In some plants the thallus 

is brown both above and below, in others, as in Parmelia revoluta, etc. only 

the under surface is dark-coloured. 

e. COLOUR DUE TO INFILTRATION. There are several crustaceous lichens 

that are rusty-red, the colour being due to the presence 

of iron. These 

lichens occur on siliceous rocks of gneiss, granite, etc., and more especially 

on rocks rich in iron. Iron as a constituent of lichens was first demonstrated 

by John 1 in Ramalina fraxinea and R. calicaris. Grimbel 2 

colour of rust lichens was due to an iron salt, and Molisch 3 

proved that the 

by microscopic 

examination located minute granules of ferrous oxide as incrustations on 

the hyphae of the upper surface of the thallus. Molisch held that the rhizoids 

or penetrating hyphae dissolved the iron from the rocks by acid secretions. 

Rust lichens however grow on rocks that are frequently under water in which 

the iron is already present. 

Among " rusty " lichens are the British forms, Lecanora lacustris, the 

thallus of which is normally white, though generally more or less tinged 

with iron; 

it inhabits rocks liable to inundation. L. Dicksonii owes its fer- 

ruginous colour to the same influences. Lecidea contigua vax.flavicunda and 

L. confluens f. oxydata are rusty conditions of whitish-grey lichens. 

Nilson 4 found rusty lichens occurring frequently in the Sarak-Gebirge, 

more especially on glacier moraines where they were liable, even when un- 

covered by snow, to be flooded by water from the higher reaches. It is the 

thallus that is affected by the iron, rarely if ever are apothecia altered in 

colour. 

1 

John 1819. 

2 Grimbel 1856. 

3 Molisch 1892. 

4 Nilson 1907.

251

CHAPTER VI 

BIONOMICS 

A. GROWTH AND DURATION 

LICHENS are perennial plants mostly of slow growth and of long continuance ; 

there can therefore only be approximate calculations either as to their rate 

of increase in dimensions or as to their duration in time. A series of somewhat 

disconnected observations have however been made that bear directly 

on the question, and they are of considerable interest. 

Meyer 1 was among the first to be attracted by this aspect of lichen life, 

and after long study he came to the conclusion that growth varied in 

rapidity according to the prevailing conditions of the atmosphere and 

the nature of the substratum ; but that nearly all species were very slow 

growers. He enumerates several, Lichen (X anthoria) parietinus, L. (Par- 

melia) tiliaceus.L. (Rhizocarpori)geographicus, L.(Haematommd) ventosus,aind 

L. (Lecanoro) saxicolus, all species with a well-defined outline, which, after 

having attained some considerable size, remained practically unchanged for 

six and a half years, though, in some small specimens of foliose lichens, he 

noted, during the same period, an increase of one-fourth to one-third of their 

size in diameter. In one of the above crustaceous species, .. ventosus,the specimen 

had not perceptibly enlarged in sixteen years, though during that time 

the centre of the thallus had been broken up by weathering and had again 

been regenerated. 

Meyer also records the results of culture experiments made in the open; 

possibly with soredia or with thalline scraps: he obtained a growth of 

Xanthoria parietina (on wrought iron kept well moistened), which fruited in 

the second year, and in five years had attained a width of 5-6 lines (about 

i cm.) ; Lecanora saxicola growing on a moist rock facing south grew 4-7 lines 

in six and a half years, and bore very minute apothecia. 

Lindsay 2 

quotes a statement that a specimen of Lobaria pulmonaria had 

been observed to occupy the same area of a tree after the lapse of half a 

century. Berkeley 3 records that a plant of Rhizocarpon geographicum remained 

in much the same condition of development during a period of twenty-five 

years. The latter is a slow grower and, in ordinary circumstances, it does 

not fruit till about fifteen years after the thallus has begun to form. 

4 Weddell , 

also commenting on the long continuance of lichens, says there are crustaceous 

species occupying on the rock a space that might be covered by a five-franc 

piece, that have taken a century to attain that size. 

Phillips 5 on the other hand argues against the very great age of lichens, 

1 

Meyer 1825, p. 44. 

2 

Lindsay 1856. 

3 

Berkeley 1857. 

* Weddell 1869. 

5 Phillips 1878.

GROWTH AND DURATION 253 

and suggests 20 years as a sufficient time for small plants to establish them- 

selves on hard rocks and attain full development. He had observed a small 

vigorous plant of Xanthoria parietina that in the course of five years had 

extended outwards to double its original size. The centre then began to 

break up and the whole plant finally disappeared. 

Exact measurements of growth have been made by several observers. 

Scott Elliot 1 found that a Pertusaria had increased about half a millimetre 

from the ist February to the end of 2 

September. Vallot kept under observation 

at first three then five different plants of Parmelia saxatilis during a 

period of eight years : the yearly increase of the thallus was half a centimetre, 

so that specimens of twenty centimetres in breadth must have been growing 

from forty to fifty years. 

Bitter's 3 observations on Parmelia physodes agree in the main with those 

of Vallot: the increase of the upper lobes during the year was 3-4 mm. In 

a more favourable climate Heere found that Parmelia caperata (Fig. 49) on 

a trunk ofAescu/us in California had grown longitudinally 1*5 cm. and trans- 

versely i cm. The measurements extended over a period of seven winter 

months, five of them being wet and therefore the most favourable season of 

growth. In warm regions lichens attain a much greater size than in tem- 

perate or northern countries, and growth must be more rapid. 

A series of measurements was also made by Heere 4 on Ramalina reti- 

culata (Fig. 64), a rapid growing tree-lichen, and one of the largest American 

species. The shorter lobes were selected for observation, and were tested 

during a period of seven months from September to May, five of the months 

being in 

' 

the wet season. There was great variation between the different 

lobes but the average increase during that period was 41 per cent. 

Krabbe 5 took notes of the colonization of Cladonia rangiferina (Fig. 127) 

on burnt soil : in ten years the podetia had reached a height of 3 to 5 cm., 

giving an annual growth of about 3-5 mm. It is not unusual to find specimens 

in northern latitudes 18 inches long (50 cm.), which, on that computation, 

must have been 100 to 160 years old; but while increase goes on at the 

apex of the podetia, there is constant perishing at the base of at least as 

much as half the added length and these plants would therefore be 200 or 

300 years old. Reinke 6 indeed has declared that apical growth in these 

Cladina species may go on for centuries, given the necessary conditions of 

good light and undisturbed habitat. 

Other data as to rate of growth are furnished by Bonnier 7 in the account 

of his synthetic cultures which developed apothecia only after two to three 

years. The culture experiments of Darbishire 8 and Tobler 9 with Cladonia 

soredia are also instructive, the former with synthetic spore- and alga-cultures 

1 Scott Elliot 1907. 

6 Reinke 1894, p. 18. 

* 

Vallot 1896. 

3 

Bitter 1901. 

* Heere 1904. 

7 

Bonnier, see p. 29. 

8 

Darbishire, see p. 148. 

s Krabbe 1891, p. 131. 

9 Tobler, see p. 148.

254 

BIONOMICS 

having obtained a growth of soredia in about seven months; the latter, 

starting with soredia, had a growth of well-formed squamules in nine months. 

It has been frequently observed that abundance of moisture facilitates 

growth, and this is nowhere better exemplified than in crustaceous soillichens. 

Meyer found that on lime-clay soil which had been thrown up from 

a ditch in autumn, lichens such as Gyalecta geoica were fully developed the 

following summer. He gives an account also of another soil species, Verrucaria 

(Thrombium) epigaea, which attained maturity during the winter half 

of the year. Stahl 1 

tells us that Thelidium minutulum, a pyrenocarpous soil- 

lichen, with a primitive and scanty thallus, was cultivated by him from spore 

to spore in the space of three months. Such lichens retain more of the 

characteristics of fungi than do those with a better developed thallus. Rapid 

colonization by a soil-lichen was also observed in Epping Forest by Paulson 2 . 

In autumn an extensive growth of Lecidea uliginosa covered as if with a dark 

stain patches of soil that had been worn bare during the previous spring. 

The lichen had reached full development and was well fruited. 

These facts are quite in harmony with other observations on growth 

made on Epping Forest lichens. The writers 3 of the report record the finding 

of " 

fruiting lichens overspreading decaying leaves which can scarcely have 

lain on the ground more than two or three years; others growing on old 

boots or on dung and fruiting freely; others overspreading growing mosses." 

They also cite a definite instance of a mass of concrete laid down in 1903 

round a surface-water drain which in 1910 seven years later was covered 

with Lecanora galactina in abundant fruit; and of another case of a Portland 

stone garden -ornament, new in 1904, and, in 1910, covered with patches of 

a fruiting Verrucaria (probably V. nigrescens}. Both these species, they add, 

have a scanty thallus and generally fruit very freely. 

A series of observations referring to growth and "ecesis" or the spreading 

of lichens have been made by Bruce Fink 4 over a period of eight years. His 

aim was mainly to determine the time required for a lichen to re-establish 

itself on areas from which it had been previously removed. Thus a quadrat 

of limestone was scraped bare of moss and of Leptogium lacerum, except 

for bits of the moss and particles of the lichen which adhered to the 

rock, especially in depressions of the surface. After four years, the moss 

was colonizing many small areas on which grew patches of the lichen 2 to 

10 mm. across. Very little change occurred during the next four years. 

Numerous results are also recorded as to the rate of growth, the average 

being i cm. per year or somewhat under. The greatest rate seems to have 

been recorded for a plant of Peltigera canina growing on " a mossy rock 

along a brook in a low moist wood, well-shaded." A plant, measuring 10 

by 14 cm., was deprived of several large apothecia. The lobes all pointed 

1 Stahl 1877, p. 34. 

2 Paulson 1918. 

3 Paulson and Thompson 1913. 

4 Fink 1917.

GROWTH AND DURATION 255 

in the same direction, and the plant increased 175 cm. in one year. Two 

other plants, deprived of their lobes, regenerated and increased from 2 and 

5 cm. respectively to 3^5 and 6 cm. No other measurements are quite so 

high as these, though a plant of Parmelia caperata (sterile), measuring from 

I to 2 cm. across, reached in eight years a dimension of 10 by 13 cm. Other 

plants of the same species gave much slower rates of increase. A section of 

railing was marked bearing minute scattered squamules of Cladonia pityrea. 

After two years the squamules had attained normal size and podetia were 

formed 2 to 4 mm. long. 

Several areas of Verrucaria muralis were marked and after ten months 

were again measured; the largest plants, measuring 2*12 by 2^4 cm. across, 

had somewhat altered in dimensions and gave the measurements 2'2 by 

3 cm. Some crustose species became established and produced thalli and 

apothecia in two to eight years. Foliose lichens increased in diameter from 

'3 to 3'5 cm - Per year - So far as external appearance goes, apothecia are 

produced in one to eight years; it is concluded that they require four to 

eight years to attain maturity in their natural habitats. 

B. SEASON OF FRUIT FORMATION 

The presence of apothecia (or perithecia) in lichens does not always 

imply the presence of spores. In many instances they are barren, the spores 

having been scattered or not yet matured the disc in these cases is ; 

composed 

of paraphyses only, with possible traces of asci. 

however, some lichens may be found in fruit. 

In any month of the year, 

Baur 1 

found, for instance, that Parmelia acetabulum developed carpogonia 

the whole year round, though somewhat more abundantly in spring and 

autumn. Pertusaria communis similarly has a maximum period of fruit- 

formation at these two seasons. This is probably true of tree-lichens 

generally: in summer the shade of the foliage would inhibit the formation 

of fruits, as would the extreme cold of winter ; but were these conditions 

relaxed spore-bearing fruits might be expected at any season though perhaps 

not continuously on the same specimen. 

An exception has been noted by Baur in Pyrenula nitida, a crustaceous 

tree Pyrenolichen. He found carpogonia only in February and April, and 

the perithecia matured in a few weeks, presumably at a date before the trees 

were in full leaf; but even specimens of Pyrenula are not unusual in full 

spore-bearing conditions in the autumn of the year. 

To arrive at any true knowledge as to the date and duration of spore 

production, it would be necessary to keep under observation a series of one 

species, examining them microscopically at intervals of a few weeks or months 

1 Baur 1901.

256 

BIONOMICS 

and noting any conditions that might affect favourably or unfavourably the 

reproductive organs. A comparison between corticolous and saxicolous 

species would also be of great interest to determine the influence of the 

substratum as well as of light and shade. But in any case it is profitable to 

collect and examine lichens at all seasons of the year, as even when the 

bulk of the spores is shed, there may remain belated apothecia 

asci still intact. 

C. DISPERSAL AND INCREASE 

with a few 

The natural increase of lichen plants may primarily be sought for in the 

dispersal of the spores produced in the fruiting-bodies. These are ejected, 

as in fungi, by the pressure of the paraphyses on the mature ascus. The 

spores are then carried away by wind, water, insects, etc. In a few lichens 

gonidia are enclosed in the hymen ium and are ejected along with the spores, 

but, in most, the necessary encounter with the alga is as fortuitous, and 

generally as certain, as the pollination of anemophilous flowers. A case of 

dispersal in Sagedia microspora has been described by Miyoshi 1 in which 

entire fruits, small round perithecia, were dislodged and carried away 

by the wind. The addition of water caused them to swell enormously and 

brought about the ejection of the spores. Areas covered by the thallus 

are also being continually enlarged by the spreading growth of the hypo- 

thallus. 

a. DISPERSAL OF CRUSTACEOUS LICHENS. These lichens are distributed 

fairly equally on trees or wood (corticolous) and on rocks (saxicolous). Some 

species inhabit both substrata. As regards corticolous lichens that live on 

smooth bark such as hazel or mountain-ash, the vegetative body or thallus 

is generally embedded beneath the epidermis of the host. Soredia are absent 

and the thallus is protected from dispersal. In these lichens there is rather 

an abundant and constant formation of apothecia or perithecia. 

Other species that affect rugged bark and are more superficial are less 

dependent on spore production. The thallus is either loosely granular, or is 

broken up into areolae. The areolae are each a centre of growth, and with 

an accession of moisture they swell up and exert pressure on each other. 

Parts of the thallus thus become loosened and are dislodged and carried 

away. If anchored on a suitable substratum they grow again to a complete 

lichen plant. Sorediate lichens are dependent almost wholly on these bud- 

like portions for increase in number ; soredia are easily separated from 

the parent plant, and easily scattered. Darbishire 2 noted frequently that 

small Poduridae in moving over the surface of Pertusaria amara became 

powdered with soredia and very evidently took a considerable part in the 

dissemination of the species. 

1 

Miyoshi 1901. 

2 Darbishire 1897, p. 657.

DISPERSAL AND INCREASE 257 

Crustaceous rock lichens are rarely sorediate, but they secure vegetative 

propagation l 

by the dispersal of small portions of the thallus. The thalli most 

securely attached are cracked into small areolae which, by unequal growth, 

become very soon lop-sided, or, by intercalary increase, form little warts and 

excrescences on their surface. These irregularities of development give rise 

to more or less tension which induces a loosening of the thallus from the 

substratum. Weather changes act similarly and gradually the areolae are 

broken off. Loosening influence is also exercised by the developing fruits, 

the expanding growth of which pushes aside the neighbouring tissues. Wind 

or water then carries away the thalline particles which become new centres 

of growth if a suitable substratum is reached. 

b. DISPERSAL OF FOLIOSE LICHENS. It is a matter of common observation 

that, in foliose lichens where fruits are abundant, there are few or no 

soredia and vice versa. In either case propagation is ensured. In addition 

to these obvious methods of increase many lichens form isidia, outgrowths 

from the thallus which are easily detached. Bitter 2 considers for instance 

that the coralloid branchlets, which occur in compact tufts on the thallus of 

Uinbilicaria pustulata, are of immense service as organs of propagation. 

Apothecia and pycnidia are rarely present in that species, and the plant 

thus falls back on vegetative production. Slender crisp thalline outgrowths, 

easily separable, occur also on the edges of lobes, as in species of Peltigera, 

Platysvia, etc. 

Owing to the gelatinous character of lichen hyphae, the thallus quickly 

becomes soft with moisture and is then easily torn and distributed by wind, 

animals, etc. The action of lichens on rocks has been shown to be of a 

constantly disintegrating character, and the destruction of the supporting 

rock finally entails the scattering of the plant. This cause of dispersal is 

common to both crustaceous and foliose species. The older central parts of 

a lichen may thus have disappeared while the areolae on lobes of the circumference 

are still intact and in full vigour. 

As in crustaceous lichens the increase in the area of growth may take 

place by means of the lichen mycelium which, originating from the rhizinae 

in contact with the substratum, spreads as a hypothallus under the shelter 

of the lobes and far beyond them. When algae are encountered a new lobe 

begins to form. The process can be seen perhaps most favourably in 

lichens on decaying wood which harbours moisture and thus enables the 

wandering hyphae 

to retain life. 

c. DISPERSAL OF FRUTICOSE LICHENS. Many 

of these lichens are 

abundantly fruited; in others soralia are as constantly developed. Species 

of Usnea, Alectoria, Ramalina and many Cladoniae are mainly propagated 

S. L. 

1 Beckmann 1907. 

'* 

Bitter 1899. 

I 7

258 

BIONOMICS 

by soredia. They are all peculiarly liable to be broken and portions of the 

thallus scattered by the combined action of wind and rain. 

Peirce 1 found that Ramalina reticulata (Fig. 65), of which the fronds are 

an open network, was mainly distributed by the tearing of the lichen in high 

wind. This takes place during the winter rains, when not only the lichen is 

wet and soft in texture, but when the deciduous trees are bare of leaves, at 

a season, therefore, when the drifting thalline scraps can again catch on to 

branch or stem. A series of observations on the dispersal of forms of long 

pendulous Usneas was made by Schrenk 2 . In the Middle and North Atlantic 

States of America these filamentous species rarely bear apothecia. The 

high winds break and disperse them when they are in a wet condition. They 

generally grow on Spruces and Firs, because the drifting filaments are more 

easily caught and entangled on short needles. The successive wetting and 

drying causes them to coil and uncoil, resulting in a tangle impossible to 

unravel, which holds them securely anchored to the support. 

D. ERRATIC LICHENS 

In certain lichens, there is a tendency for the thallus to develop excrescences 

of nodular form which easily become free and drift about in the wind 

while still living and growing. They are carried sometimes very long distances, 

and fall in thick deposits over localities far from their place of origin. The 

most famous instance is the " manna lichen," Lecanora esculenta, which has 

been scientifically examined and described by Elenkin 3 . He distinguishes 

seven different forms of the species: f. esculenta, f. affznis, f. alpina, and 

f. fnttiadosa-foliacea which are Alpine lichens, the remainder, f. desertoides, 

f. foliacea and f. esculenta-tarquina, grow on the steppes or in the desert 4 . 

Elenkin 3 adds to the list of erratic lichens a variety of Parmelia mollius- 

cula along with P. ryssolea from S. Russia, from the Asiatic steppes and 

from Alpine regions. 

5 

Mereschkovsky has also recorded from the Crimea 

Parmelia vagans, probably derived from P. f. conspersa vaga (f. nov.). It 

drifts about in small rather flattened bits, and, like other erratics, it never 

fruits. 

Meyer 6 

long ago described the development of wandering lichens : scraps 

that were torn from the parent thallus continued to grow if there were 

sufficient moisture, but at the same time undergoing considerable change in 

appearance. The dark colour of the under surface disappears in the frequently 

altered position, as the lobes grow out into narrow intermingling fronds 

iorming a more or less compact spherical mass ; the rhizoids also become 

modified and, if near the edge, grow out into threadlike structures which 

Peirce 2 

1898. 

Schrenk 1898. 

5 

Mereschkovsky 1918. 

3 4 

Elenkin 1901. 

See Chap. X. 

6 

Meyer 1825, p. 44.

ERRATIC LICHENS 259 

bind the mass together. Meyer says that " wanderers " have been noted as 

belonging to Pannelid acetabuluin, Platysma glaucum and Anaptychiaciliaris. 

The most notable instance in Britain of the " erratic " habit is that of 

Parmelia revoluta var. concentrica (Fig. 121), first found on Melbury Hill 

Fig. 

li" 

121. Parmelia revoluta var. concentrica Cromb. a, plant on flint with detached fragment; 

b, upper surface of three specimens ; c, three specimens as found on chalk downs ; d, speci 

in section showing central cavity (S. H., Photo.}. 

17 

2

26o BIONOMICS 

near Shaftesbury, Dorset, and described as " a spherical unattached lichen 

which rolls on the exposed downs." It has recently been observed on the 

downs near Seaford in Sussex, where, however, it seems to be confined to a 

small area about eight acres in extent which is exposed to south-west winds. 

The lichen is freely distributed over this locality. To R. Paulson and Somer- 

ville Hastings 1 we owe an account of the occurrence and origin of the revo- 

luta wanderers. The specimens vary considerably in shape and size, and 

measure from I to 7 cm. in longest diameter. Very few are truly spherical, 

some are more or less flattened and many are quite irregular. The revolute 

edges of the overlapping lobes give a rough exterior to the balls, which 

thereby become entangled amongst the grass, etc., and movement is impeded 

or prevented, except in very high winds. Crombie 2 had suggested that the 

concentric plant originated from a corticolous habitat, but no trees are near 

the Seaford locality. Eventually specimens were found growing on flints in 

the immediate neighbourhood. While still on the stone the lichen tends 

to become panniform, a felt of intermingling imbricate lobes is formed, 

portions of which, in time, become crowded out and dislodged. When 

scattered over the ground, these are liable to be trampled on by sheep or 

other animals and so are broken up; each separate piece then forms the 

nucleus of new concentric growth. 

Crombie 2 observed at Braemar, drifting about on the detritus of Morrone, 

an analogous structure in Parmelia omphalodes. He concluded that nodular 

excrescences of the thallus had become detached from the rocks on which 

the lichen grew; while still attached to the substratum Parmelia omphalodes 

and the allied species, P. saxatilis, form dense cushion-like masses. 

E. PARASITISM 

a. GENERAL STATEMENT. The parasitism of Strigula complanata, an 

exotic lichen found on the leaves of evergreen trees, has been already 

described 3 

; Dufrenoy 4 records an instance of hyphae from a Parmelia thallus 

piercing pine-needles through the stomata and causing considerable injury. 

Lichen hyphae have attacked and destroyed the protonemata of mosses. 

Cases have also been recorded of Usnea and Ramalina penetrating to the living 

tissue of the tree on which they grew, and there may be other similar para- 

sitisms ; but these exceptions serve to emphasize the independent symbiotic 

growth of lichens. 

There are however some lichens belonging to widely diverse genera that 

have retained, or reverted to, the saprophytic or parasitic habit of their fungal 

ancestors, though the cases that occur are generally of lichens preying on 

1 Paulson and Somerville Hastings 1914. 

* 

Dufrenoy 1918. 


8 See p. 35.

PARASITISM 261 

other lichens. The conditions have been described as those of " 

antagonistic 

symbiosis " when one lichen is hurtful or fatal in its action on the other, and 

as " parasymbiosis " when the association does little or no injury to the host. 

The parasitism of fungi on lichens, though falling under a different category, 

in many instances exhibits features akin to parasymbiosis. 

The parasitism of fungus on fungus is not unusual; there are instances 

of its occurrence in all the different classes. In the Phycomycetes there are 

genera wholly parasitic on other fungi such as Woronina and other Chytridiaceae 

; Piptocephahts, one of the Mucorini, is another instance. Cicinnobolus, 

one of the Sphaeropsideae, preys on Perisporiae ; 

a species of Cordyceps is 

found on Elaphomyces, and Orbilia coccinella on Polyporus\ while among 

Basidiomycetes, Nyctalis, an agaric, grows always on Russula. 

There are few instances of lichens rinding a foothold on fungi, for the 

simple reason that the latter are too short lived. On the perennial Polyporeae 

a few have been recorded by Arnold 1 but these are not described as , 

doing 

damage to the host. They are mostly species of Lecidea or of allied genera. 

Kupfer 2 has also listed some 15 different lichens that he found on Lenzites sp. 

b. ANTAGONISTIC SYMBIOSIS. In discussing the nutrition of lichens 3 

note has been taken of the extent to which some species by means of enzymes 

destroy the thallus of other lichens in their vicinity and then prey on the 

dead tissues. A constantly cited 4 

example is that of Lecanora atriseda which 

in its early stages lives on the thallus of Rhizocarpon geographicum inhabiting 

mountain rocks. A detailed examination of the relationship between these 

two plants was made by Malme and later by Bitter 5 . Both writers found 

that the Lecanora thallus as it advanced caused a blackening of the Rhizo- 

carpon areolae, the tissues of which were killed by the burrowing slender 

filaments of the Lecanora, easily recognized by their longer cells. The invader 

thereafter gradually formed its own medulla, gonidial layer and cortex right 

over the surface of the destroyed thallus. Lecidea insularis (L. intumescens) 

similarly takes possession of and destroys the thallus of Lecanora glaucoma 

and Malme 4 

strongly suspects that Bnellia verruculosa and B. aethalea may 

be living on the thallus of Rhizocarpon distinctum with which they are 

constantly associated. 

Other cases of facultative parasitism have been studied 

6 

by Hofmann , 

more especially three different species, Lecanora dispersa, Lecanora sp. and 

Parmelia hyperopta, which were found growing on the thick foliose thailus 

of Dermatocarpon miniatum. These grew, at first independently, on a wall 

along with many examples of Endocarpon on to which they spread as opportunity 

offered. The thallus of the latter was in all cases distorted, the area 

occupied by the invaders being finally killed. The attacking lichens had 

1 Arnold 1874. 

- 


Kupfer 1894. 

3 See p. 236. 

6 Hofmann 1906. 

* Malme 1895.

262 BIONOMICS 

benefited materially by the more nutritive substratum : their apothecia were 

more abundant and their thallus more luxuriant. The gonidia especially 

had profited; they were larger, more brightly coloured, and they increased 

more freely. Hoffmann offers the explanation that the strain on the algae of 

providing organic food for the hyphal symbiont was relaxed for the time, 

hence their more vigorous appearance. 

Arthonia subvarians is always parasitic on the apothecia of Lecanora 

galactina, and Almquist 1 discovered that the hymenium of the host alone is 

injured, the hypothecium and excipulum being left intact. 

The " parasitism " of Pertusaria globulifera on Parmelia perlata and 

P.physodes, as described by 

Bitter 2 

, may also be included under antagonistic 

symbiosis. The hyphae pierce the Parmdia thallus, break it up and gradually 

absorb it. Chemical as well as mechanical influences are concerned in the 

work of destruction as both the fungus and the alga of the victim are dissolved. 

Lecanora tartarea already dealt with as a marauding lichen 3 over decaying 

vegetation may spread also to living lichens. Fruticose soil species, such as 

Cetraria aculeata and others, die from the base and the Lecanora gains 

entrance to their tissues at the decaying end which is open. 

Arnold 4 

speaks of these facultative parasites that have merely changed 

their substratum as pseudo-parasites, and he gives a list of instances of such 

change. In many cases it is rather the older thalli that are taken possession 

of, and, in nearly every case, the invader is some crustaceous species. The 

plants attacked are generally ground lichens or more particularly those that 

inhabit damp localities, such as Peltigera or Cladonia or certain bark lichens. 

Drifting soredia or particles of a lichen would easily take hold of the host 

thallus and develop .in suitable conditions. To give a few of the instances 

observed, there have been found, by Arnold, Crombie and others: 

on Peltigera canina: Callopisma cerina, Rinodina turfacea var., Bilimbia 

obscurata and Lecanora aurella; 

on Peltigera aphthosa: Lecidea decolorans; 

on Cladoniae: Bilimbia microcarpa, Bacidia Beckhausii and Urceolaria 

scruposa, etc. 

Urceolaria (Diploschistes) has a somewhat bulky crustaceous thallus which 

may be almost evanescent in its semi-parasitic condition, the only gonidia 

retained being in the margin of the apothecia. Nylander 5 found isolated 

apothecia growing vigorously on Cladonia squamules. 

Hue 6 describes Lecanora aspidophora f. errabunda, an Antarctic lichen, as 

not only a wanderer but as a "shameless robber." It is to be seen everywhere 

on and about other lichens, settling small glomeruli of apothecia here and 

1 

Almquist 1880. 



3 See p. 237. 

6 Hue 1915. 

4 Arnold 1874.


there on the thallus of Umbilicariae or between the areolae of Buelliac, and 

always too vigorous to be ousted from its position. 

Bacidia flavovirescens has been regarded by some lichenologists 1 

as a 

parasite on Baeomyces, but recent work by Tobler 2 seems to have proved 

that the bright green thallus is that of the Bacidia. 

c. PARASYMBIOSIS. There are certain lichens that are obligative parasites 

and pass their whole existence on an alien thallus. They may possibly have 

degenerated from the condition of facultative parasitism as the universal 

history of parasitism is one of increased dependence on the host, and of 

growing atrophy of the parasite, but, in the case of lichens, there is always 

the peculiar symbiotic condition to be considered : the parasite produces its 

own vigorous hyphae and normal healthy fruits, it often claims only a share 

of the carbohydrates manufactured by the gonidia. The host lichen is not 

destroyed by this parasymbiosis though the tissues are very often excited 

to abnormal growth by the presence of the invading organism. 

Lauder Lindsay 3 was one of the first to study these "microlichens" as 

he called them, and he published descriptions of those he had himself 

observed on various hosts. He failed however to discriminate between lichens 

and parasitic fungi. It is only by careful research in each case that the 

affinity to fungi or to lichens can be determined; very frequently the whole 

of them, as possessing no visible thallus, have been classified with fungi, but 

that view ignores the symbiosis that exists between the hyphae of the 

parasite and the gonidia of the host. 

Parasitic lichens are rather rare on gelatinous thalli ; but even among 

these, a few instances have been recorded. Winter 4 has described a species 

of LeptorapJtis, the perithecia of which are immersed in the thallus of Physma 

franconicum. The host is wholly unaffected by the presence of the parasite 

except for a swelling where it is situated. The foreign hyphae are easily 

distinguishable; they wander through the thallus of the host with their free 

ends in the mucilage of the gonidial groups from which they evidently 

extract nourishment. Species of the lichen genus Obryznm are also parasitic 

on gelatinous lichens. 

The parasitic genus Abrothallus* has been the subject of frequent stud}-. 

There are a number of species which occur as little black discs on various 

thalli of the large foliose lichens. They were first of all described as parasitic 

fungi, later Tulasne 6 affirmed their lichenoid nature as proved by the struc- 

ture, consistence and long duration of the apothecia. Lindsay 7 wrote a 

monograph of the genus dealing chiefly with Abrothallus Smithii (Buellia 

Parmeliarunt) and A. oxysporus, with their varieties and forms that occur on 

1 Th. Fries 1874, p. 343. 

"- Tobler 191 1 2 . 

5 Abrothallus has been included in the lichen genus Buellia. 

7 

Lindsay 1856. 

3 Lindsay i86 9 2 . 

4 Winter 1877. 

6 Tulasne 1852.

264 

BIONOMICS 

several different hosts. In some instances the thallus is apparently quite 

unaffected by the presence of Abrothallus, in others, as in Cetraria glauca, 

there is considerable hypertrophy produced, the portion of the thallus on 

which the parasites are situated showing abnormal growth in the form of 

swellings or pustules which may be regarded as gall-formations. Crombie 1 

points this out in a note on C. glauca var. ampullacea, figured first by 

Dillenius, which is merely a swollen condition due to the presence of 

Abrothallus. 

The internal structure and behaviour of Abrothallus has more recently 

been followed in detail by Kotte 2 . He recognized a number of different 

species growing on various thalli of Parmelia and Cetraria, but Abrothallus 

Cetrariae was the only one that produced gall-formation. The mycelium of 

the parasite in this instance penetrates to the medulla of the host lichen as 

a loose weft of hyphae which are divided into more or less elongate cells. 

These send out side branches, which grow towards the algal cells, and by 

their short-celled filaments clasp them exactly in the same way as do the 

normal lichen hyphae. Thus in the neighbourhood of the parasite an algal 

cell may be surrounded by the hyphae not only of the host, but also by 

those of Abrothallus. The two different hyphae can generally be distinguished 

by their reaction to iodine: in some cases Abrothallus hyphae take 

the stain, in others the host hyphae. In addition to apothecia, spermogonia 

or pycnidia are produced, but in one of the species examined by Kotte, 

Abrothallus Peyritschii on Cetraria caperata, there was no spermogonial 

wall formed. The hyphae also penetrate the host soredia or isidia, so that 

on the dispersal of these vegetative bodies the perpetuation of both organisms 

is secured in the new growth. 

Abrothallus draws its organic food from the gonidia in the same way as 

the host species, and possibly the parasitic hyphae obtain also water and 

inorganic food along with the host hyphae. They have been traced down 

to the rhizinae and may even reach the hypothallus, but no injury to the 

host has been detected. It is a case of joint symbiosis and not of parasitism. 

Microscopic research has therefore justified the inclusion of these and other 

forms among lichens. 

d. PARASYMBIOSIS' OF FUNGI. There occur on lichens, certain parasites 

classed as fungi which at an early stage are more or less parasymbionts of 

the host ; 

as growth advances they may become parasitic and cause serious 

damage, killing the tissues on which they have settled. 

Zopf 3 found several instances of such parasymbiosis in his study of 

fungal parasites, such as Rhymbocarpus punctiformis, a minute Discomycete 

which inhabits the thallus of Rhizocarpon geographicum. By means of 

staining reagents he was able to trace the course of the parasitic hyphae, 


2 Kotte 1910. 

3 

Zopf 1896.


and found that they travelled towards the gonidia and clasped them lichen- 

wise without damaging them, since these remained green and capable of 

division. At no stage was any harm caused to the host by the alien 

organism. Another instance he observed was that of Conida rubescens on 

the thallus of Rhizocarpon epipolium. By means of fine sections through the 

apothecia of Conida and the thallus of the host, he proved the presence of 

numerous gonidia in the subhymenial tissue, these being closely surrounded 

by the hyphae of the parasite, and entirely undamaged : 

they retained their 

at first described 

green colour, and in size and form were unchanged. 

1 

Zopf 

these parasites as fungi though later 1 he allows that they may represent 

lower forms of lichens. 

Tobler 2 has added two more of these parasymbiotic species on the border 

line between lichens and fungi, similar to those described by Zopf. One of 

these, Phacopsis vulpina, belonging to the fungus family Celidiaceae, is 

parasitic on Letharia vulpina. The fronds of the host plant are considerably 

altered in form by its presence, being more branched and curly. Where 

the parasite settles a swelling arises filled with its hyphae, and the host 

gonidia almost disappear from the immediate neighbourhood, only a few 

"nests" being found and these very mucilaginous. These nests as well as 

single gonidia are surrounded by Phacopsis hyphae which have gradually 

displaced those of the Letharia thallus. The gonidia are excited to division 

and increase in number on contact with either lichen or fungus hyphae, but 

in the latter case the increase is more abundant owing doubtless to a more 

powerful chemical irritant in the fungus. As development advances, the 

Phacopsis hyphae multiply to the exclusion of both lichen hyphae and 

gonidia from the area of invasion. Finally the host cortex is split, the 

fungus bursts through, and the tissue beneath the parasite becomes brown 

and dead. Phacopsis begins as a "parasymbiont," then becomes parasitic, 

and is at last saprophytic on the dead cells. The hyphae travel down into 

the medulla of the host and also into the soredial outgrowths, and are 

dispersed along with the host. The effect of Verrucula on the host thallus 

may also be cited 3 . 

Tobler gives the results of his examination of still another fungus, Kar- 

schia destructans. It becomes established on the thallus of Chaenotheca 

cJnysoceptiala and its hyphae gradually penetrate down to the underlying 

bark (larch). The lichen thallus beneath the fungus is killed, but gonidia in 

the vicinity are sometimes clasped : Karschia also is thus a parasymbiont, 

then a parasite, and finally a saprophyte. 

Elenkin 4 describes certain fungi which to some extent are parasymbionts. 

One of these, Conidclla urceolata n.sp., grew on forms of Lecanora esculenta. 

The other, a stroma-forming species, had invaded the thallus of Parmelia 

1 

Zopf 1898, p. 249. 

2 Tobler 191 1 2 . 

3 See p. 276. 

4 Elenkin 1901-.

266 BIONOMICS 

molliuscula, where it caused gall-formation. As the growth of the gall was 

due to the co-operation of the lichen gonidia, the fungus must at first have 

been a parasymbiont. Only dead gonidia were present in the stroma; probably 

they had been digested by the parasite. Because of the stroma Elenkin 

placed the fungus in a new genus, Trematosphaeriopsis. 

e. FUNGI PARASITIC ON LICHENS. A solution or extract of lichen 

thallus is a very advantageous medium in which to grow fungi. It is there- 

fore not surprising that lichens are a favourite habitat for parasitic fungi. 

Stahl 1 has noted that the lichens themselves flourish best where there is 

frequent moistening by rain or dew with equally frequent drying which 

effectively prevents the growth of fungi. Species of Peltigera are however 

have been 

able to live in damp conditions : without being injured, they 

observed to maintain their vigour when cultivated in a very moist hothouse 

while all the other forms experimented with were attacked and finally 

destroyed by various fungi. 

Lindsay 2 devoted a great deal of attention to the microscopic study of 

the minute fruiting bodies so frequently present on lichen thalli and published 

descriptions of microlichens, microfungi and spermogonia. He and others 

naturally considered these parasitic organisms to be in many cases either 

the spermogonia or pycnidia of the lichen itself. It is often not easy to 

determine their relationship or their exact systematic position ; many of 

them are still doubtful forms. 

There exists however a very large number of fully recognized parasitic 

microfungi belonging to various genera. Lindsay discovered many of them. 

Zopf 3 has given exact descriptions of a series of forms, with special reference 

to their effect on the host thallus. In an early paper he described a species, 

Pleospora collematum, that he found on Physma compactum and other Collemaceae. 

The hyphae of the parasite differed from those of the host in being 

of a yellow colour; they did not penetrate or spread far, being restricted to 

rhizoid-like filaments at the base of their fruiting bodies (perithecia and 

pycnidia). Their presence caused a slight protuberance but otherwise did 

no harm to the host ; the Nostoc cells in their immediate vicinity were even 

more brightly coloured than in other parts of the thallus. 

4 

In another paper 

he gives an instance of gall-formation in Collema pulposum induced by the 

presence of the fungus Didymosphaeria pulposi. Small protuberances were 

formed on the margins of the apothecia, more rarely on the lobes of the 

thallus, each one the seat of a perithecium of the fungus. No damage was 

done to either constituent of the thallus. 

Agyrium flavescens grows parasitically on the under surface of Peltigera 

polydactyla. M. and Mme Moreau 5 found that the hyphae of the fungus 

spread between the medullary filaments of the lichen; no haustoria were 

1 Stahl 1904. 

2 Lindsay 1859, 1869, 1871. 

3 

Zopf 1896. 

4 

Zopf 1898. 

6 Moreau I9i6 3 .


observed. The mature fruiting body had no distinct excipulum, but was 

surrounded by*a layer of dead lichen cells. 

It is not easy to determine the difference between parasites that are of 

fungal nature and those that are lichenoid ; but as a general rule the fungi 

may be recognized by their more transient character, very frequently by 

their effect on the host thallus, which is more harmful than that produced 

by lichens, and generally by their affinity to fungi rather than to lichens. 

Opinions differ and will continue to differ on this very difficult question. 

The number of such fungi determined and classified has gradually 

increased, and now extends to a very long list. Even as far back as 1896 

Zopf reckoned up 800 instances of parasitism of 400 species of fungi on 

about 350 different lichens and many more have been added. Abbe Vouaux 1 

is the latest writer on the subject, but his work is mostly a compilation of 

species already known. He finds representatives of these parasites in nine 

families of Pyrenomycetes and six of Discomycetes. He leaves out of account 

the much debated Coniocarps, but he includes with fungi all those that have 

been proved to be parasymbiotic, such as Abrotliallus. 

A number of fungus genera, such as Conida, etc., are parasitic only on 

lichens. Most of them have one host only; others, such as Tichothecium 

pygmaeum, live on a number of different thalli. Crustaceous species are often 

selected by the parasites, and no great damage, if any, is caused to these 

hosts, except when the fungus is seated on the disc of the apothecium, so 

that the spore-bearing capacity is lessened or destroyed. 

In some of the larger lichens, however, harmful effects are more visible. 

In Lobaria pulmonaria, the fruits of which are attacked by the Discomycete, 

Celidium Stictarum-, there is at first induced an increased and unusual formation 

of lichen apothecia. These apothecia are normally seated for the most 

part on the margins of the lobes or pustules, but when they are invaded by 

the fungus, they appear also in the hollows between the pustules and even 

on the under surface of the thallus. In the large majority of cases the 

fungus is partly or entirely embedded in the thallus; the gonidia in the 

vicinity may remain green and healthy, or all the tissues in the immediate 

neighbourhood of the parasite may be killed. 

/. MYCETOZOA PARASITIC ON LICHENS. Mycetozoa live mostly on 

decayed wood, leaves, humus, etc. One minute species, L isterella paradoxa, 

always inhabits the podetia of Cladonia rangiferina. Another species, 

Hymenobolina parasitica, was first detected and described by Zukal 3 as a 

true parasite on the thallus of Physciaceae; it has since been recorded in the 

British Islands on Parmeliae*. This peculiar organism differs from other 

mycetozoa in that the spores on germination produce amoebae. These unite 

to form a rose-red plasmodium which slowly burrows into the lichen thallus 

1 Vouaux 1912, etc. 


3 Zukal 1893. 

4 Lister 1911.

268 BIONOMICS 

and feeds on the living hyphae. It is a minute species, but when abundant 

the plasmodia can just be detected with the naked eye as rosy specks 

scattered over the surface of the lichen. Later the grey sporangia are 

produced on the same areas. 

F. DISEASES OF LICHENS 

a. CAUSED BY PARASITISM. Zopf l has stated that of all plants, lichens 

are the most subject to disease, reckoning as diseases all the instances of 

parasitism by fungi or by other lichens. There are however only rare 

instances in which total destruction or indeed any permanent harm to the 

host is the result of such parasitism. At worst the trouble is localized and 

does not affect the organism as a whole. Some of these cases have been 

already noted under antagonistic symbiosis or parasymbiosis. Several 

instances have however been recorded where real injury has been caused 

by the penetration of some undetermined fungus mycelium. Zukal 2 records 

two such observed by him in Parmelia encansta and Physcia villosa : the 

thallus of the former was dwarfed and deformed by the presence of the alien 

mycelium, the latter was excited to abnormal proliferation. 

b. CAUSED BY CROWDING. Lichens suffer frequently from being over- 

grown by other lichens ; they may also be crowded out by other plants. 

My attention was called by Mr P. Thompson to a burnt plot of ground in 

Epping Forest, which, after the fire, had been colonized by Peltigera spuria. 

In the course of a few years, other vegetation had followed, depriving the 

lichen of space and light and gradually driving it out. When last examined 

only a few miserable specimens remained, and these were reduced in vitality 

by an attack of the lichen parasite Illosporium carneum. 

c. CAUSED BY ADVERSE CONDITIONS. Zukal considers as pathological, 

at least in origin, the cracking of the thallus so frequent in crustaceous 

lichens as well as in the more highly developed forms. As the cracks are 

beneficial in the aeration of the plant, they can hardly be regarded as 

symptoms of a diseased condition. The more evident ringed breaks in the 

cortex of Usneae, due probably to wind action, have more reason to be so 

regarded ; they are most pronounced in Usnea articulata, where the portions 

bounded by the rings are contracted and swollen, and a hollow space is 

formed between the cortex and the central axis. The swellings that are 

produced n lichen thalli, such as those of Umbilicaria and some species of 

Gyrophora, due to intercalary growth are normal to the plant, though occasion- 

ally the swollen weaker portions may become ruptured and the cortex be 

thrown off. As pathological also must be regarded the loss of cortex some- 

times occasioned by excessive soredial formation at the margins of the lobes: 

1 Zopf 1897. 

2 Zukal X g96) p< 258 .

DISEASES OF LICHENS 269 

the upper cortex may be rolled back and eventually torn away; the gonidial 

layer is exposed and transformed into soredia which are swept away by the 

wind and rain, till finally only traces of the lower cortex are left. 

Zukal 1 has instanced, as a case of diseased condition observed by him, 

the undue thickening of the cortex in Pertusaria communis whereby the 

formation of the fruiting bodies is inhibited and even vegetative development 

is rendered impossible. There arrives finally a stage when splitting takes 

place and the whole thallus breaks down and disappears. As a rule however 

there need be no limit to the age of the lichen plant. There is no vital 

point or area in the thallus ; injury of one part leaves the rest unhurt, and 

any fragment in growing condition, if it combines both symbionts, can carry 

on the life of the plant, the constant renewal of gonidia preventing either 

decay or death. Barring accidents many lichens might exist as world endures. 

long as the 

G. HARMFUL EFFECT OF LICHENS 

One lichen only, Strigula complanata, a tropical species, has been proved 

to be truly and constantly parasitic. It grows'on the surface of thick leathery 

leaves such as those of Camellia-, etc. and the alga and fungus both penetrate 

the epidermis and burrow beneath the cuticle and outer cells, causing them 

to become brown. It undoubtedly injures the leaves. 

Friedrich 3 has given an isolated instance of the hold-fast hyphae of Usnea 

piercing through the cortex to the living tissue of the host, and not only 

destroying the middle lamella by absorption, but entering the cells. The 

Usnea plant was characterized by exceptionally vigorous growth. Practically 

all corticolous lichens are epiphytic and the injury they cause is of an acci- 

dental nature Crustaceous species on the outer bark occupy the dead 

cortical layers and seem to be entirely harmless 4 . The larger foliose and 

fruticose forms are not so innocuous: by their abundant enveloping growth 

they hinder the entrance of air and moisture, and thus impede the life of 

the higher plant. Gleditsch 5 

, one of the earliest writers on Forestry, first 

indicated the possibly harmful effect of lichens especially on young trees 

and " in addition," he says, " they serve as cover for large numbers of small 

6 

insects which are hurtful in many ways to the trees." Lindau pointed out 

the damage done to pine-needles by Xantkoria parietina which grew round 

them like a cuff and probably choked the stomata, the leaves so clothed being 

of a Parmelia 

mostly withered. Dufrenoy 7 states that he found the hyphae 

entering a pine-needle by the stomata, and that the starch disappeared from 

the neighbouring parenchyma the cells of which tended to disintegrate. 

It is no uncommon sight to see neglected fruit trees with their branches 

crowded with various lichens, Evernia prunaslri, Ramalina farinacea, etc. 

Such lichens often find the lenticels a convenient opening for their hold-fasts 

1 Zukal 1896, p. 255. 

' 

2 

Cunningham 1879. 

3 F"edrich 1906, p. 401. 

* See p. 78. 

5 

Gleditsch 1775, p. 31. 

6 Lindau 1895, p. 53. 

7 

Dufrenoy 1881.

2 7o 

BIONOMICS 

and excercise a smothering effect on the trees. Lilian 

1 Porter distinctly 

states that Ramalinae by their penetrating bases damage the tissues of the 

trees. The presence of lichens is however generally due to unhealthy con- 

ditions already at work. 

2 

Friedrich reported of a forest which he examined, 

in which the atmospheric moisture was very high, with the soil water 

scarce, that those trees that were best supplied with soil water were free 

from lichens, while those with little water at the base bore dead branches 

which gave foothold to a rich growth of the epiphytes. 

Experiments to free fruit trees from their coating of lichens were made 

With a whitewash brush he painted over the infested branches 

by Waite 3 . 

with solutions of Bordeaux mixture of varying strength, and found that this 

solution, commonly in use as a fungicide, was entirely successful. The trees 

were washed down about the middle of March, and some three weeks later 

the lichens were all dead, the fruticose and foliose forms had changed in 

colour to a yellowish or brownish tint and wer.e drooping and shrivelled. 

to the 

Waite was of opinion that the lichens did considerable damage 

trees, but it has been held by others that in very cold climates they may 

provide protection against severe frost. Instances of damage are however 

asserted by Bouly de Lesdain 4 . The 

bark of willows he found was a favourite 

habitat of numerous lichens: certain species, such as Xanthoria parietina, 

completely surrounded the branches, closing the stomata; others, such as 

Physcia ascendens, by the mechanical strain of the rhizoids, first wet and then 

dry, gradually loosened the outer bark and gave entry to fungi which completed 

the work of destruction. 

H. GALL-FORMATION 

Several instances of gall-formation to a limited extent have been already 

noted as caused by parasitic fungi or lichens. Greater abnormality of development 

is induced in a few species by the presence of minute animals, mites, 

wood-lice, etc. Zopf 5 noted these deformations of the thallus in specimens 

of Ramalina Kullensis collected on the coasts of Sweden. The fronds were 

frequently swollen in a sausage-like manner, and branching was hindered or 

altogether prevented; apothecia were rarely formed, though pycnidia were 

abundant. Here and there, on the swollen portions of the thallus, small 

holes could be detected and other larger openings of elliptical outline, about 

\-\\ mm. in diameter, the margins of which had a nibbled appearance. 

Three types of small articulated animals were found within the openings: 

species of mites, spiders and wood-lice. Mites were the most constant and 

were more or less abundant in all the deformations; frequently a minute 

Diplopodon belonging to the genus Polyxenus was also met with. 

Zopf came to the conclusion that the gall-formation was mainly due to 

the mites: they eat out the medulla and possibly through some chemical 

1 Porter 1917. 

2 Friedrich 1906. Waite 1893. 

4 Lesdain 1912. 

5 

Zopf 1907.

GALL-FORMATION 271 

irritation excite the algal zone and cortex to more active growth, so that an 

extensive tangential development takesplace. The small spiders mayexercise 

the same power; evidently the larger holes were formed by them. 

Later Zopf added to gall-deformed plants Ramalina scopnlorum van in- 

crassata and R. cuspidata var. crassa. He found in the- hollow swollen fronds 

abundant evidence of mites, but whether identical with those that attacked 

R. Kullensis could not be determined. These two Ramalinae are maritime 

species ; they are morphologically identical, as are also the deformed varieties, 

and the presence of mites, excreta, etc., are plainly visible in our British 

specimens. 

Bouly de Lesdain 1 found evidence of mite action in Ramalina farinacea 

collected from Pinus sylvestris on the dunes near Dunkirk. The cortex 

had been eaten off either by mites or by a small mollusc (Pupa muscorum] 

and the fronds had collapsed to a more or less convex compact mass. 

Somewhat similar deformations, though less pronounced, were observed in 

other Ramalinae. 

In Cladonia sylvatica and also in Cl. rangiformis Lesdain has indicated 

ff. abortiva Harm, as evidently the result of insect attack. In both cases the 

tips of the podetia are swollen, brown, bent and shrivelled. 

One of the most curious and constant effects, also worked out by Lesdain, 

occurs in Physcia hispida (Ph. stellaris var. tenella). In that lichen the 

gonidia at the tips of the fronds are scooped out and eaten by mites, so 

that the upper cortex becomes separated from the lower part of the thallus. 

As the hyphae of the cortex continue to develop, an arched hood is formed 

of a whitish shell-like appearance and powdery inside. Sometimes the 

mites penetrate at one point only, at other times the attack is at several 

places which may ultimately coalesce into one large cavity. In a crustaceous 

species, Caloplaca (Placodium) citrina he found constant evidence of the 

disturbing effect of the small creatures, which by their action caused the 

areolae of the thallus to grow into minute adherent squamules. A patho- 

logical variety, which he calls var. sorediosa, is distinguished by the presence 

of cup-like hollows which are scooped out by Acarinae and are filled by 

yellowish soredia. In another form, var. maritima, the margins of the areolae, 

occasionally the whole surface, become powdery with a citrine yellow 

efflorescence as a result of their nibbling. 

Zukal 2 adds to the deformations due to organic agents, the hypertrophies 

and abnormalities caused by climatic conditions. He finds such irregularities 

of structure more especially developed in countries with a very limited rain- 

fall, as in certain districts of Chili, Australia and Africa, where changes in 

cortex and rhizoids and proliferations of the thallus testify to the disturbance 

of normal development. 


2 Zukal 1896, p. 258.

CHAPTER VII 

PHYLOGENY 

I. GENERAL STATEMENT 

A. ORIGIN OF LICHENS 

THOUGH lichens are very old members of the vegetable kingdom, as 

symbiotic plants they yet date necessarily from a time subsequent to the 

evolution of their component symbionts. Phylogeny of lichens begins with 

symbiosis. 

The algae, which belong to those families of Chlorophyceae and Myxophyceae 

that live on dry land, had become aerial before their association 

with fungi to form lichens. They must have been as fully developed then 

as now, since it is possible to refer them to the genus or sometimes even to 

the species of free-living forms. The fungus hyphae have combined with a 

considerable number of different algae, so that, even as regards the algal 

symbiont, lichens are truly polyphyletic in origin. 

The fungus is, however, the dominant partner, and the principal line of 

development must be traced through it, as it provides the reproductive organs 

of the plant. Representatives of two great groups of fungi are associated 

with lichens: Basidiomycetes, found in only a few genera, and Ascomycetes 

which form with the various algae the great bulk of lichen families. In 

respect of their fungal constituents lichens are also polyphyletic, and more 

especially in the Ascolichens which can be traced back to several starting 

points. But though lichens have no common origin, the manner of life is 

common to them all and has influenced them all in certain directions: they 

are fitted for a much longer existence than that of the fungi from which they 

started; and both the thallus and the fruiting bodies at least in the sub- 

class Ascolichens can persist through great climatic changes, and can pass 

unharmed through prolonged periods of latent or suspended vitality. 

Another striking note of similarity that runs through the members of this 

sub-class, with perhaps the exception of the gelatinous lichens, is the formation 

of lichen-acids which are excreted by the fungus. These substances are 

peculiar to lichens and go far to mark their autonomy. The production of 

the acids and the many changes evolved in the vegetative thallus suggest the 

great antiquity of lichens.

ORIGIN OF LICHENS 273 

B. ALGAL ANCESTORS 

It is unnecessary to look far for the algae as they have persisted through 

the ages in the same form both without and within the lichen thallus. By 

many early lichenologists the free-living algae, similar in type to lichen algae, 

were even supposed to be lichen gonidia in a depauperate condition and 

were, for that reason, termed by Wallroth " unfortunate brood-cells." In the 

condition of symbiosis they may be considerably modified, but they revert 

to their normal form, and resume their normal life-history of spore production, 

etc., under suitable and free culture. The different algae taking part in 

lichen-formation have been treated in an earlier chapter 1 

. 

C. FUNGAL ANCESTORS 

a. HVMENOLICHENS. The problem of the fungal origin in this sub-class 

is comparatively simple. It contains but three genera of tropical lichens which 

are all associated with Myxophyceae, and the fungus in them, to judge from 

the form and habit of the plants, is a member of the Thelephoraceae. It 

may be that Hymenolichens are of comparatively recent origin and that the 

fungi belonging to the Basidiomycetes had, in the course of time, become 

less labile and less capable of originating a new method of existence. What- 

ever the reason, they lag immeasurably behind Ascomycetes in the formation 

of lichens. 

b. ASCOLICHENS. Lichens are again polyphyletic within this sub-class. 

The main groups from which they are derived are evident. Whether there 

has been a series of origins within the different groups or a development 

from one starting point in each it would be difficult to determine. In any 

case great changes have taken place after symbiosis became established. 

The main divisions within the Ascolichens are related to fungi thus: 

Series I. Pyrenocarpineae I 

. \ to Pyrenomycetes. 

2. Comocarpmeae ) 

3. Graphidineae to Hysteriaceae. 

4. Cyclocarpineae to Discomycetes. 

II. THE REPRODUCTIVE ORGANS 

A. THEORIES OF DESCENT IN ASCOLICHENS 

It has been suggested that ascomycetous fungi, from which Ascolichens 

are directly derived, are allied to the Florideae, owing to the appearance of 

a trichogyne in the carpogonium of both groups. That organ in the red sea- 

weeds is a long delicate cell in direct communication with the egg-cell of 

the carpogonium. It is a structure adapted to totally submerged conditions, 

and fitted to attach the floating spermatia. 

S.L. 

1 See p. 51. 

18

274 

PHYLOGENY 

In fungi there is also a structure considered as a trichogyne 1 

, which, in 

the Laboulbeniales, is a free, simple or branching organ. There is no other 

instance of any similar emergent cell or cells connected with the ascogonium 

of the Ascomycetes, though the term has been applied in these fungi to 

certain short hyphal branches from the ascogonium which remain embedded 

in the tissue. In the Ascomycetes examined all traces of emergent receptive 

in some few there are 

organs, if they ever existed, have now disappeared ; 

ipossible 

internal survivals which never reach the surface. 

In Ascolichens, on the contrary, the "trichogyne," a septate hyphal 

branch extending upwards from the ascogonium, and generally reaching the 

open, has been demonstrated in all the different groups except, as yet,- in 

the Coniocarpineae which have not been investigated. Its presence is a 

strong point in the argument of those who believe in the Floridean ancestry 

of the Ascomycetes. It should be clearly borne in mind that Ascolichens 

are evolved from the Ascomycetes: these latter stand between them and 

any more remote ancestry. 

In the Ascomycetes, there is a recognized progression of development 

in the form of the sporophore from the closed perithecium of the Pyreno- 

mycetes and possibly through the vHysteriaceae, which are partially closed, 

to the open ascocarp of the Discomycetes. If the fungal and lichenoid 

" trichogyne " is homologous with the carpogonial organ in the Florideae, 

then it must have been retained in all the groups of Ascomycetes as an 

emergent structure, and as such passed on from them to their lichen 

derivatives. Has that organ then disappeared from fungi since symbiosis 

began ? There is no trace of it now, except as already stated in Laboulbeniales 

with which lichens are unconnected. 

Were Ascolichens monophyletic in origin, one could more easily suppose 

that both the fungal and lichen series might have started at some early stage 

from a common fungal ancestor possessing a well-developed trichogyne 

which has persisted in lichens, but has been reduced to insignificance in 

fungi, while fruit development proceeded on parallel lines in both. There is 

no evidence that such progression has taken place among lichens the ; theory 

of a polyphyletic origin for the different series seems to be unassailable. At 

the same time, there is no evidence to show in which series symbiosis started 

first. 

It is more reasonable to accept the polyphyletic origin, as outlined above, 

from forms that had already lost the trichogyne, if they ever really possessed 

it, and to regard the lichen trichogyne as a new organ developing in lichens 

in response to some requirement of the deep-seated ascogonium. Its sexual 

function still awaits satisfactory proof, and it is wiser to withhold judgment 

as to the service it renders to the developing fruit. 

1 See p. \li et seq.


B. RELATION OF LICHENS TO FUNGI 

a. PYRENOCARPINEAE. In Phycolichens (containing blue-green gonidia) 

and especially in the gelatinous forms, fructification is nearly always a more 

or less open apothecium. The general absence of the perithecial type is 

doubtless due to the gelatinous consistency of the vegetative structure; it is 

by the aid of moisture that the hymenial elements become turgid enough 

to secure the ejection of the spores through the narrow ostiole of the perithecium, 

and this process would be frustrated were the surrounding and 

enveloping thallus also gelatinous. There is only one minutely foliose or 

fruticose gelatinous family, the Pyrenidiaceae, in which Pyrenomycetes are 

established, and the gonidia, even though blue-green, have lost the gelatinous 

sheath and do not swell up. 

In Archilichens (with bright-green gonidia), perithecial fruits occur 

frequently ; they are nearly always simple and solitary; in only 

a few families 

with a few representatives, is there any approach to the stroma formation so 

marked among fungi. The single perithecium is generally semi-immersed 

in the thallus. It may be completely surrounded by a hyphal " entire " wall, 

either soft and waxy or dark coloured and somewhat carbonaceous. In 

numerous species the outer protective wall covers only the upper portion 

that projects beyond the thallus, and such a perithecium is described as 

" 

dimidiate," a type of fruit occurring in several genera, though rare among 

fungi. 

As to internal structure, there is a dissolution and disappearance of the 

paraphyses in some genera, their protective function not being so necessary 

in closed fruits, a character paralleled in fungi. There is a great variety of 

spore changes, from being minute, simple and colourless, to varied septation, 

general increase in size, and brown colouration. The different types may 

be traced to fungal ancestors with somewhat similar spores, but more 

generally they have developed within the lichen series. From the life of the 

individual it is possible to follow the course of evolution, and the spores of 

all species begin as simple, colourless bodies; in some genera they remain 

so, in others they undergo more or less change before reaching the final 

stage of colour or septation that marks the mature condition. 

As regards direct fungal ancestors, the Pyrenocarpineae, with solitary 

perithecia, are nearest in fruit structure to the Mycosphaerellaceae, in which 

family are included several fungus genera that are parasitic on lichens such 

as Ticothecium, Mullerella, etc. In that family occurs also the genus Stigmatea, 

in which the perithecia in form and structure are very similar to dimidiate 

Vernicariae. 

Zahlbruckner 1 has suggested as the starting point for the Verrucariaceae 


18 2

276 

PHYLOGENY 

the fungus genus Verrncula. It was established by Steiner 1 to include two 

species, V. cahirensis and V. aegyptica, their perithecia being exactly similar 

to those of Verrucaria? in which genus they were originally placed. Both 

are parasitic on species of Caloplaca (Placodium}. The former, on C. gilvella, 

transforms the host thallus to the appearance of a minutely lobed Placodium ; 

the latter occupies an island-like area in the centre of the thallus of Caloplaca 

interveniens, and gives it, with its accompanying parasite, the character of 

an Endopyrenium (Dermatocarpon), while the rest of the thallus is normal 

and fertile. 

Zahlbruckner may have argued rightly, but it is also possible to regard 

these rare desert species as reversions from an originally symbiotic to a purely 

parasitic condition. Reinke came to the conclusion that if a parasitic 

species were derived directly from a lichen type, then it must still rank as 

a lichen, a view that has a direct bearing on the question. The parallel 

family of Pyrenulaceae which have Trentepohlia gonidia is considered by 

Zahlbruckner to have originated from the fungus genus Didymella. 

Compound or stromatoid fructifications occur once and again in lichen 

3 

families; but, according to Wainio , there is no true stroma formation, only 

a pseudostroma resulting from adhesions and agglomerations of the thalline 

envelopes or from cohesions of the margins of developing fruit bodies. 

These pseudostromata are present in the genera Chiodecton and Glyphis 

(Graphidineae) and in Trypethelium, Mycoporium, etc. (Pyrenocarpineae). 

This view of the nature of the compound fruits is strengthened, as Wainio 

points out, by the presence in certain species of single apothecia or perithecia 

on the same specimen as the stromatoid fruits. 

b. CONIOCARPINEAE. This subseries is entirely isolated. Its peculiarity 

lies in the character of the mature fruit in which the spores, owing to the 

early breaking down of the asci, lie as a loose mass in the hymenium, while 

dispersal is delayed for an indefinite time. This type of fruit, termed a 

mazaedium by Acharius, is in the form of a stalked or sessile roundish head 

the capitulum closed at first and only half-open at maturity rarely, as in 

Cyphelium, an exposed disc. There is a suggestion, but only a suggestion, of a 

similar fructification in the tropical fungus Camillea in which there is some- 

times a stalk with one or more perithecia at the tip, and in some species early 

disintegration of the asci, leaving spore masses 4 . But neither in fungi nor in 

other lichens is there any obvious connection with Coniocarpineae. In some 

of the genera the fungus alone forms the stalk and the wall of the capitulum ; 

in others the thallus shares in the fruit-formation growing around it as an 

amphithecium. 

The semi-closed fruits point to their affinity with Pyrenolichens, though 

1 Steiner 1896. 

2 

Muller-Argau 1880. 

3 Wainio 1890, p. xxiii. 

4 

Lloyd 1917.


they are more advanced than these judging from the thalline wall that is 

present in some genera and also from the half-open disc at maturity. The 

latter feature has influenced some systematists to classify the whole subseries 

among Cyclocarpineae. The thallus, as in Sphaerophorus, reaches a high 

degree of fruticose development ; in other genera it is crustaceous without 

any formation of cortex, while in several genera or species it is non-existent, 

the fruits being parasites on the thalli of other lichens or saprophytes on 

dead wood, humus, etc. These latter both parasites and saprophytes 

are included by Rehm 1 and others among fungi, which has involved the 

breaking up of this very distinctive series. Rehm has thus published as 

Discomycetes the lichen genera Sphinctrina, Cyphelium, Coniocybe, Ascoliunit 

Calicium and Stenocybe, since some or all of their species are regarded by 

him as fungi. 

Reinke 2 in his lichen studies states that it might not be impossible for 

a saprophytic fungus to be derived from a crustaceous lichen a case of 

reversion but that no such instance was then known. More exact studies 3 

of parasymbiosis and antagonistic symbiosis have shown the wide range of 

possible life-conditions, and such a reversion does not seem improbable. We 

must also bear in mind that in suitable cultures, lichen hyphae can be grown 

without gonidia: they develop in that case as saprophytes. 

On Reinke's 2 

view, however, that these saprophytic species, belonging to 

different genera in the Coniocarpineae, are true fungi, they would represent 

the direct and closely related ancestors of the corresponding lichen genera, 

giving a polyphyletic origin within this group. As fungus genera he has 

united them in Protocaliciaceae, and the representatives among fungi he 

distinguishes, 

Mycocon iocybe. 

as does Wainio 4 

, under such names as Mycocalicium and 

If we might consider the saprophytic forms as also retrogressive lichens, 

a monophyletic origin from some remote fungal ancestor would prove a more 

satisfactory solution of the inheritance problem. This view is even supported 

by a comparison Reinke himself has drawn between the development of the 

fructification in Mycocalicium parietinum, a saprophyte, and in his view a 

fungus, and Chaenotheca cJirysocephala, a closely allied lichen. Both grow on 

old timber. In the former (the fungus), the mycelium pervades the outer 

weathered wood-cells, and the fruit stalk rises from a clump of brownish 

hyphae; there is no trace of gonidia. ChaenotJieca chrysocephala differs in the 

in scattered 

presence of gonidia which are associated with the mycelium 

granular warts; but the fruit stalk here also rises directly from the mycelium 

between the granules. The presence of a lichen thallus chiefly differentiates 

between the two plants, and this thallus is not a casual or recent association; 

it is constant and of great antiquity as it is richly provided with lichen-acids. 

1 Rehm 1890. 


3 See p. 260. 

4 Wainio 1890.

2;8 

PHYLOGENY 

Reinke has indicated the course of evolution within the series but that 

and will be considered later. 

is on the lines of thalline development 

c. GRAPHIDINEAE. This series contains a considerable variety of lichen 

forms, but all possess to a more or less marked degree the linear form of 

fructification termed a "lirella" which has only a slit-like opening. There 

is a tendency to round discoid fruits in the Roccellae and also in the Arthoniae; 

the apothecia of the latter, called by early lichenologists "ardellae," are with- 

out margins. In nearly all there is a formation of carbonaceous black tissue 

either in the hypothecium or in the proper margins. In some of them the 

paraphyses are branched and dark at the tips, the branches interlocking to 

form a strong protective epithecium. There are, however, constant exceptions, 

in some particular, to any generalization in genera and in species. Miiller- 

Argau's 1 

pronouncement might be held to have special reference to Graphidineae: 

"that in any genus, species or groups of species are to be found 

which outwardlyshew something that is peculiar, thoughof slightimportance." 

The most constant type of gonidium is Trentepbhlia, but Palmella and 

Phycopeltis occasionally occur. The spores are various in colour and form ; 

they are rarely simple. 

The genus Arthonia is derived from a member of the Patellariaceae, from 

which family many of the Discomycetes have arisen. The course of development 

does not follow from a closed to an open fruit ; 

the apothecium is open 

from the first, and growth proceeds from the centre outwards, the fertile cells 

gradually pushing aside the sterile tissue of the exterior. The affinity of 

Xylographa (with Palmella gonidia) is to be found in Stictis in the fungal 

family Stictidaceae, the apothecia of Stictis being at first closed, then open, 

and with a thick margin ; Xylographa has a more elongate lirella fruit, though 

otherwise very similar, and has a very reduced thallus. Rehm 2 has classified 

Xylographa as a fungus. 

The genera with linear apothecia are closely connected with Hysteriaceae, 

and evidently inherit their fruit form severally from that family. There is 

thus ample evidence of polyphyletic descent in the series. Stromatoid fruits 

occur in Chiodectonaceae, with deeply sunk, almost closed disc, but they 

have evidently evolved within the series, possibly from a dividing up of the 

lirellae. 

In Graphidineae there are also forms, more especially in Arthoniaceae, 

on the border line between lichens and fungi: those with gonidia being 

classified as lichens, those without gonidia having been placed in corre- 

sponding genera of fungi. These latter athalline species live as parasites or 

saprophytes. 

The larger number of genera have a poorly developed thallus; in many 

of them it is embedded within the outer periderm-cells of trees, and is known 

1 

Muller-Argau 1862. 2 Rehm 1890.


as " 

hypophloeodal." But in some families, such as Roccellaceae, the thallus 

attains a very advanced form and a very high production of acids. 

The conception of Graphidineae as a whole is puzzling, but one or other 

characteristic has brought the various members within the series. It is in 

this respect an epitome of the lichen class of which the different groups, 

with all their various origins and affinities, yet form a distinct and well-defined 

section of the vegetable kingdom. 

d. CYCLOCARPINEAE. This is by far the largest series of lichens. The 

genera are associated with algae belonging both to the Myxophyceae and 

the Chlorophyceae, and from the many different combinations are produced 

great variations in the form of the vegetative body. The fruit is an emergent, 

round or roundish disc or open apothecium in all the members of the series 

except Pertusariaceae, where it is partially immersed in thalline " warts." 

In its most primitive form, described as "biatorine" or "lecideine," it may 

be soft and waxy {Biatorci) or hard and carbonaceous (Lecidea), in the latter 

the paraphyses being mostly coloured at the tips ; 

these are either simple or 

but sparingly branched, so that the epithecium is a comparatively slight 

structure. The outer sterile tissue forms a protective wall or "proper margin" 

which may be entirely pushed aside, but generally persists as a distinct rim 

round the disc. 

A great advance within the series arose when the gonidial elements of 

the thallus took part in fruit-formation. In that case not only is the 

hymenium generally subtended by a layer of algae, but thalline tissue containing 

algae grows up around the fruit, and forms a second wall or thalline 

margin. This type of apothecium, termed " lecanorine," is thus intimately 

associated with the assimilating tissue and food supply, and it gains in 

capacity of ascus renewal and of long duration. This development from 

non-marginate to marginate ascomata is necessarily an accompaniment of 

symbiosis. 

There is no doubt that the Cyclocarpineae derive from some simple 

form or forms of Discomycete in the Patellariaceae. The relationship 

between that family and the lower Lecideae is very close. Rehm 1 finds the 

direct ancestors of Lecidea itself in the fungus genus, Patinella, in which the 

apothecia are truly lecideine in character open, flat and slightly margined, 

the hypothecium nearly always dark-coloured and the paraphyses branched, 

septate, clavate and coloured at the tips, forming a dark epithecium. More 

definitely still he describes Patinella atroviridis, a new species he discovered, 

as in all respects a Lecidea, but without gonidia. 

In the crustaceous Lecideaceae, a number of genera have been delimited 

on spore characters colourless or brown, and simple or variously septate. 

In Patellariaceae as described by Rehm are included a number of fungus 

1 Rehm 1890.

2 8o 

PHYLOGENY 

genera which correspond to these lichen genera. Only two of them 

Patinella and Patellaria are saprophytic ; in all the other genera of the 

family, the species with very few exceptions are parasitic on lichens : they 

are parasymbionts sharing the algal food supply ; in any case, they thrive 

on a symbiotic thallus. 

Rehm unhesitatingly derives the corresponding lichen genera from these 

fungi. He takes no account of the difficulty that if these parasitic (or saprophytic) 

fungi are primitive, they have yet appeared either later in time than 

the lichens on which they exist, or else in the course of ages they have 

entirely changed their substratum. 

He has traced, for instance, the lichen, Buellia, to a saprophytic fungus 

species, Karschia lignyota, to a genus therefore in which most of the species 

are parasitic on lichens and have generally been classified as parasitic lichens. 

There is no advance in apothecial characters from the fungus, Karschia, to 

Buellia, merely the change to symbiosis. It therefore seems more in accordance 

with facts to regard Buellia as a genus evolved within the lichen series 

from Patinella through Lecidea, and to accept these species of Karschia on 

the border line as parasitic, or even as saprophytic, reversions from the 

lichen status. We may add that while these brown-spored lichens are fairly 

abundant, the corresponding athalline or fungus forms are comparatively 

few in number, which is exactly what might be expected from plants with 

a reversionary history. 

Occasionally in biatorine or lecideine species with a slight thalline 

development all traces of the thallus disappear after the fructification has 

reached maturity. The apothecia, if on wood or humus, appear to be 

saprophytic and would at first sight be classified as fungi. They have un- 

or in certain con- 

doubtedly retained the capacity to live at certain stages, 

ditions, as saprophytes. 

The thallus disappears also in some species of the crustaceous genera 

that possess apothecia with a thalline margin, and the fruits may be left 

stranded and solitary on the normal substratum, or on some neighbouring 

lichen thallus where they are more or less parasitic ; but as the thalline 

margin persists, there has been no question as to their nature and affinity. 

Rehm suggests that many species now included among lichens may be 

ultimately proved to be fungi ; but it is equally possible that the reverse may 

be the case, as for instance Bacidiaflavovirescens, held by Rehm and others to 

be a parasitic fungus species, but since proved by Tobler 1 

2 

A note by Lightfoot , 

to be a true lichen. 

one of our old-time botanists who gave lichens a 

considerable place in his Flora, foreshadows the theory of evolution by 

gradual advance, and his views offer a suggestive commentary on the subject 

under discussion. He was debating the systematic position of the maritime 

1 Tobler 191 1 2 , p. 407. 

2 

Lightfoot 1777, p. 965.


lichen genus Lichina, considered then a kind of Fucus, and had observed 

its similarity with true lichens. 

" The " 

cavity," he writes, at the top of the 

fructification (in Lichind) is a proof how nearly this species of Fucus is 

related to the scutellated lichens. Nature disdains to be limited to the 

systematic rules of human invention. She never makes any sudden starts 

from one class or genus to another, but is regularly progressive in all her 

works, uniting the various links in the chain of beings by insensible con- 

nexions." 

III. THE THALLUS 

A. GENERAL OUTLINE OF DEVELOPMENT 

a. PRELIMINARY CONSIDERATIONS. The evolution of lichens, as such, 

has reference mainly to the thallus. Certain developments of the fructification 

are evident, but the changes in the reproductive organs have not kept pace 

with those of the vegetative structures: the highest type of fruit, for instance, 

the apothecium with a thalline margin, occurs in genera and species with a 

very primitive vegetative structure as well as in those that have attained 

higher development. 

Lichens are polyphyletic as regards their algal, as well as their fungal, 

ancestors, so that it is impossible to indicate a straight line of progression, 

but there is a general process of thalline development which appears once 

and again in the different phyla. That process, from simpler to more com- 

plicated forms, follows on two lines: on the one there is the endeavour to 

increase the assimilating surface, on the other the tendency to free the plant 

from the substratum. In both, the aim has been the same, to secure more 

favourable conditions for assimilation and aeration. Changes 

have been already described 1 

lines of evolution. 

in structure 

, and it is only needful to indicate here the main 

b. COURSE OF EVOLUTION IN HYMENOLICHENS. There is but little 

trace of development in these lichens. The fungus has retained more or less 

the form of the ancestral Thelephora which has a wide-spreading superficial 

basidiosporous hymenium. Three genera have been recognized, the differences 

between them being due to the position within the thallus, and the form of 

the Scytonema that constitutes the gonidium. The highest stage of development 

and of outward form is reached in Cora, in which the gonidial zone 

is central in the tissue and is bounded above and below by strata of hyphae. 

c. COURSE OF EVOLUTION IN ASCOLICHENS. It is in the association 

with Ascomycetes that evolution and adaptation have had full scope. In 

that subclass there are four constantly recurring and well-marked stages 

of thalline development, (i) The earliest, most primitive stage, is the 

1 See Chap. III.

282 PHYLOGENY 

crustaceous: at first an accretion of separate granules which may finally be 

united into a continuous crust with a protective covering of thick-walled 

amorphous hyphae forming a " decomposed " cortex. The extension of 

a granule by growth in one direction upwards and outwards gives detachment 

from the substratum, and originates (2) the squamule which is, how- 

ever, often of primitive structure and attached to the support, like the granule, 

by the medullary hyphae. Further growth of the squamule results in (3) 

the foliose thallus with all the adaptations of structure peculiar to that form. 

In all of these, the principal area of growth is round the free edges of the 

thallus. A greater change takes place in the advance to (4) the fruticose 

type in which the more active growing tissue is restricted to the apex, and 

in which the frond or filament adheres at one point only to the support, a 

new series of strengthening and other structures being evolved at the same 

time. 

The lichen fungi associate, as has been already stated, with two different 

types of algae: those combined with the Myxophyceae have been designated 

Phycolichenes, those with Chlorophyceae as Archilichenes. The latter predominate, 

not only in the number of lichens, but also in the more varied 

advance of the thallus, although, in many instances, genera and species of 

both series may be closely related. 

B. COMPARATIVE ANTIQUITY OF ALGAL SYMBIONTS 

One of the first questions of inheritance concerns the comparative an- 

tiquity of the two gonidial series: with which kind of alga did the fungus 

first form the symbiotic relationship ? No assistance in solving the problem 

is afforded by the type of fructification. The fungus in Archilichens is 

frequently one of the more primitive Pyrenomycetes, though more often a 

Discomycete, while in Phycolichens Pyrenomycetes are very rare. There 

is, as already stated, no corelation of advance between the fruit and the 

thallus, as the most highly evolved apothecia with well-formed thalline 

margins are constantly combined with thalli of low type. 

Forssell 1 

gave considerable attention to the question of antiquity in his 

study of gelatinous crustaceous lichens in the family Pyrenopsidaceae, termed 

by him Gloeolichens, and he came to the conclusion that Archilichens 

represented the older combination, Phycolichens being comparatively.young. 

His view is based on a study of the development of certain lichen fungi 

that seem able to adapt themselves to either kind of algal symbiont. He 

found 1 in Euopsis (Pyrenopsis) granatina, one of the Pyrenopsidaceae, that 

certain portions of the thallus contained blue-green algae, while others con- 

tained Palmella, and that these latter, though retrograde in development, 

1 Forssell 1885.

THE THALLUS 283 

might become fertile. The granules with blue-green gonidia were stronger, 

more healthy and capable of displacing those with Palmella, but not of 

bearing apothecia, though spermogonia were embedded in them a first step, 

according to Forssell, towards the formation of apothecia. These granules, 

not having reached a fruiting stage, were reckoned to be of a more recent 

type than those associated with Palmella. In other instances, however, the 

line of evolution has been undoubtedly from blue-green to more highly 

evolved bright-green thalli. 

The striking case of similarity between Psoroma hypnorum (bright-green) 

and Pannaria rubiginosa (blue-green) may also be adduced. Forssell con- 

siders that Psoroma is the more ancient form, but as the fungus is adapted 

to associate with either kind of alga, the type of squamules forming the 

thallus may be gradually transformed by the substitution of blue-green for 

the earlier bright-green the Pannaria superseding the Psoroma. There is 

a close resemblance in the fructification that is of the fungus in these two 

different lichens. 

Hue 1 shares Forssell's opinion as to the greater antiquity of the bright- 

green gonidia and cites the case of Solorina crocea. In that lichen there is 

a layer of bright-green gonidia in the usual dorsiventral position, below the 

of blue- 

upper cortex. Below this zone there is a second formed entirely 

green cells. Hue proved by his study of development in Solorina that the 

bright-green were the normal gonidia of the thallus, and were the only ones 

present in the growing peripheral areas; the blue-green were a later addition, 

and appeared first in small groups at some distance from the edge of the 

lobes. 

The whole subject of cephalodia-development 2 has a bearing on this 

question. These bodies always contain blue-green algae, and are always 

associated with Archilichens. Mostly they occur as excrescences, as in 

Stereocaulon and in Peltigera. The fungus of the host-lichen though normally 

adapted to bright-green algae has the added capacity of forming later a symbiosis 

with the blue-green. This tendency generally pervades a whole genus 

or family, the members of which, as in Peltigeraceae, are too closely related 

to allow as a rule of separate classification even when the algae are totally 

distinct. 

C. EVOLUTION OF PHYCOLICHENS 

The association of lichen-forming fungi with blue-green algae may have 

taken place later in time, or may have been less successful than with the 

bright-green: they are fewer in number, and the blue-green type of thallus 

is less highly evolved, though examples of very considerable development 

are to be found in such genera as Peltigera, Sticta or Nephromium. 

1 Hue 191 1 1 . 

2 See p. 133.

284 

PHYLOGENY 

a. GLOEOLICHENS. Among crustaceous forms the thallus is generally 

elementary, more especially in the Gloeolichens (Pyrenopsidaceae). The 

algae of that family, Gloeocapsa, Xanthocapsa or Chroococcus, are furnished 

with broad gelatinous sheaths which, in the lichenoid state, are penetrated 

and traversed by the fungal filaments, a branch hypha generally touching 

with its tip the algal cell-wall. Under the influence of symbiosis, the algal 

masses become firmer and more compact, without much alteration in form; 

algae entirely free from hyphae are often intermingled with the others. Even 

among Gloeolichens there are signs of advancing development both in the 

internal structure and in outward form. Lobes free from the substratum, 

though very minute, appear in the genus Paulia, the single species of which 

comes from Polynesia. Much larger lobes are characteristic of Thyrea, a 

Mediterranean and American genus. The fruticose type, with upright fronds 

of minute size, also appears in our native genus Synalissa. It is still more 

marked in the coralloid thalli of Peccania and Phleopeccania. In most of 

these genera there is also a distinct tendency to differentiation of tissues, 

with the gonidia congregating towards the better lighted surfaces. The only 

cortex formation occurs in the crustaceous genus Forssellia in which, according 

to Zahlbruckner 1 

, it is plectenchymatous above, the thallus being attached 

below by hyphae penetrating the substratum. In another genus, Anema?, 

which is minutely lobate-crustaceous, the internal hyphae form a cellular 

network in which the algae are immeshed. As regards algal symbionts, 

the members of this family are polyphyletic in origin. 

b. EPHEBACEAE AND COLLEMACEAE. In Ephebaceae the algae are 

tufted and filamentous, Scytonema, Stigonema or Rivularia, the trichomes of 

which are surrounded by a common gelatinous sheath. The hyphae travel 

in the sheath alongside the cell-rows, and the symbiotic plant retains the 

tufted form of the alga as in Lichina with Rivularia, Leptogidium with Scytonema, 

and Ephebe with Stigonema. The last named lichen forms a tangle of 

intricate branching filaments about an inch or more in length. The fruticose 

habit in these plants is an algal characteristic ; it has not been acquired as a 

result of symbiosis, and does not signify any advance in evolution. 

A plectenchymatous cortex marks some progress here also in Leptodendriscum, 

Leptogidium and Polychidium, all of which are associated with 

Scytonema. These genera may well be derived from an elementary form 

such as Thermutis. They differ from each other in spore characters, etc., 

Polychidium being the most highly developed 

with its cortex of two cell- 

rows and with two-celled spores. 

Nostoc forms the gonidium of Collemaceae. In its free state it is extremely 

gelatinous and transmits that character more or less to the lichen. In the 

crustaceous genus Physma, which forms the base of the Collema group or 


2 Reinke 1895.


there is but little difference in form between the thalline warts of 

phylum, 

the lichen crust and the original small Nostoc colonies such as are to be 

found on damp mosses, etc. 

In Collema itself, the less advanced species are scarcely more than crusts, 

though the more developed show considerable diversity of lobes, either short 

and pulpy, or spreading out in a thin membrane. The Nostoc chains pervade 

the homoiomerous thallus, but in some species they lie more towards the 

upper surface. There is no cortex, though once and again plectenchyma 

appears in the apothecial margin, both in this genus and in Leprocolletna 

which is purely crustaceous. 

Leptogium is a higher type than Col/etna, the thallus being distinguished 

by its cellular cortex. The tips of the hyphae, lying close together at the 

surface, are cut off by one or more septa, giving a one- or several-celled 

cortical layer. The species though generally homoiomerous are of thinner 

texture and are less gelatinous than those of Collema. 

c. PVRENIDIACEAE. This small family of pyrenocarpous Phycolichens 

may be considered here though its affinity, through the form of the fruiting 

body, is with Archilichens. The gonidia are species of Nostoc, Scytoncma 

and Stigonema. There are only five genera; one of these, Eolichcn, contains 

three species, the others are monotypic. 

The crustaceous genera have a non-corticate thallus, but an advance to 

lobate form takes place in PlacotJielium, an African genus. The two genera 

that show most development are both British: Corisciiun (Normandina), 

which is lobate, heteromerous and corticate though always sterile and 

Pyreniciium which is fruticose in habit ; the latter is associated with Nostoc 

and forms a minute sward of upright fronds, corticate all round ; the peri- 

thecium is provided with an entire wall and is immersed in the thallus. 

If the thallus alone were under consideration these lichens would rank 

with Pannariaceae. 

d. HEPPIACEAE AND PANNARIACEAE. The next stage in the develop- 

ment of Phycolichens takes place through the algae, Scytonema and Nostoc, 

losing not only their gelatinous sheaths, but also, to a large extent, their 

characteristic forms. Chains of cells can frequently be observed, but accurate 

and certain identification of the algal genus is only possible by making 

separate cultures of the gonidia. 

Scytonema forms the gonidium of the squamulose Heppiaceae consisting 

of the single genus Heppia. The ground tissue of the species is either 

wholly of plectenchyma with algae in the interstices, or the centre is occupied 

a narrow medulla of loose filaments. 

by 

In the allied family Pannariaceae, a number of genera contain Scytonema 

or Nostoc, while two, Psoroma and Psoromaria, have bright-green gonidia.

286 

PHYLOGENY 

The thallus varies from crustaceous or minutely squamulose, to lobes of 

fair dimension in Parmeliella and in Hydrothyria venosa, an aquatic lichen. 

Plectenchyma appears in the upper cortex of both of these, and in the 

proper margin of the apothecia, while the under surface is frequently provided 

' 

with rhizoidal filaments. 

These two families form a transition between the gelatinous, and mostly 

homoiomerous thallus, and the more developed entirely heteromerous thallus 

of much more advanced structure. The fructification in all of them, gelatinous 

and non-gelatinous, is a more or less open apothecium, sometimes immar- 

ginate, and biatorine or lecideine, but often, even in species nearly related 

to these, it is lecanorine with a thalline amphithecium. Rarely are the spori- 

ferous bodies sunk in the tissue, with a pseudo-perithecium, as in Phylliscum. 

It would be difficult to trace advance in all this group on the lines of fruit 

development. The two genera with bright-green gonidia, Psoroma and 

Psoromaria, have been included in Pannariaceae owing to the very close 

affinity of Psoroma hypnorum with Pannaria rubiginosa; they are alike in 

every respect except in their gonidia. Psoromaria is exactly like Psoroma, 

but with immarginate biatorine apothecia, representing therefore a lower 

development in that respect. 

These lichens not only mark the. transition from gelatinous to non- 

gelatinous forms, but in some of them there is an interchange of gonidia. 

The progression in the phylum or phyla has evidently been from blue-green 

up to some highly evolved forms with bright-green algae, though there may 

have been, at the beginning, a substitution of blue-green in place of earlier 

bright-green algae, Phycolichens usurping as itwerethe Archilichen condition. 

e. PELTIGERACEAE AND STICTACEAE. The two families just examined 

marked a great advance which culminated in the lobate aquatic lichen 

Hydrothyria. This lichen, as Sturgis pointed out, shows affinity with other 

Pannariaceae in the structure of the single large-celled cortical layer as well 

as with species of Nepkroma (Peltigeraceae). A still closer affinity may be 

traced with Peltigera in the presence in both plants of veins on the under 

surface. The capacity of Peltigera species to grow in damp situations may 

also be inherited from a form like the submerged Hydrothyria. In both 

families there are transitions from blue-green to bright-green gonidia, or 

vice versa, in related species. Thus in Peltigeraceae we find Peltigera con- 

taining Nostoc in the gonidial zone, with Peltidea which may be regarded 

as a separate genus, or more naturally as a section of Peltigera; it contains 

bright-green gonidia, but has cephalodia containing Nostoc associated 

its thallus. 

with 

The genus Nephroma is similarly divided into species with a bright-green 

gonidial zone, chiefly Arctic or Antarctic in distribution, and species with 

Nostoc (subgenus Nephromium) more numerous and more widely distributed.


Peltigera and Nephroma are also closely related in the character of the 

fructification. It is a flat non-marginate disc borne on the edge of the 

thallus: in Peltigera on the upper surface, in Nephroma on the under surface. 

The remaining genus Solorina contains normally a layer of bright-green 

algae, but, along with these, there are always present more or fewer Nosloc 

cells, either in a thin layer as in S. crocea or as cephalodia in others, while, 

in three species the algae are altogether blue-green. 

The members of the Peltigeraceae have a thick upper cortex of plectenchyma 

and in some cases strengthening veins, and long rhizinae on the 

lower side. Some of the species attain a large size, and, in some, soredia 

are formed, an evidence of advance, this being a peculiarly lichenoid form 

of reproduction. 

The Stictaceae form a parallel but more highly organized family, which 

also includes closely related bright-green and blue-green series. They are 

all dorsiventral, but they are mostly attached by a single hold-fast and the 

lobes in some species suggest the fruticose type in their long narrow form. 

A wide cortex of plectenchyma protects both the upper and the lower 

surface and a felt of hairs replaces the rhizinae of other foliose lichens. In 

the genus Sticta (including the section Sticlind) special aeration organs, 

in Lobaria these are replaced by 

cyphellae or pseudocyphellae, are provided ; 

naked areas which serve the same purpose. 

regarded the Stictaceae as the most highly developed of all 

Nylander 1 

lichens, and they easily take a high place among dorsiventral forms, but it 

is generally conceded that the fruticose type is the more highly organized. 

In any case they are the highest reach of the phylum or phyla that started 

with Pyrenopsidaceae and Collemaceae ; 

the lowly gelatinous thalli changing 

to more elaborate structures with the abandonment of the gelatinous algal 

sheath, as in the Pannariaceae, and with the replacement of blue-green by 

considers the Stictaceae as evolved from the 

bright-green gonidia. Reinke 2 

, 

Pannariaceae more directly from the genus Massalongia. Their relationship 

is certainly with Pannariaceae and Peltigeraceae rather than with Par- 

meliaceae ; 

these latter, as we shall see, belong to a wholly different series. 

D. EVOLUTION OF ARCHILICHENS 

The study of Archilichens as of Phycolichens is complicated by the 

many different kinds of fungi and algae that have entered into combination ; 

but the two principal types of algae are the single-celled Protococcus group 

and the filamentous Trenlepohtia : as before only the broad lines of thalline 

development will be traced. 

The elementary forms in the different series are of the simplest type a 

somewhat fortuitous association of alga and fungus, which in time bears the 

1 

Seep. 126. 

2 Reinke 1895.

288 

PHYLOGENY 

lichen fructification. It has been stated that the greatest advance of all 

took place with the formation of a cortex over the primitive granule, 

followed by a restricted area of growth outward or upward which resulted 

finally in the foliose and fruticose thalli. Guidance in following the course 

of evolution is afforded by the character of the fructification, which generally 

shows some great similarity of type throughout the different phyla, and 

remains fairly constant during the many changes 

of thalline evolution. 

Development starting from one or many origins advances point by point in 

a series of parallel lines. 

a. THALLUSOF PYRENOCARPINEAE. In this series there are two families 

of algae that function as gonidia: Protococcaceae, consisting of single cells, 

and Trentepohliaceae, filamentous. Phyllactidium (Cephaleuros) appears in 

a single genus, Strigula, a tropical epiphytic lichen. 

Associated with these types of algae are a large number of genera and 

species of an elementary character, without any differentiation of tissue. In 

many instances the thallus is partly or wholly embedded in the substratum. 

Squamulose or foliose forms make theirappearance in Dermatocarpaceae : 

in Normandina the delicate shell-like squamules are non-corticate, but in 

other genera, Endocarpon, Placidiopsis, etc., the squamules are corticate and 

of firmer texture, while in Dermatocarpon, foliose fronds of considerable size 

are formed. The perithecial fruits are embedded in the upper surface. 

In only one extremely rare lichen, Pyrenothamnia Spraguei(N. America), 

is there fruticose development: the thallus, round and stalk-like at the base, 

branches above into broader more leaf-like expansions. 

b. THALLUS OF CONIOCARPINEAE. At the base of this series are genera 

and species that are extremely elementary as regards thalline formation, 

with others that are saprophytic and parasitic. The simplest type of thallus 

occurs in Caliciaceae, a spreading mycelium with associated algae (Proto- 

coccaceae) collected in small scattered granules, resembling somewhat a collection 

of loose soredia. The species grow mostly on old wood, trunks of trees, 

etc. In Calidwn (Chaenothecd) chrysocephalum as described by Neubner 1 the 

first thallus formation begins with these scattered minute granules; gradually 

they increase in size and number till a thick granular coating of the substratum 

arises, but no cortex is formed and there is no differentiation of tissue. 

The genus Cyphelium (Cypheliaceae) is considered by Reinke to be more 

highly developed, inasmuch as the thalline granules, though non-corticate, 

are more extended horizontally, and, in vertical section, show a distinct 

differentiation into gonidial zone and medulla. The sessile fruit also takes 

origin from the thallus, and is surrounded by a thalline amphithecium, or 

rather it remains embedded in the thalline granule. A closely allied tropical 

1 Neubner 1893.


genus Pyrgillus has reached a somewhat similar stage of development, but 

with a more coherent homogeneous thallus, while in Tylophoron, also tropical 

or subtropical, the fruit is raised above the crustaceous thallus but is thickly 

surrounded by a thalline margin. The alga of that genus is Trentepolilia, 

a rare constituent of Coniocarpineae. 

A much more advanced formation appears in the remaining family 

Sphaerophoraceae. In Calycidium, a monotypic New Zealand genus, the 

thallus consists of minute squamules, dorsiventral in structure but with a 

tendency to vertical growth, the upper surface is corticate and the mazaedial 

apothecia always open are situated on the margins. Tlwlurna dissimilis, 

(Scandinavian) still more highly developed, has two kinds of rather small 

fronds corticate on both surfaces, the one horizontal in growth, crenulate in 

outline, and sterile, the other vertical, about 2 mm. in height, hollow and 

terminating in a papilla in which is seated the apothecium. 

Two other monotypic subtropical genera form a connecting link with 

the more highly evolved forms. In the first, Acroscyphus sphaerophoroides, 

the fronds are somewhat similar to the fertile ones of Tholurna, but they 

possess a solid central strand and the apical mazaedium is less enveloped by 

the thallus. The o\\\er,Pleurocybe madagascarea, has narrow flattish branching 

fronds about 3 cm. in height, hollow in the centre and corticate with marginal 

or surface fruits. 

The third genus, Sphaerophorus, is cosmopolitan three of the ; 

species are 

British and are fairly common on moorlands, etc. They 

are fruticose in 

habit, being composed of congregate upright branching stalks, either round 

or slightly compressed and varying in height from about I to 8 cm. The 

structure is radiate with a well-developed outer cortex, and a central strand 

which gives strength to the somewhat slender stalks. The fruits are lodged 

in the swollen tips and are at first enclosed; later, the covering thallus splits 

irregularly and exposes the hymenium. 

Coniocarpineae comprise only a comparatively small number of genera 

and species, but the series is of unusual interest as being extremely well 

defined by the fruit-formation and as representing all the various stages of 

thalline development from the primitive crustaceous to the highly evolved 

fruticose type. With the primitive thallus is associated a wholly fungal 

fruit, both stalk and capitulum, which in the higher forms is surrounded and 

protected by the thallus. Lichen-acids are freely produced even in crustaceous 

forms, and they, along with the high stage of development reached, testify to 

the great antiquity of the series. 

c. THALLUS OF GKAPHIDINEAE. As formerly understood, this series 

included only crustaceous forms with an extremely simple development of 

thallus, fungi and algae whether Palmellaceae, etc., or more frequently 

Trentepohliaceae growing side by side either superficially 

or embedded in 

s. L. '9

290 

PHYLOGENY 

tree or rock, the presence of the vegetative body being often signalled only 

by a deeper colouration of the substratum. The researches of Almquist, 

and more recently of Reinke and Darbishire, have enlarged our conception 

of the series, and the families Dirinaceae and Roccellaceae are now classified 

in Graphidineae. 

Arthoniaceae, Graphidaceae and Chiodectonaceae are all wholly crus- 

taceous. The first thalline advance takes place in Dirinaceae with two allied 

genera, Dirina and Dirinastrum. Though the thallus is still crustaceous, it 

is of considerable thickness, with differentiation of tissues: on the lower 

side there is a loosely filamentous medulla from which hyphae pierce the 

substratum and secure attachment. Trentepokliagomfaa. lie in a zone above 

the medulla, and the upper cortex is formed of regular palisade hyphae 

" 

forming a fastigiate cortex." It is the constant presence of Trentepohlia 

algae as well as the tendency to ellipsoid or lirellate fruits that have influenced 

the inclusion of Dirinaceae and Roccellaceae in the series. 

The thallus of Dirinaceae is crustaceous, while the genera of Roccellaceae 

are mostly of an advanced fruticose type, though in one, Roccellina, there is 

a crustaceous thallus with an upright portion consisting of short swollen 

and in another, Roccello- 

podetia-like structures with apothecia at the tips ; 

grapha, the fronds broaden to leafy expansions. They are nearly all rockdwellers, 

often inhabiting wind-swept maritime coasts, and a strong basal 

sheath has been evolved to strengthen their foothold. In some genera the 

sheath contains gonidia; in others the tissue is wholly of hyphae in nearly 

a cortex. 

every case it is protected by 

In the upright fronds the structure is radiate: generally a rather loose 

strand of hyphae more or less parallel with the long axis of the plant forms 

a central medulla. The gonidia lie outside the medulla and just within the 

outer cortex. The latter, in a few genera, is fibrous, the parallel hyphae 

being very closely compacted; but in most members of the family the 

fastigiate type prevails, as in the allied family Dirinaceae. 

d. THALLUS OF CYCLOCARPINEAE. This is by far the largest and most 

varied series of Archilichens. It is derived, as regards the fungal constituent, 

from the Discomycetes, but in these fungi, the vegetative or mycelial body 

gives no aid to the classification which depends wholly on apothecial 

characters. In the symbiotic condition, on the contrary, the thallus becomes 

of extreme importance in the determination of families, genera and species. 

There has been within the series a great development both of apothecial 

and of thalline characters in parallel lines or phyla. 

A A. LECIDEALES. The type of fruit nearest to fungi in form and origin 

occurs in the Lecideales. It is an open disc developed from the fungal symbiont 

alone, the alga taking no part. There are several phyla to be considered.


aa. COENOGONIACEAE. There are two types of gonidial algae in this 

family, and both are filamentous forms, Trentepohlia in Coenogonium and 

Cladophora in Racodium. The resulting lichens retain the slender thread-like 

form of the algae, their cells being thinly invested by the hyphae and both 

symbionts growing apically. The thalline filaments are generally very 

sparingly branched and grow radially side by side in a loose flat expansion 

attached at one side by a sheath, or the strands spread irregularly over the 

substratum. Plectenchyma appears in the apothecial margin in Coenogonium. 

Fruiting bodies are unknown in Racodium. 

Coenogoniaceae are a group apart and of slight development, only the 

one kind of thallus appearing; the form is moulded on that of the gonidium, 

and is, as Reinke 1 

to receive the maximum of 

illumination and aeration. 

remarks, perfectly adapted 

bb. LECIDEACEAE AND GYROPHORACEAE. The origin of this thalline phylum 

is distinct from that of the previous family, being associated with a different 

type of gonidium, the single-celled alga of the Protococcaceae. 

The. more elementary species are of extremely simple structure as 

exemplified in such species as Lecidea (Biatora) uliginosa or Lecidea granu- 

losa. These lichens grow on humus-soil and the thallus consists of a spreading 

mycelium or hypothallus with more or less scattered thalline granules containing 

gonidia, but without any defined structure. The first advance takes 

place in the aggregation and consolidation of such thalline granules and 

the massing of the gonidia towards the light, thus substituting the heteromerous 

for the homoiomerous arrangement of the tissues. The various 

characters of thickness, areolation, colour, etc. of the thallus are constant and 

are expressed in specific diagnoses. Frequently an amorphous cortex of 

swollen hyphae provides a smooth upper surface and forms a protective 

covering for such long-lived species as Rhizocarpon geographicum, etc. 

The squamulose thallus is well represented in this phylum. The squamules 

vary in size and texture but are mostly rather thick and stiff. In 

Lecidea ostreata they rise from the substratum in serried rows forming a 

dense sward; in L. decipiens, also a British species, the squamules are still 

are thick and firm and the 

larger, and more horizontal in direction ; they 

upper cortex is a plectenchyma of cells with swollen walls. Solitary hyphae 

from the medulla pass downwards into the support. 

Changes in spore characters also arise in these different thalline series, 

as for instance in genera such as Biatorina and Buellia, the one with colour- 

less, the other with brown, two-celled spores. These variations, along with 

changes in the thallus, are of specific or generic importance following the 

significance accorded to the various characters. 

In one lichen of the series, the monotypic Brazilian genus Spltaerophoropsis 

1 Reinke 1895, p. no. 

192

292 

PHYLOGENY 

stereocauloides, the thallus is described by Wainio 1 as consisting of minute 

clavate stalks of interwoven thick-walled hyphae, with gelatinous algae, like 

Gloeocapsa, interspersed in groups, though with a tendency to congregate 

towards the outer surface. 

The highest development along this line of advance is to be found in the 

Gyrophoraceae, a family of lichens with a varied foliose character and dark 

lecideine apothecia. The thallus may be monophyllous and of fairly large 

a central stout hold- 

dimensions or polyphyllous; it is mostly anchored by 

fast and both surfaces are thickly corticate with a layer of plectenchyma; 

the under surface is mostly bare, but may be densely covered with rhizinalike 

strands of dark hyphae. They are all northern species and rock-dwellers 

exposed to severe extremes of illumination and temperature, but well 

protected by the thick cortex and the dark colouration common to them all. 

cc. CLADONIACEAE. This last phylum of Lecideales is the most interesting 

as it is the most complicated. It possesses a primary, generally sterile, 

thallus which is dorsiventral and crustaceous, squamulose or in some instances 

almost foliaceous, along with a secondary thallus of upright radiate 

structure and of very varied form, known as the podetium which bears at 

the summit the fertile organs. 

A double thallus has been suggested in the spreading base, containing 

gonidia, of some radiate lichens such as Roccella, but the upright portion 

of such lichens, though analogous, is not homologous with that of 

Cladoniaceae. 

The algal cells of the family belong to the Protococcaceae. Blue-green 

algae are associated in the cephalodia of Pilophorus and Stereocaulon. 

The primary thallus is a feature of all the members, though sometimes very 

slight and very short-lived, as in Stereocaulon or in the section Cladina of 

the genus Cladonia. Where the primary thallus is most largely developed, 

the secondary (the podetium) is less prominent. 

This secondary thallus originates in two different ways: (i) the primary 

in the new 

granule may grow upward, the whole of the tissues taking part 

development; or (2) the origin may be endogenous and proceed from the 

hyphae only of the gonidial zone: these push upwards in a compact fascicle, 

as in the apothecial development of Lecidea, but instead of spreading outward 

on reaching the surface, they continue to grow in a vertical direction and 

form the podetium. In origin this is an apothecial stalk, but generally it is 

clothed with gonidial tissue. The gonidia may travel upwards from the 

base or they may possibly be wind borne from the open. The podetium 

thus takes on an assimilative function and is a secondary thallus. 

The same type of apothecium is common to all the genera ; the spores 

1 Wainio 1890.


are colourless and mostly simple, but there are also changes in form and 

septation not commensurate with thalline advance, as has been already noted. 

Thus in Gomphillus, with primitive thallus and podetium, the spores are 

long and narrow with about 100 divisions. 

1. ORIGIN OF CLADONIA. There is no difficulty in deriving Cladoniaceae 

from Lecidea, or, more exactly, from some crustaceous species of the section 

Biatora in which the apothecia as in Cladoniaceae are waxy and more 

or less light-coloured and without a thalline margin. In only a very few 

isolated instances has a thalline margin grown round the Cladonia fruit. 

There are ten genera included in the Cladoniaceae, of which five are 

British. Considerable study has been devoted to the elucidation of developmental 

problems within the family by various workers, more especially in the 

large and varied genus Cladonia which is complicated by the presence of 

the two thalli. The family is monophyletic in origin, though many subordi- 

nate phyla appear later. 

2. EVOLUTION OF THE PRIMARY THALLUS. At the base of the series we 

find here also an elementary granular thallus which appears in some species 

of most of the genera. In Gomphillus, a monospecific British genus, the 

granules have coalesced into a continuous mucilaginous membrane. In 

Baeomyces, though mostly crustaceous, there is an advance to the squamulose 

type in B. placophyllus, and in two Brazilian species described by Wainio, 

one of which, owing to the form of the fronds, has been placed in a separate 

genus Hcteromyces. The primary thallus becomes almost foliose also in 

Gymnoderma coccocarpum from the Himalayas, with dorsiventral stratose 

arrangement of the tissues, but without rhizinae. The greatest diversity 

is however to be found in Cladonia where granular, squamulose and almost 

foliose thalli occur. The various tissue formations have already been 

described 1 . 

3. EVOLUTION OF THE SECONDARY THALLUS. Most of the interest 

centres round the development and function of the podetium. 

In several 

genera the primordium is homologous with that of an apothecium its 

; 

elongation to an apothecial stalk is associated with delayed fructification, 

and it though has taken on the function of the vegetative thallus, the purpose 

of elongation has doubtless been to secure good light conditions for the 

fruit, and to facilitate a wide distribution of spores : therefore, not only in 

development but in function, its chief importance though now assimilative 

was originally reproductive. The vegetative development of the podetium is 

correlated with the reduction of the primary thallus which in many species 

bears little relation in size or persistence to the structure produced from it, 

as, for instance, in Cladonia rangiferina where the ground thallus is of the 

1 See Chap. III.

294 

PHYLOGENY 

scantiest and very soon disappears, while the podetial thallus continues to 

grow indefinitely and to considerable size. 

4. COURSE OF PODETIAL DEVELOPMENT. In Baeomyces the podetial 

primordium is wholly endogenous in some species, but in others the 

outer cortical layer of the primary thallus as well as the gonidial hyphae 

take part in the formation of the new structure which, in that case, is simply 

a vertical extension of the primary granule. This type of podetium called 

by Wainio 1 a pseudopodetium also recurs in Pilophorus and in Stereocanlon. 

To emphasize the distinction of origin it has been proposed to classify these 

two latter genera in a separate family, but in that case it would be necessary 

to break up the genus Baeomyces. We may assume that the endogenous 

origin of the "apothecial stalk" is the more primitive, as it occurs in the 

most primitive lecideine lichens, whereas a vertical thallus is always an 

advanced stage of vegetative development. 

Podetia are essentially secondary structures, and they are associated 

both with crustaceous and squamulose primary thalli. If monophyletic in 

origin their development must have taken place while the primary thallus 

was still in the crustaceous stage, and the inherited tendency to form podetia 

must then have persisted through the change to the squamulose type. In 

species such as Cl. caespiticia the presence of rudimentary podetia along 

with large squamules suggests a polyphyletic origin, but Wainio's 1 

opinion is 

that such instances may show retrogression from an advanced podetial form, 

and that the evidence inclines to the monophyletic view of their origin. 

The hollow centre of the podetium arises in the course of development 

and is common to nearly all advanced stages of growth. There are however 

some exceptions : in Glossodium aversum, a soil lichen from New 

Granada, and the only representative of the genus, a simple or rarely forked 

stalk about 2 cm. in height rises from a granular or minutely squamulose 

thallus. The apothecium occupies one side of the flattened and somewhat 

wider apex. There is no external cortex and the central tissue is of loose 

hyphae. In Thysanothecium Hookeri, also a monotypic genus from Australia, 

the podetia are about the same height, but, though round at the base, they 

broaden upwards into a leaf-like expansion. The central tissue below is of 

loose hyphae, but compact strands occur above, where the apothecium 

spreads over the upper side. The under surface is sterile and is traversed 

by nerve-like strands of hyphae. 

5. VARIATION IN CLADONIA. It is in this genus that most variation is to 

be found. Characters of importance and persistence have arisen by which 

secondary phyla may be traced within the genus: these are mainly (i) the 

relative development of the horizontal and vertical structures, (2) formation 

1 Wainio 1897.


of the scyphus and branching of the podetium, with (3) differences in colour 

both in the vegetative thallus and in the apothecia. 

Wainio has indicated the course of evolution on the following lines : 

(i) the crustaceous thallus is monophyletic in origin and here as elsewhere 

precedes the squamulose. The latter he considers to be also monophyletic, 

though at more than one point the more advanced and larger foliose forms 

have appeared : (2) the primitive podetium was subulate and unbranched, 

and the apex was occupied by the apothecium. Both scyphus and branching 

are later developments indicating progress. They are in both cases associated 

with fruit-formation scyphi generally arising from abortive apothecia 1 

branching from aggregate apothecia. In forms such as Cl. fimbriata, where 

both scyphiferous and subulate sterile podetia are frequent, the latter (sub- 

species fibula) are retrogressive, and reproduce the ancestral pointed podetium. 

(3) In subgen. Cenomyce, with a squamulose primary thallus, there is 

a sharp division into two main phyla characterized by the colour of the 

apothecia, brown in Ochrophaeae the colour being due to a pigment and 

red in Cocciferae where the colouring substance is a lichen-acid, rhodocladonic 

acid. In the brown-fruited Ochrophaeae there are again several secondary 

phyla. Two of these are distinguished primarily by the character of the 

the Chasmariae in which two or several branches arise from 

branching : (a) 

the same level, entailing perforation of the axils (Cl. furcata, Cl. rangiformis, 

Cl. squamosa, etc.), the scyphi also are perforated. They are further 

characterized by peltate aggregate apothecia, this grouping of the apothecia 

according to Wainio being the primary cause of the complex branching, 

the several fruit stalks growing out as branches. The second group (&), the 

Clausae, are not perforated and the apothecia are simple and broad-based 

on the edge of the scyphus (Cl. pyxidata, Cl. fimbriata, etc.), or on the tips 

of the podetia (Cl. cariosa, Cl. leptophylla, etc.). A third very small group 

also of Clausae called (c} Foliosae has very large primary squamules and 

reduced podetia (Cl. foliacea, etc.), while finally (d) the Ochroleucae, none of 

which is British, have poorly developed squamules and variously formed 

yellowish podetia with pale-coloured apothecia. 

The Cocciferae represent a phylum parallel in development with the 

Ochrophaeae. The species have perhaps most affinity with the Clausae, the 

vegetative thallus both the squamules and the podetia being very much 

alike in several species. Wainio distinguishes two groups based on a differ- 

ence of colour in the squamules, glaucous green in one case, yellowish in 

the other. 

6. CAUSES OF VARIATION. External causes of variation in Cladonia are 

chiefly humidity and light, excess or lack of either effecting changes which 

may have become fixed and hereditary. Minor changes directly traceable 

1 See Chap. III. 

,

296 

PHYLOGENY 

to these influences are also frequent, viz. size of podetia, proliferation and the 

production more or less of soredia or of squamules on the podetia, though 

only in connection with species in which these variations are already an 

acquired character. The squamules on the podetium more or less repeat 

the form of the basal squamules. 

/. PODETIAL DEVELOPMENT AND SPORE-DISSEMINATION. In a recent 

paper by Hans Sattler 1 the problem of podetial development in Cladonia 

is viewed from a different standpoint. He holds that as the podetia are 

apothecial stalks, their service to the plant consists in the raising of the 

mature fruit in order to secure a wide distribution of the spores, and that 

changes in the form of the podetium are therefore but new adaptations for 

the more efficient discharge of this function. 

Following out this idea he regards as the more primitive forms those in 

which both the spermogonia, as male reproductive bodies, and the carpogonia 

occur on the primary thallus, ascogonia and trichogynes being formed before 

the podetium emerges from the thallus. Fertilization thus must take place 

at a very early period, though the ultimate fruiting stage may be long 

delayed. Sattler considers that any doubt as to actual fertilization is without 

bearing on the question, as sexuality he holds must have originally existed 

and must have directed the course of evolution in the reproductive bodies. 

In this primitive group, called by him the "Floerkeana" group, the podetia 

are always short and simple, they are terminated by the apothecium and 

no scyphi are formed (Cl. Floerkeana, Cl. leptophylla, Cl. cariosa, Cl. caespi- 

ticia, Cl. papillaria, etc.). 

In his second or "pyxidata" group, he places those species in which the 

apothecia are borne at the edge of a scyphus. That structure he follows 

Wainio in regarding as a morphological reaction on the failure of the first 

formed apical apothecium: it is, he adds, a new thallus in the form of a 

spreading cup and bears, as did the primary thallus, both the female primordia 

and the spermogonia. In some species, such as Cl. foliacea, there may be 

either scyphous or ascyphous podetia, and spermogonia normally accompany 

the carpogonium appearing accordingly along with it either on the squamule 

or on the scyphus. 

As the pointed podetia are the more primitive, Sattler points out that 

they may reappear as retrogressive structures, and have so appeared in the 

"pyxidata" group in such species as Cl. fimbriata. He refers to Wainio's 

statement that the abortion of the apothecium being a retrogressive anomaly, 

while scyphus formation is an evolutionary advance, the scyphiferous species 

present the singular case, "that a progressive transmutation induced by 

a retrogressive anomaly has become constant." 

1 Sattler 1914.


His third group includes those forms that grow in crowded tufts or 

swards such as Cl. rangiferina, Cl.furcata, Cl. gracilis, etc. They originate, 

as did the pyxidata group, in some Floerkeana-\\\i& form, but in the "rangiferina" 

group instead.of cup-formation there is extensive branching. In the 

closely packed phalanx of branches water is retained as in similar growths 

of mosses, and moist conditions necessary for fertilization are thus secured 

as efficiently as by the water-holding scyphus. 

Sattler in his argument has passed over many important points. Above 

all he ignores the fact that whatever may have been the original nature 

and function of the podetium, it has now become a thalline structure and 

provides for the vegetative life of the plant, and that it is in its thalline 

condition that the many variations have been formed ; the scyphus is not, 

as he contends, a new thallus, it is only 

already acquired. 

an extension of thalline characters 

8. PILOPHORUS, STEREOCAULON AND ARGOPSIS. These closely related 

share with it the twofold thallus 

genera are classified with Cladonia as they 

and the lecideine apothecia. The origin of the podetium being different 

they may be held to constitute a phylum apart, which has however taken 

origin also from some Biatora form. 

The primary thallus is crustaceous or minutely squamulose and the 

podetia of Pilophorus, which are short and unbranched (or very sparingly 

branched), are beset with thalline granules. The podetia of Stereocaulon 

and Argopsis are copiously branched and are more or less thickly covered 

with minute variously divided leaflets. Cephalodia containing blue-green 

algae occur on the podetia of these latter genera; in Pilophorus they are 

intermixed with the primary thallus. 

The tissue systems are less advanced in these genera than in Cladonia : 

there, is no cortex present either in Pilophorus or in Argopsis or in some 

species of Stereocaulon, though in others a gelatinous amorphous layer 

covers the podetia and also the stalk leaflets. The stalks are filled with 

loose hyphae in the centre. 

BB. LECANORALES. This second group of Cyclocarpineae is distinguished 

by the marginate apothecium, a thalline layer providing a protecting amphithecium. 

The lecanorine apothecium is of a more or less soft and waxy 

consistency, and though the disc is sometimes almost black, neither hypothecium 

nor parathecium is carbonaceous as in Lecidea. The affinity of 

must have been from a 

Lecanora is with sect. Biatora, and development 

biatorine form with a persistent thallus. The margin or amphithecium 

varies in thickness: in some it is species but scanty and soon excluded by 

the over-topping growth of the disc, so that a zone of gonidia underlying 

the hypothecium is often the only evidence of gonidial 

fully formed fruits. 

intrusion left in

298 

PHYLOGENY 

The marginate apothecium has appeared once and again as we have 

seen. It is probable however that its first development was in this group of 

lichens, and even here there may have been more than one origin as there 

is certainly more than one phylum. 

aa. COURSE OF DEVELOPMENT. At the base of the series, the thallus is 

of the crustaceous type somewhat similar to that of Lecidea, but there are 

none of the very simple primitive forms. Lecanora must have originated 

when the crustaceous lecideine thallus was already well established. Its 

affinity is with Lecidea and not with any fungus: where the thallus is 

evanescent or scanty, its lack is due to retrogressive rather than to primitive 

characters. 

bb. LECANORACEAE.. A number of genera have arisen in this large family, 

but they are distinguished mainly if not entirely by spore characters, and 

by some systematists have all been included in the one genus Lecanora, 

since the changes have taken place within the developing apothecium. 

There is one genus, Harpidium, which is based on thalline characters,, 

represented by one species, H. rutilans, common enough on the Continent, 

but not yet found in our country. It has a thin crustaceous homoiomerous 

thallus, the component hyphae of which are divided into short cells closely 

packed together and forming a kind of cellular tissue in which the algae are 

interspersed. The dorsiventral stratose arrangement prevails however in the 

other genera and a more or less amorphous " 

decomposed " cortex is frequently 

present. The medulla rests on the substratum. 

With the stouter thallus, there is slightly more variety of crustaceous 

form than in Lecideaceae: there occurs occasionally an outgrowth of the 

thalline granules as in Haematomma ventosum which marks the beginning 

of fruticulose structure. Of a more advanced structure is the thallus of 

Lecanora esculenta, a desert lichen which becomes detached and erratic, and 

which in some of its forms is almost coralline, owing to the apical growth of 

the original granules or branches: a more or less radiate arrangement of 

the tissues is thus acquired. 

The squamulose type is well represented in Lecanora, and the species 

with that form of thallus have frequently been placed in a separate genus, 

Squamaria. These squamules are never very large; they possess an upper, 

somewhat amorphous, cortex; the medulla rests on the substratum, except 

in such a species as Lecanora lentigera, where they are free, a sort of fibrous 

cortex being formed of hyphae which grow in a direction parallel with the 

surface. In none of them are rhizinae developed. 

cc. PARMELIACEAE. The chief advance, apart from size, of the squamulose 

to the foliose type is the acquirement of a lower cortex along with definite 

organs of attachment which in Parmeliaceae are invariably rhizoidal and


are composed of compact strands of hyphae extending from the cells of 

the lower cortex. 

In the genus Parmelia rhizinae are almost a constant character, though 

in a few species, such as Parmelia physodes, they are scanty or practically 

absent. It is not possible, however, to consider that these species form a 

lower group, as in other respects they are highly evolved, and rhizinae may 

be found at points on the lower surface where there is irritation by friction. 

Soredia and isidia occur frequently and, in several species, almost entirely 

replace reproduction by spores. In one or two northern or Alpine species, 

P. stygia and P.pubescens, the lobes are linear or almost filamentous. They 

are retained in Parmelia because the apothecia are superficial on the fronds 

which are partly dorsiventral, and because rhizinae have occasionally been 

found. Some of the Parmeliae attain to a considerable size ; growth 

is centrifugal 

and long continued. 

Two monotypic genera classified under Parmeliaceae, Physcidia and 

Heterodea, are of considerable interest as they indicate the bases of parallel 

development in Parmelia and Cetraria. The former, a small lichen, is corticate 

only on the upper surface, and without rhizinae; and from the description, 

the cortex is of a fastigiate character. The solitary species grows on bark 

in Cuba; it is related to Parmelia, as the apothecia are superficial on the 

lobes. The second, Heterodea Mulleri, a soil-lichen from Australasia, is more 

akin to Cetraria in that the apothecia are terminal. The upper surface is 

corticate with marginal cilia, the lower surface naked or only protected by 

a weft of brownish hyphae amongst which cyphellae are formed ; pseudo- 

cyphellae appear in Cetraria. 

The genus Cetraria contains very highly developed thalline forms, either 

horizontal (subgenus Platysma), or upright (Eiicetraria}. Rhizinae are scanty 

or absent, but marginal cilia in some upright species act as haptera. Cetraria 

aculeata is truly fruticose with a radiate structure. 

An extraordinary development of the under cortex characterizes the 

genera Anzia 1 and Pannoparmelia: rhizinae-like strands formed from the 

cortical cells branch and anastomose with others till a wide mesh of a 

spongy nature is formed. They are mostly tropical or subtropical or Australasian, 

and possibly the spongy mass may be of service in retaining moisture. 

A species of Anzia has been recorded by Darbishire 2 from Tierra del Fuego. 

dd. USNEACEAE. As we have seen, the change to fruticose structure 

has arisen as an ultimate development in a number of groups; 

however its highest and most varied form in this family. Not only are there 

it reaches 

strap-shaped thalli, but a new form, the filamentous and pendulous, appears; 

it attains to a great length, and is fitted to withstand severe strain. The 

1 See p. 90. 

* Darbishire 1912.

3oo 

PHYLOGENY 

various adaptations of structure in these two types of thallus have already 

been described 1 . 

In Parmelia itself there are indications of this line of development in 

P. stygia, with short stiff upright branching fronds, and in P. pubescens, 

with its tufts of filaments, but these two species are more or less dorsiventral 

in structure and do not rise from the substratum. In Cetraria also there 

is a tendency towards upright growth and in C. aculeata even to radiate 

structure. But advance in these directions has stopped short, the true line 

of evolution passing through species like Parmelia physodes with raised, and 

in some varieties, tubular fronds, and the somewhat similar species P. Kamt- 

schadalis with straggling strap-like lobes, to Evernia. That genus is a true 

link between foliose and fruticose forms and has been classified now with 

one series, now with the other. 

In Evernia furfuracea, the lobes are free from the substratum except 

when friction causes the development of a hold-fast and the branching out 

of new lobes from that point. It is however dorsiventral in structure, the 

under surface is black and the gonidial zone lies under the upper cortex. 

Evernia prunastri is white below and is more fruticose in habit, the long 

fronds all rising from one base. They are thin and limp, no strengthening 

tissue has been evolved, and they tend to lie over on one side; both surfaces 

are corticate and gonidia sometimes travel round the edge, becoming fre- 

quently lodged here and there along the under side. 

The extreme of strap-shaped fruticose development 

genus Ramalina. In less advanced species 

is reached in the 

such as R. evernioides there is a 

thin flat expansion anchored to the substratum at one point and alike on 

both surfaces. In R.fraxinea the fronds may reach considerable width (var. 

ampliata), but in that and in most species there is a provision of sclerotic 

strands to support and strengthen the fronds. One of those best fitted to 

resist bending strains is R. scopulorum (siliquosd) which grows by preference 

on sea-cliffs and safely withstands the maximum of exposure to wind or 

weather. 

The filamentous structure appears abruptly, unless we consider it as 

foreshadowed by Parmelia pubescens. The base is secured by strong sheaths 

of enduring character; tensile strains are provided for either by a chondroid 

axis, as in Usnea, or by cortical development, as in Alectoria; the former 

method of securing strength seems to be the most advantageous to the plant 

as a whole, since it leaves the outer structures more free to develop, and there 

is therefore in Usnea a greater variety of branching and greater growth in 

length, which are less possible with the thickened cortex of Alectoria. 

ee. PHYSCIACEAE. There remains still an important phylum of Lecano- 

rales well defined by the polarilocular spores 2 . It also arises from a Biatora 

1 See p. 101. 2 See p. 188.


species and forms a parallel development. Even in this phylum there are two 

series : one with colourless spores and mostly yellow or reddish either in 

thallus or apothecium, and the other with brown spores and with cinereous- 

grey or brown thalli. The dark spores are in many of the species typically 

polarilocular, though in some the median septum is riot very wide and no 

canal is visible. Practically all of the lighter coloured forms contain parietin 

either in thallus or apothecia or in both ; it is absent in the dark-spored series. 

Among the lighter coloured forms it is difficult to decide which of these 

two striking characteristics developed first, the acid or the peculiar spore. 

Probably the acid has the priority: there is one common rock lichen in this 

country, Placodium rupestre (Lecanora irrubata\ which gives a strong red 

acid reaction with potash, but in which the spores are still simple, and the 

'fruit structure in the biatorine stage. Another species, PI. luteoalbum, with a 

purplish reaction in the fruit only, shows septate spores but with only a 

rather narrow septum. The development continues through biatorine forms 

to lecanorine with a fully formed thalline margin. Among these latter we 

encounter PI. nivale which is well provided with acid but in which the spores 

have become long and fusiform with little trace of the polar cells or central 

canal. We must allow here also for reversions, and wanderings from the 

straight road. 

From crustaceous the advance is normal and simple to squamulose forms 

which in this phylum maintain a stiff regularity of thalline outline termed 

"effigurate"; the squamules, developing from the centre, extend outwards in a 

radiate-stellate manner. There are also foliose thalli in the genus Xanthoria 

and fruticose in Teloschistes. The cortex in the former horizontal genus is of 

plectenchyma, and no peculiar structures have emerged. 

In Teloschistes the 

cortex is of compact parallel hyphae (fibrous) which form the strengthening 

structure of the narrow compressed fronds (T.flavicans}. 

In the brown-spored series there is a considerable number of species that 

are crustaceous united in the genus Rinodina, all of which have marginate 

apothecia. One of them, Rinodina oreina, approaches in thalline structure the 

effigurate forms of Placodium; while in R. isidioides, a rare British species, 

there is an isidioid squamulose development. 

Among foliose genera, the tropical genus Pyxine is peculiar in its almost 

lecideine fruit, a few gonidia occurring only in the early stages; its affinity 

with Physcia holds, however, through the one-septate brown spores with very 

thick walls and the reduced lumen of the cells. The more simple type of 

fruit may be merely retrogressive. 

Pliyscia, the remaining genus, is mainly foliose and with dorsiventral 

thallus. A few species have straggling semi-upright fronds and these have 

sometimes been placed in a separate genus Anaptychia. Only one " 

Anap- 

tychia" Ph. intricata, has a radiate structure with fibrous cortex all round ; 

in the others the upper cortex alone is fibrous of long parallel hyphae

302 PHYLOGENY 

but that character appears in nearly every one of the horizontal species as 

well, sometimes in the upper, sometimes in the lower cortex. 

In Physcia the horizontal thallus is of smaller dimensions than in Parmelia, 

and never becomes so free from the substratum: it is attached by 

rhizinae and soredia appear frequently. Very often the circular effigurate 

type of development prevails. 

It is difficult to trace with any certainty the origin of this series of the 

phylum. Some workers have associated it with the purely lecideine genus, 

Buellia, but the brown septate spores of the latter are of simple structure, 

though occasionally approaching the Rinodina type. There are also 

differences in the thallus, that of Buellia, especially when it is saxicolous, 

inclining to Rhizocarpon in form. It is more consistent with the outer and 

inner structure to derive Rinodina from some crustaceous Placodium form 

with a marginate apothecium, therefore from a form of fairly advanced 

development. As the parietin content disappeared perhaps from the preponderance 

of other acids the colouration changed and the spores became 

dark-coloured. 

Many genera and even families, such as Thelotremaceae, etc., have 

necessarily been omitted from this survey of phylogeny in lichens, but the 

tracing of the main lines of development has indicated the course of evolution, 

and has demonstrated not only the close affinity between the members 

of this polyphyletic class of plants, as shown in the constantly recurring 

thalline types, but it has proved the extraordinary vigour gained by both 

the component organisms through the symbiotic association. 

The principal phyla 1 

, developing on somewhat parallel lines, are given in 

the appended table : 

ARCHILICHENS 

1 Dr Church (1920) has published a new conception of the origin of lichens. See postscript at 

the end of the volume, p. 421.


SCHEME OF SUGGESTED PROGRESSION IN LICHEN STRUCTURE 

PYRENOCARPINEAE CONIOCARPINEAE 

PYRENOCARPEAE CONIOCARPEAE 

CYCLOCARPINEAE 

PHYCOLICHENS (CYANOPHILI) 

LECIDEALES LECANORALES POLARILOCULARES 

Usneae 

Stereocaulon Eucetraria Ramalina 

Ochropheae Cocciferae 

Evernia Teloschistes 

Gyrophoraceae Cladbnia Pilophoro 

Psora 

{Sect. Sect. Eulecidea 

Lecidea 

(Protococcaceae) 

Cetraria Parmelia 

(Platysma) physodes 

Parme- 

Xantnoria 

Heterodea Physcidia lEuplacodium 

Physcia 

sect. 

Anaptychia 

Physcia 

êcanora sect. -I 

\ ICallopisma 

Squamaria JPlacodium \ Rinod 

I 

IBUstenU i 

| | 

Lecanora Colourless spores 

Sect. Biatora 

I

CHAPTER VIII 

SYSTEMATIC 

I. CLASSIFICATION 

A. WORK OF SUCCESSIVE SYSTEMATISTS 

SINCE the time when lichens were first recognized as a separate class 

as members of the genus Lichen by Tournefort 1 or as "Musco-fungi" 

by 

Morison 2 

, many 

schemes of classification have been outlined, and the 

history of the science of lichenology, as we have seen, is a record of attempts 

to understand their puzzling structure, and to express that understanding 

by relating them to each other and to allied classes of plants. The great 

diversity of opinion in regard to their affinities is directly due to their 

composite nature. 

a. DILLENIUS AND LINNAEUS. The first systematists were chiefly im- 

pressed by their likeness to mosses, hepatics or algae. Dillenius* in the 

Historia Muscorum grouped them under the moss genera: IV. Usnea, 

V. Coralloides and VI. Lichenoides. Linnaeus 4 classified them among algae 

under the general name Lichen, dividing them into eight orders based on 

thalline characters in all but one instance, the second order being distin- 

guished from the first by bearing scutellae. The British botanists of the 

latter part of the eighteenth century Hudson, Lightfoot and others were 

content to follow Linnaeus and in general adopted his arrangement. 

b. ACHARIUS. Early in the nineteenth century Acharius, the Swedish 

Lichenologist, worked a revolution in the classification of lichens. He gave 

first place to the form of the thallus, but he also noted the fundamental 

differences in fruit-formation: his new system appeared in the Methodus 

Lichenum 5 with an introduction explaining the terms he had introduced, 

many of them in use to this day. 

Diagnoses of twenty-three genera are given with their included species. 

The work was further extended and emended in Lichenographia Uni- 

versalis* and in the Synopsis Lichenum 1 . In his final arrangement the 

family "Lichenes" is divided into four classes, three of which are characterized 

solely by apothecial characters; the fourth class has no apothecia. 

They 

are as follows : 

Class I. Idiothalami with three orders, Homogenei, Heterogenei and Hyperogenei : 

the apothecia differ in texture and colouration from the thallus: Lecidea, Opegrapha, 

Gyrophora, etc. 

Class II. Coenothalami, with three orders, Phymaloidei, Discoidei and Cephaloidei. 

1 

Tournefort 1694. 

2 Morison 1699. 

3 Dillenius 1741. 

4 

Linnaeus 1753. 



7 Acharius 1814.

FAMILIES AND GENERA 305 

The apothecia are partly formed from the thallus: Lecanora, Parme/ta, etc. The 

Pyrenolichens are also included by him in this class, because "the thallus surrounds and 

is concrete with the partly or wholly immersed apothecia." 

Class III. Homothalami with two orders, Scutellati and Peltati. The apothecia are 

formed from the cortical and medullary tissue of the thallus : Ramalina, Usnea, Collema, 

etc. 

Class IV. Athalami, with but one sterile genus, Lepraria. 

The orders are thus based on the form of the fruit; the genera in the 

Synopsis number 41. Large genera such as Lecanora with 132 species are 

divided into sections, many of which have in turn been established as 

genera, by S. F. Gray in 1821, and later by other systematists. 

The Synopsis was the text-book adopted by succeeding botanists for 

some 40 years with slight alterations in the arrangement of classes, genera, 

etc. 

Wallroth 1 and Meyer 2 followed with their studies on the lichen thallus, 

and Wallroth's division into "Homoiomerous" and "Heteromerous" was 

accepted as a useful guide in the maze of forms, representing 

a great natural distinction. 

as it did 

c. SCHAERER. This valiant lichenologist worked continuously during 

the first half of the nineteenth century, but with very partial use of the 

microscope. His last publication in 1850, an Enumeration of Swiss Lichens, 

was the final declaration of the older school that relied on field characters. 

His classification is as follows : 

Class I. Lichenes Discoidei, with ten orders from Usneacei to Graphidei fruits 

; 

open. 

Class II. Lichenes Capitati, with three orders: Calicioidei, Sphaerophorei and Cla- 

doniacei ; 

fruits stalked. 

Class III. Lichenes Verrucarioidei, with three orders: Verrucarii, Pertusarii and 

Endocarpei 

: fruits closed. 

An "Appendix" contains descriptions of Crustacei and Fruticulosi, all 

sterile forms, except Coniocarpon and Arthonia, which seem out of place, 

and finally a "Corollarium" of gelatinous lichens all classified under one 

genus Collema. 

d. MASSALONGO AND KOERBER. As a result of their microscopic 

studies, these two workers proposed many changes based on fruit and 

spore characters, and Koerber in the Systema Lichenum Germaniae (1855) 

gave expression to these views in his classification. He also made use of 

Wallroth's distinctions of "homoiomerous" and "heteromerous," thus dividing 

lichens at the outset into those mostly with blue-green and those with bright- 

green gonidia. 

1 Wallroth 1825. 

* Meyer ' 82 5-

3o6 SYSTEMATIC 

The following is the main outline of Koerber's classification: 

Series I. Lichenes Heteromerici. 

Order I. Lich. Thamnoblasti (fruticose). 

Order II. Lich. Phylloblasti (foliose). 

Order III. Lich. Kryoblasti (crustaceous). 

Series II. Lichenes Homoeomerici. 

Order IV. Lich. Gelatinosi. 

Order V. Lich. Byssacei. 

With the exception of Order V all are subdivided into two sections, 

"gymnocarpi" with open fruits and "angiocarpi" with closed fruits, a 

distinction that had long been recognized both in lichens and in fungi. 

e. NYLANDER. The above writers had been concerned with the inter- 

relationships of lichens ; Nylander, who was now coming forward as a 

lichenologist of note, gave a new turn to the study by dwelling on their 

relation to other classes of plants. Without for a moment conceding that 

they were either algal or fungal, he yet insisted on their remarkable affinity 

to algae on the one hand, and to fungi on the other, and he sought to make 

evident this double connection by his very ingenious scheme of classfication 1 . 

He began with what we may call "algal lichens," those associated with 

blue-green gonidia in the family "Collemacei"; he continued the series to 

the most highly evolved foliose forms and then wound up with those that 

are most akin to fungi, that is, those with least apparent thalline formation 

according to him the " Pyrenocarpei." 

In his scheme, which is the one followed by Leighton and Crombie, the 

"family" represents the highest division; series, tribe, genus and species 

come next in order. We have thus : 

Fam. I. Collemacei. 

Fam. II. Myriangiacei (now reckoned among fungi). 

Fam. III. Lichenacei. 

This last family, which includes the great bulk of lichens, is divided into 

the following series: I. Epiconiodei; II. Cladoniodei; III. Ramalodei ; 

IV. Phyllodei; V. Placodei; VI. Pyrenodei. It is an ascending series up 

to the Phyllodei, or foliaceous lichens, which he considers higher in development 

than the fruticose or filamentous Ramalodei. The Placodei include 

four tribes on a descending scale, the Lecanorei, Lecidinei, Xylographidei 

and Graphidei. The classification is almost wholly based on thalline form, 

except for the Pyrenodei in which are represented genera with closed fruits, 

there being one tribe only, the Pyrenocarpei. 

Nylander claims however to have had regard equally to the reproductive 

system and was the first to give importance to the spermogonia. The 

classification is coherent and easy to follow, though, like all classifications 

1 

Nylander 1854.


based on imperfect knowledge, it is not a little artificial ; 

also while magnifying 

the significance of spermogonia and spermatia, he overlooked the much 

more important characters of the ascospores. 

/. Mt)LLER(-ARGAU). In preparing his lists of Genevan lichens (1862), 

Miiller realized that Nylander's series was unnatural, and he found as he 

studied more deeply that lichens must be ranged in parallel or convergent 

but detached groups. He recognized three main groups : 

1. Eulichens, divided into Capitularieae, Discocarpeae and Verru- 

caroideae. 

2. Epiconiaceae. 

Collemaceae. 

3. 

He suggested that, in relation to other plants, Eulichens approach 

Pezizae, Hysteriaceae and Sphaeriaceae; Epiconiaceae have affinity with 

Lycoperdaceae, while Collemaceae are allied to the algal family Nostocaceae. 

These three groups of Eulichens, he held, advanced on somewhat 

parallel lines, but reached a very varied development, the Discocarpeae 

attaining the highest stage of thalline form. M tiller accepted as characters 

of generic importance the form and structure of the fruiting body, the 

presence or absence of paraphyses, and the septation, colour, etc. of the spores. 

A few years later (1867) the composite nature of the lichen thallus was 

announced by Schwendener, and, after some time, was acknowledged by 

most botanists to be in accordance with the facts of nature. Any system 

of classification, therefore, that claims to be a natural one, must, while 

following as far as possible the line of plant development, take into account 

the double origin of lichens both from algae and fungi, the essential unity 

and coherence of the class being however proved by the recurring similarity 

between the thalline types of the different phyla. As Muller had surmised: 

"they are a series of parallel detached though convergent groups." 

g. REINKE. The arrangement of Ascolichens on these lines was first 

seriously studied by 

1 Reinke and his , conclusions, which are embodied 2 in 

the Lichens of Schleswig-Holstein, have been largely accepted by succeeding 

workers. He recognizes three great subclasses: I. Coniocarpi; 2. Disco- 

carpi; 3. Pyrenocarpi. 

The Coniocarpi are a group apart, but as their fruit is at first entirely 

closed at least in some of the genera the more natural position for them 

is between Discocarpi and Pyrenocarpi. It is in the arrangement of the 

Discocarpi that variation occurs. Reinke's arrangement of orders and 

families in that subclass is as follows : 

Subclass 2. Discocarpi. 

Order I. GRAMMOPHORI: Fam. GRAPHIDACEI and XYLOGRAPHACEI. 

1 Reinke 1894, '95, '96. 

2 Darbishire and Fischer- Benzon 1901. 

20 2

3o8 

SYSTEMATIC 

Order II. LECIDEALES: Fam. GYALECTACEI, LECIDEACEI, UMBILICARI- 

ACEI and CLADONIACEI. 

Order III. PARMELIALES: Fam. URCEOLARIACEI, PERTUSARIACEI, PAR- 

MELIACEI, PHYSCIACEI, TELOSCHISTACEI and ACAROSPORACEI. 

Order IV. CYANOPHILI: Fam. LICHINACEI, EPHEBACEI, PANNARIACEI, 

Sr/CTACf, PELTIGERACEI, COLLEMACEI and OMPHALARIACEI. 

The orders represent generally the principal phyla or groups, the families 

subordinate parallel phyla within the orders. The first three orders are 

stages of advance as regards fruit development ; 

the Cyanophili are a group 

apart. 

Wainio 1 rendered great service to Phylogeny in his elaborate work on 

Cladoniaceae, the most complicated of all the lichen phyla. He also drew 

up a scheme of arrangement in his work on Brazil Lichens 2 . There is in 

it some divergence from Reinke's arrangement, as he tends to give more 

importance to the thallus than to fruit characters as a guide. He places, for 

instance, Gyrophorei beside Parmelei and at a long distance from his Lecidei. 

The Cyanophili group of families he has interpolated between Buelliae 

(Physciaceae) and Lecideae. Many workers approve of Wainio's classifica- 

tion but it presents some difficult problems. 

h, ZAHLBRUCKNER. The systematist of greatest weight in recent times 

is A. Zahlbruckner, who is responsible for the systematic account of lichens 

in Engler and Prantl's Naturlichen Pflanzenfamilien. It is difficult to 

express the very great service he has rendered to Lichenology, in that and 

other world-wide studies of lichens. The sketch of lichen phylogeny as 

given in the present volume owes a great deal to the sound and clear 

guidance of his work, though his conclusions may not always have been 

accepted. The classification in the Pflanzenfamilien is the one now generally 

followed. 

The class Lichenes is divided by Zahlbruckner 3 into two subclasses, 

I. Ascolichens and II. Hymenolichens. He gives a third class, Gastero- 

lichens 4 but as it was , founded on error 5 

, it need not concern us here. The 

Ascolichens are by far the more important. These are subdivided into: 

Series I. PYRENOCARPEAE, with perithecial fruits. 

Series 2. GYMNOCARPEAE, with apothecial fruits. 

These are again broken up into families, and in the arrangement and 

sequence of the families Zahlbruckner indicates his view of development 

and relationship. They occur in the following order: 

1 Wainio 1887, '94, '97. 

4 Massee 1887. 


5 Fischer 1890. 

3 Zahlbruckner 1907.


SERifcs i. PYRENOCARPEAE 

ALGAL CELLS PROTOCOCCACEAE OR PALMELLA. 

MORIOLACEAE \ 

EPIGLOEACEAE \, Thallus crustaceous, perithecia solitary 

VERRUCARIACEAE] 

DERMATOCARPACEAE. Thallus squamulose or foliose. 

P YRENO THAMNIA CEA E. Thallus fruticose. 

ALGAL CELLS PRASIOLA. 

VI. MASTOIDIACEAE. 

ALGAL CELLS TRENTEPOHLIA. 

VII. PYRENULACEAE } 

VIII. PARATHELIACEAEY Thallus crustaceou s, perithecia occurring singly. 

IX. TRYPE^HELIACEAE\ . 

X. ASTROTHELIACEAE}' Thallus crustaceous, perithecia united (stromatoid). 

J XI. MYCOPORACEAE. Thallus crustaceous, perithecia in compact groups with a 

common outer wall. 

XII. PHYLLOPYREN1ACEAE. Thallus minutely foliose. 

ALGAL CELLS PHYLLACTIDIUM OR MYCOIDEA. 

XIII. STRIGULACEAE. Tropical leaf-lichens. ,,*-. 

ALGAL CELLS NOSTOC OR SCYTONEMA. 

XIV. PYRENIDIACEAE. Thallus minutely squamulose or fruticose. 

SERIES 2. GYMNOCARPEAE 

Subseries i. Coniocarpineae, with subperithecial fruits. 

Subseries 2. Graphidineae, with elongate, narrow fruits. 

Subseries 3. Cyclocarpineae, with round open fruits. 

SUBSERIES i. CONIOCARPINEAE 

This is a well-defined group, peculiar in the disappearance of the asci at an early stage 

so that the spores lie like a powder in the globose partly closed fruits. Algal cells, bright- 

green ; Protococcaceae. There are only three families : 

XV. CALICIACEAE. Thallus crustaceous, apothecia stalked. 

XVI. CYPHELIACEAE. Thallus crustaceous, apothecia sessile. 

XVII. SPHAEROPHORACEAE. Thallus foliose or fruticose, apothecia sessile. 

SUBSERIES 2. GRAPHIDINEAE 

This subseries comes next in the form of fruit development ; generally the apothecia 

are elongate, with a narrow slit-like opening, so that a transverse section shows almost a 

perithecial outline. Algal cells are mostly Trentepohlia. 

XVII!. ARTHONIACEAE. Thallus crustaceous, apothecia oval or linear, flat. 

XIX. GRAPHIDACEAE. Thallus crustaceous, apothecia linear, raised. 

XX. CHIODECTONACEAE. Thallus crustaceous, apothecia generally immersed in 

a stroma. 

DIRINACEAE. Thallus crustaceous, corticate above, apothecia round. 

ROCCELLACEAE. Thallus fruticose, apothecia round or elongate. 


SUBSERIES 3. 

A large and very varied ! group In most of the families the algal cells are bright-green 

(Chlorophyceae), in some they are blue-green (Cyanophyceae), these latter corresponding 

to Reinke's order Cyanophili. The apothecia, as the name implies, are round and open ; 

the "Cyanophili" have been placed by Zahlbruckner after those families in which the

3io 

XXIII. 

XXIV. 

XXV. 

> XXVI. 

XXVII. 

XXVIII. 

SYSTEMATIC 

apothecium has no thalline margin. They form a phylum distinct from those that precede 

and those that follow. 

The first family of the Cyclocarpineae, the Lecanactidaceae, is often placed under 

Graph idineae; in any case it forms a link between the two subseries. 

XXX. 

XXXI. 

XXXII. 

XXXIII. 

XXXIV. 

XXXV. 

i. Lecideine group (apothecia without a thalline margin). 

LECANACTIDACEAE. Thallus crustaceous. Algal cells Trentepohlia. 

Apothecium with carbonaceous hypothecium or parathecium. 

PILOCARPACEAE. Thallus crustaceous. Algal cells Protococcaceae. Apothecia 

with a dense rather dark hypothecium. 

CHRYSOTHRICACEAE. Thallus felted, loose in texture. Algal cells Pal- 

mella^ Protococcaceae or Trentepohlia. Apothecia with or without a thalline 

margin. The affinity of the "Family" seems to be with Pilocarpaceae. 

\ 

THELOTREMACEAE [ 

DIPLOSCHISTAChAE( 

Thallus crustaceous. Algal cells in the first Trentepohlia; 

in the second Protococcaceae. In both 

there are prominent double margins round the 

' 

apothecium. 

ECTOLECHIACEAE. Thallus very primitive in type. Algal cells Proto- 

coccaceae. Apothecia with or without a thalline margin. Nearly related to 

Chrysothricaceae. 

GYALECTACEAE. Thallus crustaceous. Algal cells Trentepohlia, Phyllactidium 

or rarely Scytonema. Apothecia biatorine, i.e. of soft consistency and 

without gonidia. 

COENOGONIACEAE. Thallus confusedly filamentous (byssoid). Algal cells 

Trentepohlia or Cladophora. Apothecia biatorine. 

LECIDEACEAE. Thallus crustaceous or squamulose. Algal cells Proto- 

coccaceae. Apothecia biatorine (soft), or lecideine (carbonaceous). 

PHYLLOPSORACEAE. Thallus squamulose or foliose. Algal cells Protococcaceae. 

Apothecia biatorine or lecideine. 

CLADONIACEAE. Thallus twofold. Algal cells Protococcaceae. thecia biatorine or lecideine. 

Apo- 

GYROPHORACEAE. 

thecia lecideine. 

Thallus foliose. Algal cells Protococcaceae. Apo- 

ACAROSPORACEAE. Thallus primitive crustaceous, squamulose or foliose. 

Algal cells Protococcaceae. Apothecia with or without a thalline margin ; 

very various, but always with many-spored asci. 

2. Cyanophili group. 

In this group the classification depends almost entirely on the nature of the algal 

constituents. The apothecia are in most genera provided with a thalline margin. 

a. More or less gelatinous when moist. 

XXXVI. EPHEBACEAE. Algal cells Scytonema or Stigonema. Thallus fruticose or filamentous. 

minutely 

XXXVII. PYRENOPSIDACEAE. Algal cells Gloeocapsa (Gloeocapsa, Xanthocapsa 

XXXVIII. 

or Chroococcus}. Thallus crustaceous, minutely foliose or fruticose. 

LICHINACEAE. Algal cells Rivularia. Thallus crustaceous, squamulose 

XXXIX. 

or minutely fruticose. 

COLLEMACEAE. Algal cells Nostoc. Thallus crustaceous, minutely fruti- 

cose, or squamulose to foliose. 

XL. HEPPIACEAE. Algal cells Scytonema. Thallus generally squamulose 

and formed of plectenchyma.


b. Not gelatinous when moist. 

^~\ XLl. PANNARIACEAE. Algal cells Nostoc, Scytonema or rarely bright-green, 

' 

Protococcaceae. Thallus crustaceous, squamulose or foliose. 

XLll. STICTACEAE. Algal cells Nostoc or Protococcaceae. Thallus foliose, 

XLIII. 

and very highly developed, corticate on both surfaces. 

PELTIGERACEAE. Algal cells Nostoc or Protococcaceae. Thallus 

foliose, corticate above. 

3. Lecanorine group (apothecia with a thalline margin). 

The remaining families have all bright-green gonidia and nearly always apothecia 

with a thalline margin. The group includes several distinct phyla : 

XLIV. PERTUSARIACEAE. Thallus crustaceous. Apothecia, one or several 

immersed in thalline tubercles ; spores mostly very large. 

XLV. LECANORACEAE. Thallus crustaceous or squamulose. Apothecia mostly 

superficial. 

XLVI. PARMELIACEAE. Thallus foliose, rarely almost fruticose or filamentous. 

Apothecia scattered over the surface or marginal, sessile. 

XLVI I. USNEACEAE. Thallus fruticose or filamentous. Apothecia sessile or 

shortly stalked. 

N] XLVI 1 1. CALOPLACACEAE. Thallus crustaceous, squamulose or minutely fruti- 

cose. Apothecia with polarilocular colourless spores. 

XLIX. TELOSCHISTACEAE. Thallus foliose or fruticose. Apothecia with 

polarilocular colourless spores. 

L. BUELLIACEAE. Thallus crustaceous or squamulose. Apothecia (lecideine 

or lecanorine) with two-celled, thick-walled brown spores (polarilocular in 

part). 

LI. PHYSCIACEAE. Thallus foliose, rarely partly fruticose. Apothecia with 

two-celled thick-walled brown spores (polarilocular in part). 

Subclass 2. Hymenolichens. 

There are only three closely related genera of Hymenolichens, Cora, 

Corella and 

Dictyonema with Chroococcus or Scytonema algae. 

There is reason to dissent from the arrangement in one or two instances which will 

be pointed out in the following examination of families and genera. 

B. FAMILIES AND GENERA OF ASCOLICHENS 

The necessity for a well-reasoned and well-arranged system of classification 

is self-evident: without a working knowledge of the plants that are 

the subject of study no progress can be made. The recognition of plants 

as isolated individuals is not sufficient, it must be possible to place them in 

relation to others; hence the importance of a natural system. In identifying 

species artificial aids, such as habitat and substratum, are also often of great 

value, and a good working system should take account of all characteristics. 

Lichen development is the result of two organisms mutually affecting 

each other, but as the fungus provides the it is 

reproductive system, 

the 

dominant partner : the main lines of classification are necessarily determined

3 i2 

SYSTEMATIC 

by fruit characters. The algae occupy a subsidiary position, but they also 

are of importance in shaping the form and structure of the thallus. The 

different phyla are often determined by the presence of some particular alga ; 

it is in the delimitation of families that the algal influence is of most effect. 

Zahlbruckner's system gives due weight to the inheritance from both 

fungus and alga with, however, the fungus as the chief factor in development, 

and as his work is certain to be generally followed by modern lichenologists, 

it is the one of most immediate interest. His scheme has been accepted in 

the following more detailed account of families and genera, and for the 

benefit of home workers those that have not so far been recorded from the 

British Isles have been marked with an asterisk. 

It cannot be affirmed that nomenclature is as yet firmly established in 

lichenology. Both on historical grounds and on those of convenience, the 

subject is one of extreme importance, and interest in it is one of the main 

avenues by which we secure continuity with the past, and by which we are 

able to realize not only the difficulty, but the romance of pioneer work. 

Besides, there can be no exchange of opinion between students nor assured 

knowledge of plants, until the names given to them are beyond dispute. 

According to the ruling of the Brussels Botanical Congress in 1910, 

Linnaeus's 1 list of lichens in the Species Plantarum has been selected as the 

basis of nomenclature, but since his day many new families, genera and 

species have been described and often insufficiently delimited. It is not 

easy to decide between priority, which appeals to the historical sense, and 

recent use which is the plea of convenience. Here also it seems there can 

be no rigid decision; the one aim should be to arrive at a conclusion 

satisfactory to all, and accepted by all. 

In the following necessarily brief account of families and genera, the 

"spermogonia" or "pycnidia" have in most cases been left out of account, 

as in many instances they vary within the family and occasionally even 

within the genus. Their taxonomic value is not without importance, but, 

in the general systematic arrangement, they are only subsidiary characters. 

An account of them has already been given, and for more detailed statements 

the student is referred to purely systematic works. 

There are two main types of spore production in the "pycnidia" which 

have been shortly described by Steiner 2 as "exobasidial" and "endobasidial." 

In the former the sporophores are simple or branched filaments, at the 

apices of which a short process grows out and buds off a pycnidiospore; 

in the latter the spores are budded directly from cells lining the walls or* 

filling the cavity of the pycnidium. The exobasidial type is more simply 

rendered in the following pages by "acrogenous," the endobasidial by 

"pleurogenous" spore production. In many cases the "spermogonia" or 


2 Steiner 1901.


"pycnidia" are still imperfectly known. In designating the gonidial algae, 

the more comprehensive Protococcaceae has been substituted for Protococcus, 

as in many cases the alga is* probably not Protococcus as now understood, 

but some other genus of the family 1 . 

SUBCLASS I. ASCOLICHENS 

SERIES I. PYRENOCARPINEAE 

It is on mycological grounds that Pyrenocarpineae are placed at the 

base of lichen classification. There is no evidence that the series was first 

in time. 

I. MORIOLACEAE 

This family was described by Norman 2 in 1872 from specimens col- 

lected by himself in Norway or in the Tyrol, on soil or more frequently on 

trees. There seems to have been no further record, and Zahlbruckner, 

while accepting the family, suggests that an examination or revision may 

be necessary. 

The thallus is crustaceous. The algal cells, Protococcaceae, occur either 

in groups (sometimes stalked) surrounded by a plectenchymatous wall and 

called by Norman "goniocysts," or they form nests in the thallus termed 

"nuclei" which are surrounded by a double wall of plectenchyma, colourless 

in the interior and brown outside. Norman invented the term "Allelositis- 

mus," which ,may be rendered "mutualism," to indicate this peculiar form 

of thallus. The species of Spheconisca are fairly numerous on poplars, willows 

and conifers: 

; 

Algae in 'goniocysts" i. *Moriola Norm. 3 

Algae in double-walled "nuclei" ... 2. *Spheconisca Norm. 

II. EPIGLOEACEAE 

The family consists of but one genus and one species, Epigloea bactrospora, 

and, according to Zahlbruckner, further examination is necessary to make 

certain as to the lichenoid nature of the plant. 

Zukal 4 found the perithecia scattered over the leaves of mosses, and he 

alleges that hyphae connected with the perithecium were closely associated 

with the alga, Palmella botryoides, and were causing it no harm. Along with 

the perithecia he also found minute pycnidia. The "thallus" is of a gelatinous 

nature and homoiomerous in structure; the perithecia are soft and clear- 

coloured with many-spored asci and colourless one-septate spores. 

The small globose pycnidia contain simple sporophores and acrogenous 

straight or slightly bent rod-like spores. 

Asci many-spored ; spores one-septate, i. *Epigloea Zukal. 

1 2 See p. 56. 

Norman 1872 and '74. 

3 Genera marked with an asterisk have not been found in the British Isles. 

4 Zukal 1890.

3 i 4 

SYSTEMATIC 

III. VERR UCARIA CEA E 

In all the genera of this family the thallus is crustaceous, and, with very 

few exceptions, the species are saxicolous or terricolous. The thallus is 

variable within the crustaceous limits, and may be superficial and very 

conspicuous, almost imperceptible, or wholly immersed in the substratum. 

The algal cells are Protococcaceae, and in two of the genera the green cells 

penetrate the hymenium and grow in rows alongside of the asci. The 

perithecia are small roundish structures scattered over the thallus, the base 

immersed, but the upper portion generally projecting. An outer darkcoloured 

wall surrounds the whole perithecium (entire) or only the upper 

or ostiole more or 

exposed portion (dimidiate) ; it opens above by a pore 

less prominent. 

In some of the genera the paraphyses become dissolved at an early 

stage, and somewhat similar filaments near the ostiole, termed periphyses, 

aid in the expulsion of the spores. The spores vary in septation, colour 

and size, and these variations have served to delimit the genera which 

have been formed from the original very large genus Verrucaria. The ascus 

may be 1-2-, 4- or 8-spored. In only one genus is it many-spored 

( Trimmatothele). 

The genera are as follows : 

Perithecia with simple ostioles. 

Paraphyses disappearing early, or wanting. 

Spores simple, ellipsoid I. Verrucaria Web. 

Spores simple, elongate vermiform 2. Sarcopyrenia Nyl. 

Spores simple, numerous in the ascus 3. *Trimmatothele Norm. 

Spores i-3-septate 4. Thelidium Massal. 

Spores murifbrm (with transverse and longitudinal divisions). 

Without hymenial gonidia 5. Polyblastia Massal. 

With hymenial gonidia 6. Staurothele Norm. 

Paraphyses present. 

Spores simple. 

Without hymenial gonidia 7. Thrombium Wallr. 

With hymenial gonidia 8. *Thelenidia Nyl. 

Spores 3-septate, broadly ellipsoid 9. *Geisleria Nitschke. 

Spores acicular, many-septate 10. Gongylia Koerb. 

Spores muriform u. Microglaena Lonnr. 

Perithecia with a wide ring round the ostiole. 

Spores muriform; paraphyses unbranched 12. *Aspidothelium Wain. 

Spores elongate, many-septate; paraphyses branched 13. *Aspidopyrenium Wain. 

IV. DERMATOCARPACEAE 

In this family there is a much more advanced thalline development 

generally squamulose or with some degree of foliose structure, though in 

the genus Endocarpon, some of the species are little more than crustaceous.


The gonidia are bright-green Protococcaceae (according to Chodat, Cocco- 

botrys in Dermatocarpori). In Endocarpon they appear in the hymenium. 

in structure is Normandina the thallus of the 

The least developed : 

single species consists of delicate shell-like squamules which are noncorticate 

above and below. In the other genera there is a cortex of 

plectenchyma. 

The perithecia are almost wholly immersed, and open above by a straight 

ostiole. The fructification of Dacampia is considered by some lichenologists 

to be only a parasite on the white thickish squamulose thallus with which 

it is associated. 

Hymenial gonidia present. 

Spores muriforrn I. Endocarpon Hedw. 

Hymenial gonidia absent. 

Thallus non-corticate 2. Normandina Wain. 

Thallus corticate. 

Spores simple, colourless 3. Dermatocarpon Eschw. 

Spores simple, brown 4. *Anapyrenium Miill.-Arg. 

Spores elongate-septate, colourless 5. *Placidiopsis Beltr. 

Spores elongate-septate, brown 6. *Heterocarpon Miill.-Arg. 

Spores muriforrn, colourless 7. *Psoroglaena Miill.-Arg. 

Spores muriforrn, brown 8. Dacampia Massal. 

V. PYRENOTHAMNIACEAE 

Thallus more or less fruticose and corticate on both surfaces. Algal 

cells Protococcaceae. 

Only two genera are included in this family : Nylanderiella 

with one 

species from New Zealand, with a small laciniate thallus up to 15 mm. in 

height, partly upright, partly decumbent, and attached to the substratum by 

basal rhizinae the other small ; 

genus, Pyrenothamnia, belongs to N. America ; 

the thallus has a short rounded stalk which expands above to an irregular 

frond. The perithecia are immersed in the fronds. 

Spores colourless, i-septate i. *Nylanderiella Hue 1 . 

Spores brown, muriforrn 2. *Pyrenothamnia Tuckerm. 

VI. MASTOIDEACEAE 

A family containing one genus and one species, with a wide distribution, 

having been found in Siberia, on the Antarctic continent (Graham's Land), 

as also in Tierra del Fuego, South Georgia, South Shetland Islands and 

Kerguelen. The thallus is foliose, of small thin lobes, and without rhizinae. 

Algal cells Prasiola-. The perithecia are globose and partly project from 

the thallus; the asci are 8-spored; the paraphyses are mucilaginous and 

partly dissolving. 

Spores elongate-fusiform, simple, colourless ...i. *Mastoidea Hook, and Harv. 

1 Hue 1914. 

2 Hue 1909.

3 i6 

SYSTEMATIC 

VII. PYRENULACEAE 

This family of crustaceous lichens differs from Verrucariaceae chiefly in 

the gonidium which is a species of Trentepohlia. Genera and species are 

largely corticolous and the thallus is inconspicuous, often developing within 

the substratum. The perithecia, like those of Verrucariae, are immersed or 

partly emergent and have an entire or dimidiate outer wall. They are 

scattered over the thallus except in Anthracothecium where they are often 

coalescent. This genus is tropical or subtropical except for one species 

which inhabits S.W. Ireland. 

Paraphyses are variable, and in some species tend to disappear, but do 

not dissolve in mucilage. The spores are generally colourless, only in one 

monotypic genus, C&ccotrema, are they simple. The cells into which the 

spore is divided differ in form according to the genus. 

Paraphyses branched and entangled or wanting. 

Perithecia opening above by stellate lobes i. *Asteroporum Miill.-Arg. 

Perithecia opening by a pore. 

Spores variously septate. 

Spore cells cylindrical or cuboid. 

Spores colourless, elongate or ovate i-5-septate 2. Arthopyrenia Massal. 

Spores colourless, filiform I -multi-septate 3. Leptorhaphis Koerb. 

Spores colourless, muriform 4. Polyblastropsis A. Zahlbr. 

Microthelia Koerb. 

Spores brown, ovoid or elongate 2-5-septate ... 

5. 

Spore cells globose or lentiform, 3-multi-septate 6. *Pseudopyrenula Miill.-Arg. 

Paraphyses unbranched free. 


Perithecia beset with hairs 7. *Stereochlamys Miill.-Arg. 

Perithecia naked. 

Asci disappearing ; spores elongate multi- 

septate, colourless 

Asci persistent. 

8. *Belonia Koerb. 

Spores simple, ellipsoid, colourless 9. *Coccotrema Miill.-Arg. 

Spores elongate, i-multi-septate, colourless... 10. Porina Miill.-Arg. 

Spores elongate, i -multi -septate, brown u. Blastodesmia Massal. 

Spores muriform, colourless 12. *Clathroporina Miill.-Arg. 

Spores elongate, 2-3-septate, colourless Spore 

13. Thelopsis Nyl. 

cells globose or lentiform. 

Spores elongate, i-5-septate, brown 14. Pyrenula Massal. 

Spores muriform, brown 15. Anthracothecium Massal. - 

VIII. PARATHELIACEAE 

This family is peculiar in that the perithecia open by a somewhat 

elongate ostiole that slants at an oblique angle. The algal cells are Trente- 

pohlia. Genera and species are endemic in tropical or subtropical regions 

of the Western hemisphere, though a species of Pleurotrema has been found 

in subantarctic America. They are corticolous and the thallus is either


superficial or embedded. The genera are arranged according to spore 

characters : 

Spores elongate, 2- or more-septate. 

Spore cells cylindrical, colourless i. *Pleurotrema Miill.-Arg. 

Spore cells globose-lentiform. 

Spores colourless 2. *Plagiotrema Miill.-Arg. 

Spores brown 3. *Parathelium Miill.-Arg. 

Spores muriform. 

Spores colourless 4. *Campylothelium Mull.-Arg. 

Spores brown 5. *Pleurothelium Miill.-Arg. 

IX. TR YPETHEL IA CEA E 

This and the following two families are distinguished by the pseudo- 

stroma or compound fruit, a character rare among lichens, though the true 

stroma is frequent in Pyrenomycetes in such genera as Dothidea, Valsa, etc. 

The genera are crustaceous and corticolous and occur with few exceptions 

in tropical or subtropical regions, mostly in the Western Hemisphere. 

Several grow on officinal bark (Cinchona, etc.). Algal cells are Trentepohlia. 

As in many tropical lichens, the spores are large. The genera are based 

chiefly on spore characters, on septation, and on the form of the spore 

cells : 


Spores colourless, elongate, multi-septate i. *Tomasiella Miill.-Arg. 

Spores colourless, muriform 2. *Laurera Rehb. 

Spores brown, muriform 3. *Bottaria Massal. 


Spores colourless, elongate, multi-septate 4. *Tr\ pethelium Spreng. 

Spores brown, elongate, multi-septate 5. Melanotheca Miill.-Arg. 

X. ASTROTHELIACEAE 

The perithecia are either upright or inclined, and occur usually in 

radiate groups. They are free or united in a stroma, and the elongate 

ostioles open separately or coalesce in a common canal. The genera are 

all crustaceous, with Trentepohlia gonidia. They are tropical or subtropical, 

mostly in the Western Hemisphere; but species of Parmentaria and Astrothelium 

have been recorded also from Australia. 

The spores are all many-celled and the form of their cells is a generic 

character : 

' 

Spores elongate, multi-septate. 

Spore cells cylindrical 


I- *Lithothelium Miill.-Arg. 

colourless 2. *Astrothelium Trev. 

Spores 

Spores brown 3- *Pyrenastrum Eschw. 


Spores colourless 4- *Heufleria Trev. 

Spores brown 5- *Parmentaria Fe'e.

3 i8 

SYSTEMATIC 

XL MYCOPORACEAE 

A small family with only two genera which are found in both Hemispheres 

; species of both occur in Great Britain. They are all corticolous. 

The perithecia 

are united into a partially chambered fruiting body surrounded 

by a common wall, but opening by separate ostioles. The thallus is thinly 

crustaceous, with Palmella gonidia in Mycoporum, and Trentepohlia in 

Mycoporellum. The spores are colourless or brown in both genera : 

Spores muriform i. Mycoporum Flot. 

Spores elongate, multi-septate 2. Mycoporellum A. Zahlbr. 

XII. PHYLLOPYRENIACEAE 

Thallus foliose with both surfaces corticate and attached by rhizinae. 

Algal cells Trentepohlia. There is but one genus, Lepolichen, which has a 

laciniate somewhat upward growing thallus. Two species, both from South 

America, have been described, L. granulatus Miill.-Arg. and L. coccophora 

Hue. The latter has been recently examined by Hue 1 who finds, on the 

thalli, cephalodia which are peculiar in containing bright-green gelatinous 

algae either Urococcus or Gloeocystis, 

one of the few instances known of 

chlorophyllaceous algae forming part of a cephalodium. Gloeocystis may be 

the only alga present in the cephalodium ; 

Urococcus is always accompanied 

by Scytonema. 

The perithecia are immersed in thalline tubercles : 

Spores colourless, simple, ovoid or ovoid-elongate I. *Lepolichen Trevis. 

XIII. STRIGULACEAE 

A family of epiphyllous lichens inhabiting and disfiguring coriaceous 

evergreen leaves, or occasionally fern leaves in tropical or subtropical regions. 

The algae associated are Mycoidea and Phycopeltis (Phyllactidium). The 

only truly parasitic lichen, Strigula, belongs to this family: the alga precedes 

the lichen on the leaves and is gradually invaded by the hyphae of the 

lichen and altered in character. The small black perithecia are scattered 

over the surface. In Strigula the lichen retains the spreading rounded form 

of the alga. The other genera are more irregular. 

Thallus orbicular in outline I. *Strigula Fries. 

Thallus irregular. 

Perithecia without hairs. 

Spores colourless. 

Spores elongate, multi-septate 2. *Phylloporina Mull.-Arg. 

Spores muriform 3. *Phyllobathelium Miill.-Arg. 

Spores brown. 

Spores simple 4. *Haplopyrenula Miill.-Arg. 

Spores elongate, [-3-septate 5. *Microtheliopsis Miill.-Arg. 

Perithecia beset with stiffhairs 6. *Trichothelium Miill.-Arg. 

1 Hue 1905.


XIV. PYRENWIACEAE 

The only family of Pyrenocarpineae associated with blue-green algae. 

The genera of Pyrenidiaceae are all monotypic, only one is common and 

of wide distribution, Coriscium (Normandina Nyl.). Pyrenidium is the only 

member that has a fruticose thallus, and that is of minute dimensions. 

Eolichen Heppii, found and described by Zukal, is a doubtful lichen. " 

Lophothelium 

" Stirton is a case of parasitism of a fungus, Ticothecium, on the 

squamules of Stereocaulon condensatum. 

Algal cells Scytonema or Stigonema. 

Thallus crustaceous 1 

; spores simple, colourless i. *Rhabdopsora Mull.-Arg. 

Thallus crustaceous ; spores i-septate, colourless 2. *Eolichen Zuk. 

Thallus crustaceous ; spores muriform, brown 3. *Pyrenothrix Riddle 2 . 

Thallus squamulose ; spores numerous, simple 4. *Placothelium Miill.-Arg. 

Algal cells Nostoc. 

Thallus crustaceous; spores filiform, simple, colourless 5. *Hassea A. Zahlbr. 

Thallus fruticose ; spores elongate, 3-septate, brown ...6. Pyrenidium Nyl. 

Algal cells Microcystis (Polycoccus). 

Thallus squamulose ; fructification unknown 7. Coriscium Wainio. 

SERIES II. GYMNOCARPEAE 

SUBSERIES i. Coniocarpineae 

This small subseries is marked by the peculiar "mazaedium" type of 

fruit with its disappearing asci. It forms a connecting link between the 

families with perithecia and those with apothecia. The thallus is crustaceous 

or fruticose, often poorly developed and sometimes absent. The algal cells 

are Protococcaceae or rarely Trentepohlia. 

XV. CALICEACEAE 

The thallus is thinly crustaceous, sometimes brightly coloured, some- 

times absent, taking no part in the formation of the fruits; these have 

upright stalks with a small capitulum, and often look like minute nails. 

One genus, Sphinctrina, is parasitic on the thallus of other lichens, mostly 

Pcrtusariae. 

Fruits with slender stalks. 


Spores colourless i. Coniocybe Ach. 

Spores brown 2. Chaenotheca Th. Fr. 

Spores septate, brown. 

Spores i-septate 3. Calicium De Not. 

Spores 3-7-septate 4- Stenocybe Nyl. 

Fruits with short thick stalks. 

Spores globose, brown (parasitic) 5- Sphinctrina Fries. 

Spores i-septate, brown 6. *Pyrgidium Nyl. 

1 

Zahlbr., in Hedwigia, LIX. p. 301, 1917. 

* Riddle 1917.

3 20 SYSTEMATIC 

XVI. CYPHELIACEAE 

Thallus crustaceous. Algal cells Protococcaceae or Trentepohlia. Apo- 

thecia sessile, more widely open than in the previous family; in some genera 

the thallus forms an outer apothecial margin. The genera Farriola from 

Norway and Tylophorella from New Granada are monotypic. The British 

genus Cyphelium has been known as Trachytia. 

Thallus with Protococcaceae. 

Spores colourless, simple i. *Farriola Norm. 

Spores brown, i-3-septate (rarely simple or - muriform) ...2. Cyphelium 

Thallus with Trentepohlia. 

Th. Fr. 

Spores simple, many in the ascus 3. *Tylophorella Wainio. 

Spores 8 in the ascus. 

Apothecia with a thalline margin 4. *Tylophoron Nyl. 

Apothecia without a thalline margin 5. *Pyrgillus Nyl. 

XVII. SPHAEROPHORACEAE 

The most highly evolved family of the subseries, as regards the thallus. 

Algal cells Protococcaceae. In Tkolurna, a small lichen endemic in Scandinavia, 

there is a double thallus : one of horizontal much-divided squa- 

mules, the other swollen, upright, terminating in the capitulum. The fruit 

is lateral in Calycidium, a squamulose form from New Zealand, and in 

Pleurocybe from Madagascar, with stiff strap-shaped fronds. All the genera 

are monotypic except Sphaerophorus, of which genus ten species are recorded, 

some of them with a world-wide distribution. The spores are brown and 

simple or I -septate. 

Thallus squamulose and upright i. *Tholurna Norm. 

Thallus wholly squamulose 

2. *Calycidium Stirton. 

Thallus fruticose. 

Fronds hollow in the centre 3. *Pleurocybe Miill.-Arg. 

Fronds not hollow. 

Fruit without a thalline margin 4. *Acroscyphus Lev. 

Fruit inclosed in the tip of the fronds 5. Sphaerophorus Pers. 

SUBSERIES i. Graphidineae 

In this subseries are included five families that differ rather widely from 

each other both in thallus and apothecia; the latter are more or less 

carbonaceous and mostly with a proper margin only. Families and genera 

are widely distributed, though most abundant in warm regions. Algal cells 

mostly Trentepohlia. 

A comprehensive study of the apothecia of this series by Bioret 1 

gives 

some interesting results in regard to the paraphyses: in Arthonia they are 

irregular in direction and much-branched ; in Opegrapha, the paraphyses 

are vertical and parallel with more regular branching ; Stigmatidium (Entero- 

1 Bioret 1914.


graplia} resembles Opegrapha in this respect as does also Platygrapha, a 

genus of Lecanactidaceae, while in Grapliis the paraphyses are vertical, 

unbranched and free; Melaspilea paraphyses are somewhat similar to those 

of Gr aphis. 

XVIII. ARTHONIACEAE 

The thallus of Arthoniaceae is corticolous with few exceptions and is 

very inconspicuous, being largely embedded in the substratum. The 

apothecia (ardellae) are round, irregular or stellate, without any margin, 

the hymenium being protected by the dense branching of the paraphyses 

at the tips. 

A rthonia is abundant everywhere. The species of the other genera belong 

mostly to tropical or subtropical countries. Arthoniopsis is similar to 

Arthonia in the character of the fruits, but the gonidium is a Phycopeltis, 

and it is only found on leaves. SynartJionia with peculiar stromatoid fruc- 

tification is monotypic; it occurs in Costa Rica. 

Apothecia scattered. 

Thallus with Trentepohlia gonidia. 

Spores elongate i- or pluri-septate 

i. Arthonia Ach. 

Spores muriform 2. Arthothelium Massal. 

Apothecia stromatoid. 

Spores elongate, multi-septate 3. *Synarthonia Mull.-Arg. 

Thallus with Pahnella gonidia. 

Spores i- or more-septate 4. Allarthonia Nyl. 

Spores muriform 5- *Allarthothelium Wain. 

Thallus with Phycopeltis gonidia. 

Spores elongate I- or more-septate 6. *Arthoniopsis Miill.-Arg. 

XIX. GRAPHIDACEAE 

Thallus crustaceous, inconspicuous, partly immersed, mainly growing 

on bark but occasionally on dead wood or stone. Algal cells chiefly 

Trentepohlia, very rarely Palniella or Phycopeltis (epiphyllous). Apothecia 

(lirellae) carbonaceous more or less linear, opening by a narrow slit with 

a well-developed proper margin except in Gymnographa, a monotypic 

Australian genus. In two genera, the fruit is of a compound nature, several 

parallel discs occurring in one lirella: these are Ptychographa (on bark in 

Scotland) and Diplogramma (Australia), both are monotypic. They must 

not be confused with Graphis elegans and allied species in which the sterile 

carbonaceous margin is furrowed. Two tropical genera associated with 

Phycopeltis are epiphyllous. 

Graphidaceae are among the oldest recorded lichens, attention having 

been drawn to them since early times by the resemblance of the lirellae on 

the bark of trees to hieroglyphic writing.

322 

Apothecia single. 

Hypothec) urn dark-brown. 

SYSTEMATIC 

Thallus with Palmetto, gonidia. 

Spores simple 

colourless or brownish. 

i. Lithographa Nyl. 

Hypothecium 


Spores simple 2. Xylographa Fries. 

Spores elongate 3-8-septate 3. *Aulaxina Fee. 

Spores brown. 

Spores i -septate 4. Encephalographa Massal. 

Spores pluri-septate, then muriform 5. *Xyloschistes Wain. 

Apothecia compound. 

Spores simple, colourless 6. Ptychographa Nyl. 

Spores pluri-septate, colourless 7. *Diplogramma Miill.-Arg. 


Spores elongate i -multi-septate, the cells longer than wide. 

Spores brown. 

Spores i-(rarely more)-septate 8. Melaspilea Nyl. 

Spores 3-septate (apothecia rudimentary) 9. *Gymnographa Miill.-Arg. 


Spores acicular, coiled (many in the ascus) 10. *Spirographa A. Zahlbr. 

Spores fusiform, straight n. Opegrapha Humb. 

Spores muriform. , 

Spores elongate, central cells finally muriform 12. *Dictyographa Miill.-Arg. 

Spores elongate, septate, cells wider than long. 

Paraphyses unbranched, filiform. 

Spores multi-septate, colourless 13. Graphis Adans. 

Spores multi-septate, brown 14. Phaeographis Miill.-Arg. 

Spores muriform, colourless 15. Graphina Miill.-Arg. 

Spores muriform, brown 16. Phaeographina Miill.-Arg. 

Paraphyses clavate, warted at tips 17. *Acanthothecium Wain. 

Paraphyses branched, interwoven above 18. *Helminthocarpon Fe"e. 

Thallus with Phycopeltis gonidia (epiphyllous). 

Spores elongate, 3-9-septate, colourless 19. *Opegraphella Miill.-Arg. 

Spores elongate, i-septate, brown 20. *Micrographa Miill.-Arg. 

XX. CHIODECTONACEAE 

Specially distinguished in this subseries by the grouping of the somewhat 

rudimentary apothecia in pseudostromata in which they are almost wholly 

immersed. In form they are roundish or linear; the spores are septate or 

muriform. The thallus is thinly crustaceous and continuous : in Glyphis, 

Sarcographa and Sarcographina there is an amorphous upper cortex, the 

other genera are non-corticate. Algal cells are Trentepohlia with the 

exception of two epiphyllous genera associated with Phycopeltis. 

Genera and species are mostly tropical. Sderophyton with five species 

is represented in Europe by a single British specimen, S. circumscriptum. 

The form of the paraphyses is a distinguishing character of the genera.



Paraphyses free, unbranched. 

Spore cells short or almost globose. 

Spores elongate, multi-septate, colourless i. Glyphis Fe"e. 

Spores elongate, multi-septate brown 2. *Sarcographa Fe"e. 

Spores muriform, brown 3. *Sarcographina Miill.-Arg. 

Spore cells longer and cuboid. 

Spores muriform, colourless 4. *Enterodictyon Miill.-Arg. 

Paraphyses branched, interwoven above. 

Spores elongate, multi-septate, colourless 5. Chiodecton Ach. 

Spores elongate, multi-septate, brown 6. Sclerophyton Eschw. 

Spores muriform, colourless 7. *Minksia Miill.-Arg. 

Spores muriform, brown 8. *Enterostigma Miill.-Arg. 

Paraphyses free. 

Thallus with Phycopeltis gonidia (epiphyllous). 

Spores unequally 2-celled, colourless 

Paraphyses branched, interwoven above. 

9. *Pycnographa Miill.-Arg. 

Spores elongate, multi-septate, colourless 10. *Mazosia Massal. 

XXI. DlRINACEAE 

A small family, which is associated with and often included under 

Graphidaceae. The thallus is crustaceous and corticate on the upper 

surface, the cortex being formed of palisade hyphae. Algal cells Trente- 

polilia. Apothecia are rounded or with a tendency to elongation, and, in 

addition to a thin proper margin, possess a stout thalline margin ; the 

hypothecium is thick and carbonaceous. There are two Dirinastrum 

: genera 

with twelve species has a wide distribution ; 

Dirina 

is monotypic and 

occurs on maritime rocks in Australia. In both the spores are elongate- 

septate, differing only 

Spores 

in colour : 

colourless I. Dirina Fr. 

Spores brown 2. *Dirinastrum Miill.-Arg. 

XXII. ROCCELLACEAE 

The Roccellaceae differ from the preceding Dirinaceae chiefly in the 

fruticose thallus which is more or less characteristic of all the genera, though 

in Roccellographa it expands into foliose dimensions and in Roccellina is 

reduced to short podetia-like processes from a crustose base. The fronds 

mostly long and strap-shaped are protected in most of the genera by 

a cortex of compact palisade hyphae; in a few the outer hyphae are parallel 

with the long axis. The medulla is of parallel hyphae, either loose or 

compact. The algal cells are Trentepohlia. 

The apothecia are lateral except in Roccellina where they occur at the 

tips of the short upright fronds, and only in Roccellaria is there no thalline 

margin. They are superficial in all of the genera except Roccellographa, in 

which they are immersed and almost closed, recalling the perithecia-like

3 24 

SYSTEMATIC 

fruits of Chiodecton (sect. Enterographa). The spores are elongate, narrow, 

pluri-septate, and colourless or brownish, except in Darbishirella in 

they are ovoid, 2-septate and brown. 

which 

The affinity of Dirinaceae and Roccellaceae with Graphidaceae was first 

indicated by Reinke 1 and elaborated later by Darbishire 2 in his monograph 

of Roccellaceae. The apothecia in some species of Dirina are ellipsoid rather 

than round ; in several genera of Roccellaceae they are distinctly lirellate, 

and in Roccella itself some species have ellipsoid fruits. The fruticose thallus 

is predominant in Roccellaceae, but its evolution from the crustaceous type 

may be traced through Roccellina which is partly crustaceous and only 

imperfectly fruticose. 

In most of the genera only one species is recorded. Roccella, represented 

by twelve species, is well known for its dyeing properties, and has a wide 

distribution. Like other Graphidineae they are mainly plants of warm 

regions, mariy of them exclusively maritime rock-dwellers. 

The following synopsis of the genera is the one given by Darbishire in 

his monograph. 

Cortex fastigate, of palisade hyphae. 


Hypothecium black-carbonaceous. 

Apothecia round. 

Thallus fruticose I. Roccella DC. 

Thallus crustaceous-fruticose 2. *Roccellina Darbish. 

Apothecia lirellate Hypothecium 

3. *Reinkella Darbish. 

colourless. 

Gonidia present under the hypothecium 4. *Pentagenella Darbish. 

Gonidia absent from hypothecium 5. *Combea De Not. 

Spores brown or brownish. 

Medulla of parallel somewhat loose hyphae 6. *Schizopelte Th. Fr. 

Medulla solid, black 7. *Simonyella Steiner. 

Cortex fibrous, of parallel hyphae. 

Apothecia round. 

Hypothecium black-carbonaceous. 

Apothecia with thalline margin ; 

. . . 8. *Dendrographa Darbish. 

Apothecia with proper margin 9. *Roccellaria Darbish. 

Hypothecium colourless 10. *Darbishirella A. Zahlbr. 

Apothecia lirellate II. *Ingaderia Darbish. 

SUBSERIES 3. 


This last subseries includes the remaining twenty-nine families of Asco- 

lichens. They are very varied both in the fungal and the algal symbionts. 

The fruit is more or less a discoid open apothecium. The gonidia belong to 

different genera of Myxophyceae and Chlorophyceae, but the most frequent 

are Protococcaceae. Families are based largely on thalline structure. 


2 Darbishire 1898.


XXIII. LECANACTIDACEAE 

By many systematists this family is included under Graphidineae on 

account of the fruit structure which in some of the forms is carbonaceous 

and almost lirellate, and also because the algal symbiont is Trentepohlia. 

The thallus is primitive, being thinly crustaceous and non-corticate ; the 

apothecium has a black carbonaceous hypothecium in two of the genera, 

Lecanactis and Schismatomma (Platygrapha)\ in the third genus, Melampydiwn, 

it is colourless. The latter is monotypic, and the spores become 

muriform. In the other genera they are elongate and multi-septate. 

Apothecia with prominent proper margin i. Lecanactis Eschw. 

Apothecia with thin proper margin 2. *Melampydium Miill.-Arg. 

Apothecia with thalline margin 3. Schismatomma Flot. 

XXIV. PlLOCARPACEAE 

A small family with but one genus, Pilocarpon. It is distinguished as 

one of the few epiphyllous genera of lichens associated with Protococcaceous 

gonidia and with a distribution extending far beyond the tropics. The best 

known species, P. leucoblepJiarum, encircles the base of pine-needles with 

a white felted crust, or inhabits coriaceous evergreen leaves. Another species 

lives on fern leaves. The fruit is a discoid apothecium with a dark carbona- 

ceous hypothecium and proper margin, and with a second thalline margin. 

The paraphyses are branched and interwoven above. 

Spores elongate, 3-septate, colourless i. Pilocarpon Wain. 

XXV. CHRYSOTRICHACEAE 

This family now, according to Hue 1 

, 

includes two genera, Crocynia and 

with Protococ- 

Chrysothrix. In both there is a thallus of interlaced hyphae 

caceous algae scattered through it or in groups. The structure is thus 

homoiomerous, and Hue has suggested for it a new series, "Intertextae." 

The only British species, Crocynia lanuginosa, first 

2 

placed by Nylander in 

Amphiloma and later transferred by him to Leproloma*, has a soft crustaceous 

lobate thallus, furfuraceous on the surface; no fructification has been found. 

A West Indian species, C. gossypina, has discoid apothecia with a thalline 

margin. There is only one species of Chrysothrix, Ch. nolitangere, which 

forms small clumps or tufts on the spines of Cactus in Chili. The structure 

is somewhat similar to that of Crocynia. 

Spores colourless, simple 

Spores colourless, 2-3-septate 

1 Hue 1909. 


i- Crocynia Nyl. 

2. *Chrysothrix Mont. 

3 Nylander 1883.

326 

SYSTEMATIC 

XXVI. THELOTREMACEAE 

A tropical or subtropical family of which the leading characteristic is 

the deeply sunk disc of the apothecium : 

it has a proper hyphal margin, 

and, round that, an overarching thalline margin. The apothecia occur singly, 

or they are united in a kind of : pseudostroma in Tremotylium several grow 

together, while in Polystroma each new apothecium develops as an outgrowth 

from the thalline margin of the one already formed, so that an upright, 

branching succession of fruits is built up. It is a very unusual type of lichen 

fructification, with one species, P. Ferdinandezii, found in Spain and in 

Guiana. 

The thallus in all the genera is crustaceous with an amorphous (decom- 

posed) cortex; or it is non-corticate. The algal cells are Trentepohlia except 

in Phyllophthalmaria, an epiphyllous genus associated with the alga Phycopeltis. 

In Polystroma the alga is unknown. 

Only one genus is represented in the British Isles. 

Apothecia growing singly. 


Paraphyses numerous, unbranched, free. 


Spores elongate, 2- or multi-septate i. *Ocellularia Spreng. 

Spores muriform 2. Thelotrema Ach. 

Spores brown. 

Spores elongate, septate .3. *Phaeotrema Miill.-Arg. 

Spores muriform 4. *Leptotrema Mont. 

Paraphyses scanty, branched. 

Spores muriform, brown 5- *Gyrostomum Fr. 

Thallus with Phycopeltis gonidia 6. *Phyllophthalmaria A. Zahlbr. 

Apothecia in pseudostromata. 

Apothecia united in tubercles 7. *Tremotylium Nyl. 

Apothecia united 'by the margins 8. *Polystroma Clem. 

XXVII. DlPLOSCHISTA CEA E 

Scarcely differing from the preceding family except in the gonidia which 

are Protococcaceous algae. The thallus is crustaceous and non-corticate. 

The apothecia have a double margin but the outer thalline margin is less 

overarching than in Thelotremaceae. The spores in the two genera are 

somewhat peculiar: in Conotrema they are exceedingly long and divided 

by parallel septa into thirty to forty small cells ; in Diploschistes ( Urceolaria) 

they are large, muriform and brown. Conotrema contains two corticolous 

species ; Diploschistes about thirty species mostly saxicolous. Both genera 

are represented in the British Isles. 

Spores elongate, multi-septate, colourless i. Conotrema Tuck. 

Spores muriform, brown 2. Diploschistes Norm. 

t


XXVIII. ECTOLECHIACEAE 

A family of tropical epiphyllous lichens that are associated with Proto- 

coccaceous gonidia. The thallus is primitive in character, mostly a weft of 

hyphae with intermingled algal cells, described as homoiomerous. 

The apothecia are without a thalline margin, and with a scarcely 

developed proper margin : 

their affinity is with the Lecideaceae, though in 

two genera, Lecaniella and ArtJiotJieliopsis, there are gonidia below the 

hypothecium, a character of Lecanoraceae. The genera are nearly all 

monotypic ; in Sporopodium has been included Lecidea phyllocJiaris YVainio 

(Sect. Gonotheciuni), which is distinguished by hymenial gonidia. 

Apothecia at first covered by a "veil." 

Spores elongate, colourless, i. septate *Asterothyrium Mull.-Arg. 

uncovered from the first. 

Apothecia 

Gonidia not present below the hypothecium. 

Paraphyses unbranched, free. 

Spores muriform 2. *Lopadiopsis Wain. 

Paraphyses branched. 

Spores i-septate 3. *Actinoplaca Mi.ill.-Arg. 

Spores elong'ate, multi-septate 4. *Tapellaria Miill.-Arg. 

Spores muriform 5. *Sporopodium Mont. 

(ionidia present below the hypothecium. 

Spores elongate, 2-septate 6. *Lec'aniella Wain. 

Spores muriform 7. *Arthotheliopsis Wain. 

XXIX. GYALECTACEAE 

The algal cells in this family are filamentous; either Myxophyceae 

(Scytoneina) or Chlorophyceae ( Trentepohlia or Phyllactidium). The thallus 

is crustaceous, and in some cases homoiomerous, as in Petractis, where the 

alga, Scytonema, penetrates the substratum as deeply as the hyphae. Mono- 

phiale, a tropical genus, possesses two kinds of : gonidia the species that 

grow on bark or mosses are associated with Trentepohlia ; others that have 

invaded the surface of leathery evergreen leaves resemble most epiphyllous 

lichens in being associated with the leaf alga Phyllactidium (Phycopeltis). 

Some species of Trentepohlia exhale when moist an odour of violets. This 

scent is retained in at least one genus, Jonaspis. 

The apothecia are superficial, and are soft, waxy and bright-coloured, 

with prominent margins which are however entirely hyphal : 

the affinity is 

therefore with Lecideaceae. In one genus, Sagiolechia, the fruit is carbona- 

ceous and dark coloured. The spores of all the genera are colourless. 

Apothecia waxy, bright-coloured. 

Thallus with Scytonema. gpnidia. 

Spores elongate, 3-septate i. Petractis Fr.

328 

Thallus with Trentepholia gonidia. 

Asci 6-8-spored. 

SYSTEMATIC 

Spores simple 2. Janaspis Th. Fr. 

Spores i-septate 3. *Microphiale A. Zahlbr. 

Spores septate or muriform 

Asci i2-many-spored. 

4. Gyalecta Ach. 

Spores i-septate 5. *Ramonia Stizenb. 

Spores fusiform or acicular, many-septate ...6. Pachyphiale Lonnr. 

Apothecia carbonaceous. 

Spores elongate, 2-3-septate 

7. *Sagiolechia Massal. 

XXX. COENOGONIACEA E 

There are only two genera in this small family, Coenogonium with Trente- 

pohlia gonidia, and Racodium with Cladophora. Both genera follow the algal 

form and are filamentous. In Coenogonium the filaments are sometimes 

matted into a loose felted expansion. The genus is mainly tropical or 

subtropical and mostly rather light-coloured. There is only 

species, 

one British 

1 

C. ebeneum a sterile , form, in which the hyphae are very dark-brown ; 

it often covers large areas of stone or rock with its sooty-like creeping 

filaments. 

Racodium includes 2 (?) species. One of these, R. rupestre, is sterile and 

resembles C, ebeneum in form and colour. 

The apothecia of Coenogonium are waxy and light-coloured ; they are 

borne laterally on the filaments; the spores are simple or I -septate. 

Thallus with Trentepohlia gonidia i. Coenogonium Ehrenb. 

Thallus with Cladophora gonidia 2. Racodium Fr. 

XXXI. LECIDEACEAE 

One of the largest lichen families as regards both genera and species, 

and of world-wide distribution. The algal cells are Protococcaceae. The 

thallus is mostly crustaceous but it becomes squamulose in Psora, a section 

of Lecidea\ and in Sphaerophoropsis, a Brazilian genus, there are small 

upright fronds or stalks with lateral apothecia. The prevailing colour of 

the thallus is some shade of grey, but it ranges from white or yellow to 

dark-brown or almost black. Cephalodia appear in some of the species. 

The apothecia have a proper margin only, no gonidia taking part in the 

fruit-formation. They may be soft and waxy (biatorine) or hard and 

carbonaceous (lecideine). The genera are mainly based on spore characters 

which are very varied. 

The arrangement of genera given below follows that of Zahlbruckner ; 

in several instances, both as to the limitations of genera and to the nomen- 

clature, it differs from that of British text-books, though the general principle 

of classification is the same. 

1 Lorrain Smith 1906.

Thallus crustaceous non-corticate. 


Spores small, thin-walled. 

Spores 


colourless i. Lecidea Ach. 

Spores brown 2. *Orphniospora Koerb. 

Spores large, thick-walled 3. Mycoblastus Norm. 

Spores i -septate. 

Spores small, thin-walled 4. Catillaria Th. Fr. 

Spores large, thick-walled 5. Megalospora Mey. and Flot. 

Spores elongate, 3-multi-septate. 

Spores elongate, narrow, thin-walled 6. Bacidia A. Zahlbr. 

Spores elongate, large and thick- walled 7. Bombyliospora De Not. 


Spores colourless; on trees 8. Lopadium Koerb. 

Spores colourless to brown ; on rocks 9. Rhizocarpon Th. Fr. 

Thallus warted or squamulose, corticate. 

Spores elongate, i-y-septate, thin- walled 

Thallus of upright podetia-like small fronds. 

10. Toninia Th. Fr. 

n. *Sphaerophoropsis Wain. 

Spores ellipsoid, becoming I -septate 

XXXII. PHYLLOPSORACEAE 

A small family of exotic lichens with a somewhat more developed thallus 

than that of the Lecideaceae, being in both of the genera squamulose or 

almost foliose. 

The apothecia are without a thalline margin ; they 

lecideine ; the 

are biatorine or 

hypothecium is formed of plectenchyma and is purple-red 

in one species, Phyllopsora furfuracea. The two genera differ only in spore 

characters. There are fifteen species, mostly corticolous, belonging to 

Pliyllopsora ; only one, from New Zealand, 

is recorded for Psorella. 

Spores simple i. *Phyllopsora Miill.-Arg. 

Spores elongate, septate 2. *Psorella Miill.-Arg. 

XXXIII. CLADONIACEAE 

Associated with Lecideaceae in the type of apothecium, but differing 

widely in thallus formation. The latter is of a twofold type : the primary 

thallus is crustaceous, squamulose, or very rarely foliose ; the secondary 

thallus or podetium, upright, simple or branched, is terminated by the 

apothecia, or broadens upwards to cup-like scyphi. Algal cells, Protococ- 

caceae, according to Chodat, Cystococcus. 

Much attention has been given to the origin and development of the 

podetia in this family. They are superficial on granule or squamule 

except in the monotypic Himalayan genus Gymnoderma where they are 

marginal on the large leaf-like lobes. Though in origin the podetia are 

doubtless fruit stalks, they have become in most cases vegetative in function.

330 

SYSTEMATIC 

The fruits are coloured yellowish, brown or red (or dark and carbonaceous 

in Pilophorus), and are borne on the tips of the branches or on the margins 

of the scyphi. In Glossodium and Thysanothecium the former from New 

Granada, the latter from Australia the apothecia occupy one side of the 

widened surface at the tips. 

Cephalodia are developed on the primary thallus of Pilophorus, and on 

the podetia of Stereocaulon and Argopsis. 

Podetia simple, short, not widening upwards. 

Podetial stalks naked. 

Primary thallus thin, continuous I. Gomphillus Nyl. 

Primary thallus granular or squamulose ... 2. Baeomyces Pers. 

thallus foliose. 

Primary 

Podetia superficial 3. *Heteromyces Miill.-Arg. 

Podetja marginal 4. *Gymnoderma 1 

Nyl. 

Podetial stalks granular, squamulose 5. Pilophorus Th. Fr. 

Podetia short, widening upwards. 

Podetia simple above, rarely divided 

Podetia lobed, leaf-like 

... 6. *Glossodium Nyl. 

7. *Thysanothedum Berk. & Mont. 

Podetia elongate, variously branched, or scy-1 ' 

\ 

and hollow J 

phous 

Podetia elongate, not scyphous, the stalks solid. 

8. Cladoma Hill, 

Spores elongate, septate 9. Stereocaulon Schreb. 

Spores muriform 10. *Argopsis Th. Fr. 

XXXIV. GYROPHORACEAE 

A small family of foliose lichens allied to Lecideaceae by the character 

of the fruit a superficial apothecium in the formation of which the gonidia 

take no share. There are only three genera, distinguished by differences in 

spore and other characters. Dermatiscum has light-coloured thallus and 

fruits ; of the two species, one occurs in Central Europe, the other in North 

America. Umbilicaria and GyropJiora are British; they are dark-coloured 

rock-lichens and are extremely abundant in Northern regions where they 

are known as "tripe de roche." Algal cells Protococcaceae. 

Umbilicaria, Dermatiscum, and some species of Gyrophora are attached 

to the substratum by a central point. Other species of Gyrophora are 

rhizinose. In all there is a cortex of plectenchyma above and below. In 

Gyrophora the thallus may be monophyllous as in Umbilicaria, or polyphyllous 

and with or without rhizinae. New lobes frequently arise from 

protuberances or warts on the older parts of the thallus. At the periphery, 

in most species, growth is equal along the margins, in G. erosa 2 the edge is 

formed of numerous anastomosing lobes with lateral branching, the whole 

forming a broadly meshed open network. Further back the tissues become 

continuous owing to the active growth of the lower tissue or hypothallus, 

1 

Neophyllis Wils. is synonymous with Gymnoderma. 

2 Lindau 1 899.


which grows out from all sides and meets across the opening. The overlying 

layers, with gonidia, follow more slowly, but they also in time become 

continuous, so that the "erose" character persists only near the periphery. 

This forward growth of the lower thallus occurs in other species, though to 

a much less marked degree. 

There is abundant detritus formation in this family; the outer layers of 

the cortex are continually being sloughed, the dead tissues lying on the 

upper surface as a dark gelatinous layer, continuous or in small patches. 

On the under surface the cast-off cortex gathers into a loose confused mass 

of dead tissues. 

Asci 8-spored. 

Spores mostly simple (disc gyrose) i. Gyrophora Ach. 

Spores i-septate 2. *Dermatiscum Nyl. 

Asci i-2-spored. 

Spores muriform 3. Umbilicaria Hoffrn. 

XXXV. ACAROSPORACEAE 

Thallus foliose, squamulose or crustaceous, sometimes scarcely developed. 

Algal cells Protococcaceae. 

Into this family Zahlbruckner has gathered the genera in which the 

asci are many-spored, as he considers that a character of great importance 

in determining relationship, but he has in doing so overlooked other very 

great differences. The fruit-bodies are round and completely enclosed in 

a thalline wall in Thelocarpon, which has however no perithecial wall. They 

have a proper margin only (lecideine) in Biatorella, and a thalline margin 

(lecanorine) in the remaining genera. In Acarospora the apothecia are sunk 

in the thallus. Stirton's genus Cryptothecia^ is allied to Tfielocarpon 

in the 

fruit-formation, but the basal thallus is well developed and the spores are 

few in number and variously divided. 

Thallus none. 

Apothecia (or perithecia) in thalline warts i. Thelocarpon Nyl. 

Thallus crustaceous. 

Apothecia lecideine ; spores simple 2. Biatorella Th. Fr. 

Apothecia lecanorine ; spores septate 3. 

*Maronea Massal. 

Thallus of small squamules 4. Acarospora Massal. 

Thallus almost foliose, attached centrally 5. *Glypholecia Nyl. 

XXXVI. EPHEBACEAE 

A family of very simple structure either filamentous, foliose or crustaceous. 

The algal cells which give a dark colour to the thallus are Stigonema or 

Scytonema, members of the blue-green Myxophyceae, and consist of minute 

simple or branched filaments single cell-rows in Scytonema, compound in 

Stigonema. 

1 Stirton 1877, p. 164.

33 2 SYSTEMATIC 

In some of the genera the lichen hyphae travel within the gelatinous 

sheath of the filaments, both algae and hyphae increasing by apical growth 

so that filaments many times the length of the alga are formed as in 

Ephebe. In others the filaments scarcely increase beyond the normal size 

of the alga as in Thermutis (Gonionema); or the gelatinous algal cells may 

be distributed in a stratum of hyphae. 

The apothecia are minute and almost closed; they may be embedded 

in swellings of the thallus, or are more or less superficial. The spores are 

rather small, colourless and simple or I -septate. 

The lichens of this family are rock-dwellers and are mostly to be found 

in hilly or Alpine regions. A tropical species, Leptogidium dendriscum, occurs 

in sterile condition in south-west Ireland. There are few species in any of 

the 'genera. 

Algal cells Scytonema. 

Thallus minutely fruticose, non-corticate I. Thermutis Fr. 

Thallus minute, of felted filaments, cortex one) _ ,, . 

7 

> 2. *Leptodendnscum Wain, 

cell thick I 

Thallus of elongate filaments, cortex of several cells 3. Leptogidium Nyl. 

Thallus foliose or fruticose, cellular throughout 4. Polychidium Ach. 

Thallus crustaceous, non-corticate 5. Porocyphus Koerb. 

Algal cells Stigonema. 

Thallus minutely fruticose, non-corticate 6. Spilonema Born. 

Thallus of long branching .filaments. 

Spores septate ; paraphyses wanting 7. Ephebe Fr. 

Spores simple ; paraphyses present 8. Ephebeia Nyl. 

Thallus crustaceous; upper surface non-corticate,! 

. \ 

lower surface corticate J 

. . . 

9. *Pterygtopsis Wain, 

XXXVII. P YRENOPSIDA CEA E 

In this family are included gelatinous lichens of which the gonidium is 

a blue-green alga with a thick gelatinous coat, either Gloeocapsa (including 

Xanthocapsd) or Chroococcus. In Gloeocapsa and Chroococcus the gelatinous 

envelope is often red, in Xanthocapsa it is yellow, and these colours persist 

more or less in the lichens, especially in the outer layers. 

The thallus is in many cases a formless gelatinous crust of hyphal 

filaments mingling with colonies of algal cells as in Pyrenopsis; but small 

fruticose tufts are characteristic of Synalissa, and larger foliose and fruticose 

thalli appear in some exotic genera. A plectenchymatous cortex is formed 

on the thallus of Forssellia, a crustaceous genus from Central Europe, with 

two species only; the whole thallus is built up of a kind of plectenchyma 

in some others, but in most of the genera there is no tissue formed. 

The apothecia, as in Ephebaceae, are generally half-closed.

Thallus with Gloeocapsa gonidia. 



Spores simple i. Pyrenopsis Nyl. 

Spores i-septate 2. -Cryptothele Forss. 

Thallus shortly fruticose 

3. Synalissa Fr. 

Thallus lobate, centrally attached 4. *Phylliscidium Forss. 

Thallus with Chroococcus gonidia. 

Thallus crustaceous 5. Pyrenopsidium Forss. 

Thallus lobate, centrally attached 6. *Phylliscum Nyl. 

Thallus with Xanthocapsa gonidia. 


Thallus non-corticate. 


Apothecia open, asci 8-spored 7. Psorotichia Forss. 

Apothecia covered, asci many-spored 8. *Gonohymenia Stein. 


Apothecia closed 9. *Collemopsidium Nyl. 

Thallus with plectenchymatous cortex 10. *Forssellia A. Zahlbr. 

Thallus lobate, centrally attached. 


Thallus plectenchymatous throughout 

u. *Anema Nyl. 

Thalline tissue of loose hyphae 

12. *Thyrea Massal. 

Cortex of upright parallel hyphae 13. *Jenmania Wacht. 


Thalline tissue of loose hyphae 14. *Paulia Fe"e. 

Thallus fruticose. 

Thallus without a cortex 15. *Peccania Forss. 

Thallus with cortex of parallel hyphae 

XXXVIII. LlCHlNACEAE 

16. *Phloeopeccania Stein. 

The only family of lichens associated with Rivularia gonidia, the 

trichomes of which retain their filamentous form to some extent in the 

more highly developed genera; they lie parallel to the long axis of the 

squamule or of the frond except in LicJiinella in which genus they are 

vertical to the surface. The thallus may be crustaceous, or minutely foliose, 

or fruticose; in all cases it is dark-brown in colour, and the gelatinous 

character is evident in the moist condition. The best known British genus 

is Licliina which grows on rocks by the sea. 

The apothecia are more or less immersed in the tissue; in Pterygium and 

Steinera they are open and superficial (the latter monotypic genus confined 

to Kerguelen). They are also open in Lichinella and Homopsella^ both very 

rare genera. The spores are colourless and simple except in Pterygium arid 

Steinera where they are elongate, and i-3-septate. 

Thallus crustaceous squamulose. 

Apothecia immersed in thalline warts i. *Calothricopsis Wain. 

Apothecia superficial, with thalline margin 2. *Steinera A. Zahlbr. 

Apothecia superficial, without a thalline margin 3. Pterygium Nyl.

334 

Thallus of small fruticose fronds. 

SYSTEMATIC 

Gonidia occupying the central strand 4. *Lichinodium Nyl. 

Gonidia not in the centre. 

Apothecia immersed Apothecia superficial. 

5. Lichina Ag. 

Paraphyses present 

6. *Lichinella Nyl. 

Paraphyses absent 7. *Homopsella Nyl. 

XXXIX. CoLLEMACEAE 

The most important family of the gelatinous lichens and the most 

numerous. Collema is historically interesting as having first suggested the 

composite thallus. Algal cells, Nostoc, which retain the chain-like form 

except in Leprocollema, a doubtful member of the family. The thallus varies 

from indeterminate crusts to lobes of considerable size ; occasionally the 

lobes are narrow and erect, forming minute fruticose structures. In the 

more primitive genera the thallus is non-corticate, but in the more evolved, 

the apical cells of the hyphae coalesce to form a continuous cellular cortex, 

one or more cells thick, well marked in some species, in others rudimentary; 

the formation of plectenchyma also occurs occasionally in the apothecial 

tissues of some non-corticate species. 

The apothecia are superficial except in Pyrenocollema, a monotypic genus 

of unknown locality. They are generally lecanorine, with gonidia entering 

into the formation of the apothecium : in some genera they are lecideine or 

biatorine, being formed of hyphae alone. The spores are colourless and vary 

in form, size and septation. 

Apothecia immersed ; spores fusiform, i-septate i. *Pyrenocollema Reinke. 

Apothecia superficial. 

Thallus without a cortex. 

Spores simple, globose or ellipsoid. 

Thallus crustaceous 2. *Leprocollema Wain. 

Thallus largely squamulose-fruticose. 

Apothecia lecideine (dark-coloured) 3. *Leciophysma Th. Fr. 

Apothecia lecanorine 4. Physma Massal. 

Spores variously septate or muriform. 

Apothecia biatorine (light-coloured) 5. *Homothecium Mont. 

Apothecia lecanorine 6. Collema Wigg. 

Thallus with cortex of plectenchyma. 


Spores globose 7. Lemmopsis A. Zahlbr. 

Spores ellipsoid, with thick subverrucose wall... 8. *Dichodium Nyl. 

Spores vermiform, spirally curved 

Spores variously septate or muriform. 

9. *Koerberia Massal. 

Apothecia biatorine (light-coloured) 

10. *Arctomia Th. Fr. 

Apothecia lecanorine u. Leptogium S. F. Gray.


XL. HEPPIACEAE 

A family belonging to the "blue-green" series as it is associated with 

a gelatinous alga, Scytonema, but is of almost entirely cellular structure and 

is non-gelatinous. The thallus is squamulose or minutely foliose, or is formed 

of narrow almost fruticose lobes; the apothecia are semi-immersed; the asci 

are 4-many-spored. 

Heppia is a wide-spread genus both in northern and tropical regions 

with about forty species that live on soil or rock. So far, no representative 

has been recorded in our Islands. 

Spores simple, colourless, globose or ellipsoid i. *Heppia Naeg. 

Spores muriform, colourless, ellipsoid 2. *Amphidium 1 

Nyl. 

X L I . PAN\ARIACEAE 

The members of this family are also non-gelatinous, though for the most 

part associated with blue-green gelatinous algae, Nostoc or Scytonema. The 

gonidia are bright-green in the genera Psoroma and Psoromaria, the former 

often included under Lecanora, but too closely resembling Pannaria to be 

dissociated from that genus. 

The -thallus varies from being crustaceous to squamulose or foliose, and 

has a cortex of plectenchyma on the upper and sometimes also on the 

lower surface. The apothecia are superficial or lateral and with or without 

a thalline margin (lecanorine or biatorine), the spores are colourless. 

Zahlbruckner has included Hydrotkyria in this family. It is a monotypic 

aquatic genus found in North America and very closely allied to Peltigera. 

The British species of the genus, familiarly known as Coccocarpia, have 

been placed under Parmeliella, the former name being restricted to the 

tropical or subtropical species first assigned to Coccocarpia and distinguished 

by the cortex, the hyphae forming it lying parallel with the surface though 

forming a regular plectenchyma. 

An Antarctic lichen TJielidea corrugata with Palmetto, gonidia is doubt- 

fully included: the thallus is foliose, the apothecia biatorine with colourless 

i -septate spores. 

Thallus with bright-green gonidia. 

With Palmetto, i. *Thelidea Hue. 

With Protococcaceae. 

Apothecia non-marginate (biatorine) 2. *Psoromaria Nyl. 

Apothecia marginate 3. Psoroma Nyl. 

Thallus with Scytonema gonidia. 

Apothecia marginate, spores i-septate 4. Massalongia Koerb. 

Apothecia non-marginate ; spores simple. 

Upper surface smooth 5. *Coccocarpia Pers. 

Upper surface felted 6. *Erioderma Fe"e. 

1 A. Zalilbruckner, in Oesterr. hot. Zeitschr. 1919, p- 163.

336 

Thallus with Nostoc gonidia. 

SYSTEMATIC 

Apothecia marginate ; spores simple 7. Pannaria Del. 

Apothecia non-marginate ; spores various. 

Thallus crustaceous or minutely squamulose ... 8. Placynthium Ach. 

Thallus squamulose, cortex indistinct 9. *Lepidocollema Wain. 

Thallus squamulose or foliose, cortex cellular ...10. Parmeliella Miill.-Arg. 

Thallus foliose, thin veined below 11. *Hydrothyria Russ. 

XLII. STICTACEAE 

Thallus foliose, mostly horizontal, with a plectenchymatous cortex on 

both surfaces, a tomentum of hair-like hyphae taking the place of rhizinae 

on the lower surface. Algal cells Protococcaceae or Nostoc. Cephalodia and 

cyphellae or pseudocyphellae often present. Apothecia superficial or lateral ; 

spores colourless or brown, variously septate. 

The highly organized cortex and the presence of aeration organs 

cyphellae or pseudocyphellae which are almost solely confined to the 

genus Sticta give this family a high position as regards vegetative development. 

The two genera are of wide distribution, but Sticta is more abundant 

in the Southern Hemisphere. Lobaria pulmonaria is one of our largest 

lichens. 

Under surface dotted with cyphellae or pseudo-} 

, I. Sticta Schreb. 

cyphellae ... 

Under surface without these organs 2. Lobaria Schreb. 

XLII I. PELTIGERACEAE 

A family of heteromerous foliose lichens containing in some instances 

blue-green (Nostoc), in others bright-green (Protococcaceae) gonidia, and 

thus representing a transition between these two series. They have large 

or small lobes and grow on the ground or on trees. 

Cephalodia, either ectotrophic (Peltidea) or endotrophic (Solorina), occur 

in the family and further exemplify the capacity of the fungus hyphae to 

combine with different types of algae. 

The upper surface is a wide cortex of plectenchyma, which in some 

is continued below. In the non-corticate under surface 

forms (Nephromium) 

of Peltigera, the lower hyphae grow out in hairs or rhizinae, very frequently 

brown in colour. Intercalary growth of the upper tissues stretches the 

thallus and tears apart the lower under surface so that the hair-bearing 

areas become a network of veins, with the white exposed medulla between. 

In Peltigera canina there is further growth and branching of the hyphae in 

the veins, adding to the bulk of the interlacing ridges. 

From all other foliose lichens Peltigeraceae are distinguished by the 

flat wholly appressed or peltate apothecia without a thalline margin which 

arise mostly on the upper surface, but in Nephromium on the extreme


margin of the under surface, the tip of the fertile lobe in that case is turned 

back as the apothecium matures, so that the fruit eventually faces the light. 

In Nephroma has been included Eunephroma with bright-green gonidia and 

Nephromium with blue-green. 

Bitter 1 has recorded the finding of apothecia on the under surface of 

Peltigera malacea and not at the margin, as in Nephromium. The plant was 

otherwise normal and healthy. Solorinella, from Central Europe and 

Asteristion from Ceylon are monotypic genera with poorly developed thalli. 

Thallus poorly developed. 

Asci 6-8-spored; spores 3-5 -septate i. *Asteristion Leight. 

Asci many-spored ; spores i-septate 2. *Solorinella Anzi. 

Thallus generally well developed. 

Apothecia superficial, sunk in the thallus 3. -Solorina Ach. 

Apothecia terminal on upper surface of lobes 4. Peltigera Willd. 

Apothecia terminal on lower surface of lobes 5. Nephroma Ach. 

XLIV. PERTUSARIACEAE 

Thallus crustaceous, often rather thick and with an amorphous cortex 

on the upper surface. Algal cells Protococcaceae. Apothecia solitary or 

several immersed in thalline warts, generally with a narrow opening which 

barely exposes the disc, and which in one genus, Perforaria, is so small as 

and with 

almost to constitute a perithecium ; spores are often very large 

thick walls; some if not all are multinucleate and germinate at many points. 

In the form of the fruit, this family stands between Pyrenocarpeae and 

Gymnocarpeae, though more akin to the latter. Perforaria, with two species, 

belongs to New Zealand and Japan. 

Pertusaria has a world-wide distri- 

bution, and Varicellaria, a monotypic genus, with a very large two-celled 

spore, is an Alpine plant, recorded from Europe and from Antarctic 

America. 


Apothecia with pore-like opening I. *Perforaria Miill.-Arg. 

Apothecia with a wider opening 2. Pertusaria DC. 

Spores i-septate 3. Varicellaria Nyl. 

XLV. LECANORACEAE 

Thallus mostly crustaceous, occasionally squamulose or very rarely 

minutely fruticulose. The squamulose thallus is corticate above, the under 

surface appressed and attached to the substratum by penetrating hyphae, 

often effigurateat the circumference. Algal cells Protococcaceae. Apothecia 

well distinguished by the thalline margin; spores colourless, simple or 

variously septate or muriform. 

1 Bitter 1904*.

33 8 

SYSTEMATIC 

Lecanora, Ochrolechia, Lecania, Haematomma and Phlyctis are cosmo- 

politan genera, some of them with a very large number of species; the other 

genera are more restricted in distribution and generally with few species. 

The genus Candelariella is of uncertain position; the spores are 8 or 

many in the ascus and are simple or I -septate, and not unfrequently become 

polarilocular as in Caloplacaceae, but there is no parietin present. 

Algae distributed through the thallus. Algae restricted to a definite zone. 

Spores simple i. *Harpidium Koerb. 


Thallus grey, white or yellowish. 

Spores rather small \2. Lecanora Ach. 

Spores large 

Thallus bright yellow. 

3. Ochrolechia Massal. 

Spores simple or I -septate 4. Candelariella Miill.-Arg. 

Spores i-septate (rarely pluri-septate). 

Paraphyses free. 

Thallus squamulose, effigurate 5. Placolecania Zahlbr. 


Apothecial disc brownish 6. Lecania Zahlbr. 

Apothecial disc flesh-coloured 7. Icmadophila Trevis. 

Paraphyses branched, intricate 8. *Calenia Miill.-Arg. 

Spores elongate, pluri-septate. 

Apothecia superficial 9. Haematomma Massal. 

Apothecia immersed. 

Paraphyses free 10. *Phlyctella Miill.-Arg. 

Paraphyses branched, intricate 11. *Phlyctidia Miill-Arg. 


Apothecia superficial 

12. *Myxodictyon Massal. 

Apothecia immersed 13. Phlyctis Wallr. 

XLVI. PARMELIACEAE 

A very familiar family of foliose lichens. Genera and species are dorsi- 

ventral and stratose in structure, though some Cetrariae are fruticose in 

habit. Algal cells are Protococcaceae; in Physcidia they are Palmellae, In 

every case the upper surface of the thallus is corticate and generally of 

plectenchyma, the lower being somewhat .similar, but in Heterodea and 

Physcidia, monotypic Australasian genera, the upper cortex is of branching 

hyphae parallel with the surface, the lower surface being non-corticate. 

The Parmeliae are mostly provided with abundant rhizinae; in Cetrariae 

and Nephromopsis these are very sparingly present, while in Anzia (including 

Pannopannelid) the medulla passes into a wide net-like structure of anasto- 

mosing hyphae. 

In Heterodea, cyphellae occur on the under surface as in Stictaceae; and 

in Cetraria islandica bare patches have been described as pseudocyphellae. 

The latter lichen is one of the few that are of value as human food. Special 

aeration structures are present on the upper cortex of Parmelia aspidota.

Thallus non-corticate below. 


Apothecia terminal I. *Heterodea Nyl. 

Apothecia superficial 2. *Physcidia Tuck. 

Thallus spongy below 3. *Anzia Stizenb. 

Thallus corticate below. 

Asci poly-spored 4. Candelaria Massal. 

Asci 8-spored. 

Spermatia acrogenous 5. Parmeliopsis Nyl. 

Spermatia pleurogenous. 

Apothecia superficial 6. Parmelia Ach. 

Apothecia lateral. 

Apothecia on upper surface 7. Cetraria Ach. 

Apothecia on lower surface 8. *Nephromopsis Miill.-Arg. 

XLVII. USNEACEAE 

This also is a familiar family of lichens, Usnea barbata the "bearded moss" 

being one of the first lichens noted and chronicled. Algal cells Protococcaceae. 

Structure radiate, the upright or pendulous habit characteristic of 

the family securing all-round illumination. Special adaptations of the cortex 

or of the internal tissues have been evolved to strengthen the thallus against 

the strains incidental to their habit of growth as they are attached in 

nearly all cases by one point only, by a special sheath, or by penetrating 

hold-fasts. 

Apothecia are superficial or marginal and sometimes shortly stalked ; 

spores are simple or variously septate. 

Ranialina and Usnea, the most numerous, are cosmopolitan genera; 

Alectoria inhabits northern or hilly regions. 

The genus Evernia, also cosmopolitan, represents a transition between 

foliose and fruticose types; the fronds of the two species, though strap- 

shaped and generally upright, are dorsiventral and stratose, the gonidia 

for the most part lying beneath one surface; the other (lower) surface is 

either white or very dark-coloured. Everniopsis, formed of thin branching 

strap-shaped fronds, 

A number of genera, TJiamnolia, Siphu/a, etc. are of podetia-like structure, 

generally growing in swards. Several of them have been classified with 

Cladoniae, but they lack the double thallus. One of these, Endocena, a 

is also dorsiventral. 

sterile monotypic Patagonian lichen, with stiff hollow coralloid fronds, was 

classified by Hue 1 

along with SipJiula\ recently 

he has transferred it to his 

family Polycaulionaceae 2 based on Polycauliona regale (Placodium frustu- ^ 

losnin Darbish.), and allied to Placodium Sect. T/iamnoma 3 . In recent studies 

Hue has laid most stress on thalline characters. He places the new family 

between "Ramalinaceae" and " Alectoriaceae." is Dactylinaarctica a common 

Arctic soil-lichen. 

1 Hue 1892. 

2 Hue 1914. 

3 Tuckerman 1872, p. 107. 

22 2

340 

Thallus strap- shaped. 

Structure dorsiventraL 

Greyish-green 

SYSTEMATIC 

above I. Evernia Ach. 

Whitish-yellow above 2. *Evemiopsis NyL 

Structure radiate alike on both surfaces. 

Fronds grey; medulla of loose hyphae 3. Ramalina Ach. 

Fronds yellow ; medulla traversed by strands 4. *Letharia A. Zahlbr. 

Thallus filamentous. 

Medulla a strong "chondroid" strand 5. Usnea DilL 

Medulla of loose hyphae. 

Spores simple 6. Alectoria Ach. 

Spores muriform, brown 7. *Oropogon Fr. 

Thallus of upright podetia-like fronds. 

Fronds rather long (about two inches), tapering,^ 8. Thamnolia Ach. (Cerania 

white I S. F. Gray). 

Fronds shorter, blunt 

Medulla solid 9. *Siphula Fr. 

Medulla partly or entirely hollow. 

Fronds swollen and tall (about two inches) 

Fronds coralloid, entangled 

Fronds short, upright 

XLVIII. CALOPLACACEAE 

10. *Dactylina NyL 

n. *Endocena Cromb. 

12. *Dufourea NyL 

In this family Zahlbruckner has included the squamulose or crustaceous 

lichens with colourless polarilocular spores, relegating those with more 

highly developed thallus or with brown spores to other families. He has 

also substituted the name Caloplaca for the older Placodium, the latter being, 

as he considers, less well defined. 

Algal cells are Protococcaceae. The thallus is mostly light-coloured, 

generally some shade of yellow, and, with few exceptions, contains parietin, 

which gives a purple colour on the application of potash. The squamulose 

forms are closely appressed to the substratum, and have often a definite 

rounded outline (effigurate). The spores have a thick median septum with 

a loculus at each end and a connecting canal 1 . 

In Blastenia the outer thalline margin is obscure or absent though 

gonidia are frequently present below the hymenium. Caloplacaceae occur 

all over the globe: they are among the most brilliantly coloured of all 

lichens. Polycauliona Hue 1 

possibly belongs here: though based on thalline 

rather than on spore characters, one species at least has polarilocular spores. 

Apothecia with a distinct thalline margin i. Caloplaca Th. Fr. 

Apothecia without a thalline margin 2. Blastenia Th. Fr. 

1 See p. 188. Hue 1908.


XLIX. TELQSCHISTACEAE 

PolariJocular colourless spores are the distinguishing feature of this 

family as of the Caloplacaceae. Algal cells Protococcaceae. The thallus 

of Teloschistaceae is more highly developed, being either foliose or fruticose, 

though never attaining to very large dimensions. The cortex of Xanthoria 

( foliose) is plectenchymatous, that of Teloschistes (fruticose) is fibrous. The 

species of both genera are yellow- or greenish-yellow due to the presence of 

the lichen-acid parietiru 

Both genera have a wide distribution over the globe, more especially in 

maritime regions. 

Thallus foliose i. Xanthoria Th. Fr. 

Thallus fruticose 2. Teloschistes Norm. 

L. B CELL!ACEAE 

A family of crustaceous lichens distinguished by the brown two-celled 

spores. Algal cells Protococcaceae. Zahlbruckner has included here Bufllia 

and Rinodina; the former with a distinctly lecideine fruit and with thinly 

septate spores; the latter lecanorine and with spores of the polarilocular 

type, with a very wide central septum pierced in most of the species by 

a canal which may or may not traverse the middle lamella of the wall. 

Rinodina is closely allied to Physciaceae, while Buellia has more affinity 

with Lecideaceae and is near to Rhizocarpon. 

Both genera are of world-wide distribution. 

Apothecia lecideine, without a thalline margin i. Buellia De Xot. 

Apothecia lecanorine, with a thalline margin 2. Rinodina MassaL 

LI. PHYSCIACEAE 

Thallus foliose or partly fruticose, and generally attached by rhizinae. 

Algal cells Protococcaceae. The spores resemble those of Rinodina, darkcoloured 

with a thick septum and reduced cell-lumina. As in that species 

there may be a second septum in each cell, giving a 3-septate spore; but 

that is rare. 

Pyxine, a tropical or subtropical genus, is lecanorine only in the very 

early stages; it soon loses the thalline margin. Anaptychia is differentiated 

from Physria by the subfruticose habit though the species are nearly all 

dorsiventral in structure, only a few of them being truly radiate and corticate 

on both surfaces. The upper cortex of Anaptychia is fibrous, but that 

character appears also in most species of Physcia either on the upper or the 

lower side. Physcia and Anaptychia are widely distributed. 

Thalline margin absent in apothecia 

Thalline margin present in apothecia. 

Thallus foliose 2. Physcia Schreb. 

I. *Pyxine XyL 

Thallus fruticose 3- Anaptychia Koerb.

342 

SYSTEMATIC 

C. *HYMENOLICHENS 

Fungus a Basidiomycete, akin to Thelephora. Algal cells Scytonema or 

Chroococcus. Thallus crustaceous, squamulose or foliose. Spores colourless, 

produced on basidia, on the under surface of the free thallus. 

The Hymenolichens 1 are few in number and are endemic in tropical 

or warm countries. They inhabit soil or trees. 

Thallus of extended lobes. 

Gonidia near the upper surface i. *Dictyonema Zahlbr. 

Gonidia in centre of tissue 2. *Cora Fr. 

Thallus squamulose, irregular 3. *Corella Wain. 

II. NUMBER AND DISTRIBUTION OF LICHENS 

i. ESTIMATES OF NUMBER 

Calculations have been made and published, once and again, as to the 

number of lichen species occurring over the globe or in definite areas. In 

1898 Fiinfstuck stated that about 20,000 different species had been described, 

but as many of them had been proved to be synonyms, and since many 

must rank as forms or varieties, the number of well-authenticated species 

did not then, according to his estimate, exceed 4000. Many additional 

genera and species have, however, been discovered since then. In Engler 

and Prantl's Pflanzenfamilien, over 50 families and nearly 300 genera find 

a place, but even in these larger groupings opinions differ as to the limits 

both of genera and families, and lichenologists would not all accept the 

arrangement given in that volume. 

Fiinfstuck has reckoned that of his estimated 4000, about 1500 are 

European and of these at least 1200 occur in Germany. Probably this is 

too low an estimate for that large country. Leighton in 1879 listed, in his 

British Lichen Flora, 1710 in all, and, as the compilation includes varieties, 

2 

it cannot be considered as very far astray. On comparing it with Olivier's 

recent statistics of lichens, we find that of the larger fruticose and foliose 

species, 310 are recognized by him for the whole of Europe, 206 of these 

occurring in the British Isles. Leighton's estimate of similar species is 

about 145, without including varieties now reckoned as good species. In 

a more circumscribed area, Th. Fries 3 described for Spitzbergen about 210 

different lichens, a number that closely approximates to the 206 recent re- 

cords by Darbishire 4 for the same area. 

A general idea of the comparative numbers of the different types of 

lichens may be gathered from Hue's compilation of exotic lichens 5 

, examined 

1 See 2 

p. 152. 

Olivier 1907. 

4 


5 Hue 1892. 

3 Th. Fries 1867.

NUMBER OF LICHENS 343 

or described by Nylander, and now in the Paris herbarium. There are 135 

genera with 3686 species. Of these, about 829 belong to the larger foliose 

and fruticose lichens (including Cladoniae)\ the remaining 2857 belong to 

the smaller kinds, most of them crustaceous. 

2. GEOGRAPHICAL DISTRIBUTION 

A. GENERAL SURVEY 

The larger foliose and fruticose lichens are now fairly well known and 

described for Europe, and the knowledge of lichens in other continents is 

gradually increasing. It is the smaller crustaceous forms that baffle the investigator. 

The distribution of all lichens over the surface of the earth is 

controlled by two principal factors, climate and substratum ; for although 

lichens as a rule require only support, they are most of them restricted to one 

or another particular substratum, either organic or inorganic. As organisms 

which develop slowly, they require an unchanging substratum, and as sun- 

plants they avoid deeply shaded woodlands: their occurrence thus depends 

to a large extent on the configuration and general vegetation of the country. 

Though so numerous and so widely distributed, lichens have not evolved 

that great variety of families and genera characteristic of the allied fungi 

and algae. They conform to a few leading types of structure, and thus the 

Orders and Families are comparatively few, and more or less universal. 

They are most of them undoubtedly very old plants and were probably 

wide-spread before continents and climates had attained their present 

stability. Arnold 1 indeed considers that a large part of the present-day 

lichens were almost certainly already evolved at the end of the Tertiary 

period, and that they originated in a warm or probably subtropical climate. 

As proof of this he cites such genera as Graphis, Thelotrenia and Arthonia* 

which are numerous in the tropics though rare in the colder European 

countries ; and he sees further proof in the fact that many fruticose and 

gelatinous lichens do not occur further north than the forest belt, though 

they are adapted to cold conditions. Several genera that are abundant in 

the tropics are represented outside these regions by only one or few species, 

as for instance Conotrenia urceolatum and Bonibyliospora incana. 

During the Ice age of the Quaternary period, not many new species can 

have arisen, and such forms as were not killed off must have been driven 

towards the south. As the ice retreated the valleys were again stocked with 

southern forms, and northern species were left behind on mountain tops all 

over the globe. 


2 These genera are associated with Trentepohlia algae which are numerous and abundant in 

tropical climates, and their presence there may possibly account for these particular lichens.

344 

SYSTEMATIC 

In examining therefore the distribution of lichens, it will be found that 

the distinction between different countries is relative, certain families being 

more or less abundant in some regions than others, but, in general, nearly 

all being represented. Certain species are universal, where similar conditions 

prevail. This is especially true of those species adapted to extreme cold, as 

that condition, normal in polar regions, recurs even on the equator if the 

mountains reach the limit of perpetual snow ; 

follows on the lines of the horizontal. 

the vertical distribution thus 

In all the temperate countries we find practically the same families, with 

some few exceptions; there is naturally more diversity of genera and species. 

Genera that are limited in locality consist, as a rule, of one or few species. 

In this category, however, are not included the tropical families or genera 

which may be very rich in species: these are adapted to extreme conditions 

of heat and often of moisture, and cannot exist outside tropical or subtropical 

regions, extreme heat being more restricted as to geographical position than 

extreme cold. 

In the study of distribution the question which arises as to the place of 

origin of such widely distributed plants is one that is difficult to solve. 

Wainio 1 has attempted the task in regard to Cladonia, one of the most 

unstable genera, the variations of form, which are dependent on external 

circumstances, being numerous and often bewildering. In his fine monograph 

of the genus, 132 species are described and 25 of these are cosmo- 

politan. 

The distribution of Phanerogams is connected, as Wainio points out, 

with causes anterior to the present geological era, but this cannot be the 

case in a genus so labile and probably so recent as Cladonia, though some 

of the species have existed long enough to spread and establish themselves 

from pole to pole. Endemic species, or those that are confined to a com- 

paratively limited area, are easily traced to their place of origin, that being 

generally the locality where they are found in most abundance, and as 

a general rule in the centre of that area, though there may be exceptions: 

a plant for instance that originated on a mountain would migrate only in 

one direction towards the regions of greater cold. 

The difficulty of determining the primitive. stations of cosmopolitan, or 

of widely spread, species is much greater, but generally they also may be 

referred to their area of greatest abundance. Thus a species may occur 

frequently in one continent and but rarely in another, even where the conditions 

of climate, etc., are largely comparable. It may therefore be inferred 

that the plant has not yet reached the full extent of possible distribution in 

the less frequented area. As examples of this, Wainio cites, among other 

instances, Cladonia papillaria, which has a very wide distribution in Europe, 

1 Wainio 1897.

DISTRIBUTION 345 

but, as yet, has been found only in the eastern parts of North America; and 

Cl. pycnodada, a plant which braves the climate of Cape Horn and the 

Falkland Islands, but has not travelled northward beyond temperate North 

America: the southern origin of that species is thus plainly indicated. Wainio 

also finds that evidence of the primitive locality of a very widely spread 

species may be obtained by observing the locality of species derived from 

it, which are as yet of limited distribution ; presumably these arose in the 

ancestral place of origin, though this indication is not always to be relied 

on. If, however, the ancestral plant has given rise to several of these rarer 

related species, those of them that are most closely allied to the primitive 

plant would be found near to it in the original locality. 

A detailed account of species distribution according to these indications 

is given by Wainio and is full of interest. No such attempt has been made 

to deal with any other group, and the distribution of genera and species can 

only be suggested. An exhaustive comparison of the lichens of different 

regions is beyond the purpose of our study and is indeed impossible as, 

except in some limited areas, or for certain species, the occurrence and distribution 

are not fully known. It is in any case only tentatively that genera 

or species can be described as local or rare, until diligent search has been 

made for them over a wider field. The study of lichens from a floristic point 

of view lags behind that of most other groups of plants. The larger lichen 

forms have received more attention,' as they are more evident and more 

easily collected ; but the more minute species are not easily detected, and, 

as they are largely inseparable from their substratum of rocks, or trees, etc., 

on which they grow, they are often difficult to collect. They are also in 

many instances so indefinite, or so alike in outward form, that they are 

liable to be overlooked, only a m'icroscopic examination revealing the differ- 

ences in fruit and vegetative structure. 

Though much remains to be done, still is enough known to make the 

of extreme interest. It will be 

geographical distribution of lichens a subject 

found most instructive to follow the usual lines of treatment, which give the 

three great divisions : the 

of the globe. 

Polar, the Temperate and the Tropical regions 

B. LICHENS OF POLAR REGIONS 

Strictly speaking, this section should include only lichens growing within 

the Polar Circles; but in practice the lichens of the whole of Greenland and 

those of Iceland are included in the Arctic series, as are those of Alaska: 

the latitudinal line of demarcation is not closely adhered to. With the 

northern lichens may also be considered those of the Antarctic continent, 

as well as those of the islands just outside the Antarctic Circle, the South

346 SYSTEMATIC 

Shetlands, South Orkneys, Tierra del Fuego, South Georgia and the Falkland 

Islands. During the Glacial period, the polar forms must have spread with 

the advancing cold ; as the snow and ice retreated, these forms have been 

left, as already stated, on the higher colder grounds, and representatives of 

polar species are thus to be found very far from their original haunts. There 

are few exclusively boreal genera: the same types occur at the Poles as in 

the higher subtemperate zones. One of the most definitely polar species, 

for instance, Usnea (Neuropogon] melaxantha grows in the whole Arctic zone, 

and, in the Antarctic, is more luxuriant than any other lichen, but it has also 

been recorded from the Andes in Chili, Bolivia and Peru, and from New 

Zealand (South Island). 

Cold winds are a great feature of both poles, and the lichens that by 

structure or habit can withstand these are the most numerous ; those that 

have a stout cortical layer are able to resist the low temperatures, or those 

that grow in tufts and thus secure mutual protection. In Arctic and Subarctic 

regions, 495 lichens have been recorded, most of them crustaceous. Among 

the larger forms the most frequently met are certain species of Peltigera, 

P armelia, Gyrophora, Cetraria, Cladonia, Stereocaulon and Alectoria. Among 

smaller species Lecanora tartarea spreads everywhere, especially over other 

vegetation, Lecanora varia reaches the farthest limits to which wood, on 

which it grows, has drifted, and several species of Placodium occur con- 

stantly, though not in such great abundance." Over the rocks spread also 

many crustaceous Lecideaceae too numerous to mention, one of the most 

striking being the cosmopolitan Rhizocarpon geographicnm. 

Wainio 1 has described the lichens collected by Almquist 

at Pitlekai in 

N.E. Siberia just on the borders of the Arctic Circle, and he gives a vivid 

account of the general topography. The snow lies on the ground till June 

and falls again in September, but many lichens succeed in growing and 

fruiting. It is a region of tundra and sand, strewn more or less with stones. 

Most of the sand is bare of all vegetation; but where mosses, etc., have 

gained a footing, there are also a fair number of lichens : Lecanora tartarea, 

Psoroma hypnorum, with Lecideae, Parmeliae, Cladoniae, Stereocaulon alpinnm, 

Solortna crocea, SpJiaeropJwrus globosus, Alectoria nigricans and Gyrophora 

proboscidea. Some granite rocks in that neighbourhood rise to a height of 

200 ft., and though bare of vegetation on the north side, yet, in sheltered 

nooks, several species are to be found. Stunted bushes of willow grow 

here and there, and on these occur always the same : species Placodium 

ferrugineum, Rinodina archaea, Buellia myriocarpa and Arthopyrenia punctiformis. 

Some species such as Sphaerophorus globosus, Dactylina arctica 

(a purely Arctic genus and species) and Thamnolia vermicularis are so. 

abundant that they bulk as largely as other better represented genera such 

1 Wainio 1909.


as Cladoniae, Lecanorae or Lecideae. 

areas. 

On the soil, Lecanorae cover the largest 

Wainio determined a large number of lichens with many new species, 

but the region is colder than that of Lappland, and trees with tree-lichens 

are absent, with the exception of those given above. In Arctic Siberia, 

Elenkin 1 

discovered a new lichen Placodium subfruticulosum which scarcely 

differs from Darbishire's 2 Antarctic species PI. fruticulosnm (or /-*. regale); 

both are distinguished by the fruticose growth of the thallus, for which reason 

Hue 3 

placed them in a new genus, Polycauliona. 

The Antarctic Zone and the neighbouring lands are less hospitable to 

plant life than the northern regions, and there is practically no accumulation 

of detritus. Collections have been made by explorers, and several lists have 

been published which include a marvellous number of species common to 

both Poles, if the subantarctic lands are included in the survey. An analytic 

study of the various lists has been published by Darbishire 4 . He recognizes 

1 06 true Antarctic lichens half of which are Arctic as well. The greater 

number are crustaceous and are plants common also to other lands though 

a certain number are endemic. The most abundant genera in species as 

well as individuals are Lecidea and Lecanora. Several bright yellow species 

of Placodium PI. elegans, PL murorum, etc., are there as at the North Pole. 

Among the larger forms, Parnieliae, Cetrariae, and Cladoniae are fairly 

numerous; Usneae and Rainalinae rather uncommon, while members of the 

Stictaceae are much more abundant than in the North. The common species 

of Peltigera also occur in Antarctica, though P. aphthosa and P. venosa are 

wanting ; both of these latter are boreal species. Darbishire adds that lichens 

have so great a capacity to withstand cold, that they are only checked by 

the snow covering, and were bare rocks to be found at the South Pole, he 

is sure lichens would take possession of them. The most southerly point 

at which any plant has been found is 78 South latitude and 162 East 

longitude, in which locality the lichen Lecanora subfusca was collected bymembers 

of Scott's Antarctic expedition (1901-1904) at a height of 5000 ft. 

A somewhat different view of the Antarctic lichen flora is indicated by 

Hue 3 in his account of the plants brought back by 

the second French 

Antarctic Expedition. The collection was an extremely favourable and 

blocks of stone with their communities of lichens were 

important one : great 

secured, and these blocks were entirely covered, the crustaceous species, 

especially, spreading over every inch of space. 

Hue determined 126 species, but as 15 of these came from the Magellan 

regions only 1 1 1 were truly Antarctic. Of these 90 are new species, 29 of 

them belonging to the genus Buellia. Hue considers, therefore, that in 

Antarctica there is a flora that, with the exception of cosmopolitan species, 

1 Elenkin 1906. 


3 Hue 1915. 

4 Darbishire 1912.

34 8 

SYSTEMATIC 

is different from every other, and is special to these southern regions. Dar- 

bishire himself described 34 new Antarctic species, but only 10 of these 

are from true Antarctica; the others were collected in South Georgia, the 

Falkland Islands or Tierra del Fuego. Even though many species are 

endemic in the south, the fact remains that a remarkable number of lichens 

which occur intermediately on mountain summits are common to both Polar 

areas. 

C. LICHENS OF THE TEMPERATE ZONES 

Regions outside the Polar Circles which enjoy, on the whole, cool moist 

climates, are specially favourable to lichen growth, and the recorded numbers 

are very large. The European countries are naturally those in which the 

lichen flora is best known. Whereas polar and high Alpine species are 

stunted in growth and often sterile, those in milder localities grow and fruit 

well, and the more highly developed species are more frequent. Parmeliae, 

Nephromae, Usneae and Ramalinae become prominent, especially in the 

more northern districts. Many Arctic plants are represented on the higher 

altitudes. A comparison has been made between the lichens of Greenland 

and those of Germany: of 286 species recorded for the former country, 213 

have been found in Germany, the largest number of species common to 

both countries being crustaceous. Lindsay 1 considered that Greenland 

lichens were even more akin to those of Scandinavia. 

There is an astonishing similarity of lichens in the Temperate Zone all 

round the world. Commenting on a list of Chicago lichens 2 

by Calkins , 

Hue 3 

pointed out that with the exception of a few endemic species they 

resemble those of Normandy. The same result appears in Bruce Fink's 4 

careful compilation of Minnesota lichens, which may be accepted as typical 

of the Eastern and Middle States of North Temperate America. The 

genera from that region number nearly 70, and only two of these, Omphalaria 

and Heppia, are absent from our British Flora. The species naturally present 

much greater diversity. Very few Graphideae are reported. In other States 

of North America there occurs the singular aquatic lichen, Hydrothyria 

venosa, nearly akin to Peltigera. 

If we contrast American lichens with these collected in South Siberia 

near Lake Baikal 5 

, we recognize there also the influence of temperate 

conditions. Several species of Usnea are listed, U. barbata, U. florida, 

U. hirta and U. longissima, all of them also American forms, U. longissima 

having been found in Wisconsin. Xanthoria parietina, an almost cosmo- 

politan lichen, is absent from this district, and is not recorded from Minnesota. 

The opinion 6 in America is that it is a maritime species: Tuckerman gives 

1 

2 

Lindsay 1870. 

Calkins 1896. 


3 * Hue 1898. 

Fink 1903. 

6 Comm. Heber Howe.


its habitat as "the neighbourhood of a great water," and reports it from 

near Lake Superior. In our country it grows at a good distance from the 

sea, in Yorkshire dales, etc., but all our counties would rank as maritime 

in the American sense. Lecanora tartarea which is rare in Minnesota is also 

absent from the Lake Baikal region. It occurs frequently both in Arctic 

and in Antarctic regions, and is probably also somewhat maritime in habitat. 

Many of the Parmeliae, NepJiromiae and Peltigerae, common to all northern 

temperate climes, are Siberian as are also Cladoniae and many crustaceous 

species. There is only one Sticta, St. Wrightii, a Japanese lichen, recorded 

by Wainio from this Siberian locality. 

A marked difference as regards species is noted between the Flora of 

Minnesota and that of California. Herre 1 has directed attention to the 

great similarity between the lichens of the latter state and those of 

: Europe many European species occur along the coast and nowhere else 

in America so far as is yet known as ; examples he cites, among others, 

Calicium hyperellum, Lecidea quernea, L. aromatica, Gyrophora polyrhiza, 

Pertusaria amara, Roccella fuciformis, R. fucoides and R. tinctoria. The 

Scandinavian lichen, Letharia vulpina, grows abundantly there and fruits 

freely; it is very rare in other parts of America. Herre found, however, 

no specimens of Cladonia rangiferina, Cl. alpestris or CL syhatica, nor 

any species of Graphis\ he is unable to explain these anomalies in distri- 

bution, but he considers that the cool equable climate is largely responsible: 

it is so much more like that of the milder countries of Europe than of the 

states east of the Sierra Nevada. His contention is supported by a con- 

sideration of Japanese lichens. With a somewhat similar climate there is 

a great preponderance of European forms. Out of 382 species determined 

by Nylander 2 

, 209 were European. There were 17 Graphideae, 31 Parmeliae, 

and 23 Cladoniae, all of the last named being European. These results of 

Nylander's accord well with a short list of 30 species from Japan compiled 

by Muller 3 at an earlier date. They were chiefly crustaceous tree-lichens; 

but the Cladoniae recorded are the familiar British species Cl. fimbriata, 

Cl. pyxidata and CL verticillata. 

With the Japanese Flora may be compared a list 4 of Maingay's lichens 

from China, 35 in all. Collema limosum, the only representative of Collemaceae 

in the list, is European, as are the two species of Ramalina, R.graci- 

lenta and R. pollinaria ; 

four species of Physcia are European, the remaining 

Ph. picta being a common tropical or subtropical plant. Lecanora saxicola, 

L. cinerea, Placodium callopismnm and PI. citrinum are cosmopolitan, other 

Lecanorae and most of the Lecideae are new. Graphis scripta, Opegrapka 

subsiderella and Arthonia cinnabarina the few Graphideae collected are 

1 Herre 1910. 


4 Nylander and Cromhie 1884. 

3 Muller 1879.

350 

SYSTEMATIC 

more or less familiar home plants. Among the Pyrenocarpei, Verrucaria 

(Pyrenuld) nitida occurs ; it is a widely distributed tree-lichen. 

It is unnecessary to describe in detail the British lichens. Some districts 

have been thoroughly worked, others have barely been touched. The flora 

as a whole is of a western European type showing the influence of the Gulf 

Stream, though there is also a representative boreal growth on the moorlands 

and higher hills, especially in Scotland. Such species as Parmelia pubescens, 

P. stygia and P. alpicola recall the Arctic Circle while Alectoriae, Cetrariae 

and Gyrophorae represent affinity with the colder temperate zone. 

In the southern counties such species as Sticta aurata, S. damaecornis, 

Phaeographis Lyellii and Lecanora (Lecanid) holophaea belong to the flora 

of the Atlantic seaboard, while in S.W. Ireland the tropical genera Leptogidium 

and Anthracothedum are each represented by a single species. The 

tropical or subtropical genus Coenogonium occurs in Great Britain and in 

Germany, with one sterile species, C. ebeneum. Enterographa crassa is 

another of our common western lichens which however has travelled east- 

wards as far as Wiesbaden. Roccella is essentially a maritime genus of 

warm climates : two species, R.fuaformtsand R.fucoides, grow on our south 

and west coasts. The famous R. tinctoria is a Mediterranean plant, though 

it is recorded also from a number of localities outside that region and has 

been collected in Australia. 

In the temperate zones of the southern hemisphere are situated the great 

narrowing projections of South Africa and South America with Australia and 

New Zealand. As we have seen, the Antarctic flora prevails more or less in 

the extreme southern part of America, and the similarity between the lichens 

of that country and those of New Zealand is very striking, especially in the 

fruticulose forms. There is a very abundant flora in the New Zealand 

islands with their cool moist climate and high mountains. Churchill 

Babington 1 described the collections made by Hooker. Stirton 2 added 

many species, among others Calycidium cuneatum, evidently endemic. Later, 

Nylander 3 

published the species already known, and Hellbom 4 followed 

with an account of New Zealand lichens based on Berggsen's collections ; 

many more must be still undiscovered. Especially noticeable as compared 

with the north, are the numbers of Stictaceae which reach their highest 

development of species and individuals in Australasia. They are as numerous 

and as prominent as are Gyrophoraceae in the north. A genus of Parmelia- 

ceae, Hetorodea, which, like the Stictae, bears cyphellae on the lower surface, 

is peculiar to Australia. 

A warm current from the tropical Pacific Ocean passes southwards along 

the East Coast of Australia, and Wilson 6 has traced its influence on the 

1 

Babington 1855. 

2 Stirton 1875. 

5 Wilson 1892. 

3 Nylander 1888. 4 Hellbom 1896.


lichens of Australia and Tasmania to which countries a few tropical species 

of Graphis, Chiodecton and Trypethelium have migrated. Various unusual 

types are to be found there also: the beautiful Cladonia retepora (Fig. 71), 

which spreads over the ground in cushion-like growths, with the genera 

Thysanothecium and Neophyllis, genera of Cladoniaceae endemic in these 

regions. 

The continent of Africa on the north and east is in so close connection 

with Europe and Asia that little peculiarity in the flora could be expected. 

In comparing small representative collections of lichens, 37 species from 

Egypt and 20 from Palestine, Miiller 1 found that there was a great affinity 

between these two countries. Of the Palestine species, eight were cosmo- 

politan ; among the crustaceous genera, Lecanorae were the most numerous. 

There was no record of new genera. 

The vast African continent more especially the central region has 

been but little explored in a lichenological sense; but in 1895 Stizenberger 2 

listed all of the species known, amounting to 1 593, and new plants and new 

records have been added since that day. The familiar genera are well 

represented, Nephromium, Xanthoria, Physcia, Parmelia, Ranialina and 

Roccella, some of them by large and handsome species. In the Sahara 

Steiner' found that genera with blue-green algae such as the Gloeolichens 

were particularly abundant ; 

Heppia and Endocarpon were also frequent. 

Algeria has a Mediterranean Flora rather than tropical or subtropical. 

Flagey 4 records no species of Graphis for the province of Constantine, and 

only 22 species of other Graphideae. Most of the 519 lichens listed by him 

there are crustaceous species. South America stretches from the Tropics 

in the north to Antarctica in the south. Tropical conditions prevail over 

the central countries and tropical tree-lichens, Graphidaceae.Thelotremaceae, 

further West, on the Pacific slopes, Usneae and Ramalinae 

etc. are frequent ; 

hang in great festoons from the branches, while the foliose Parmeliae and 

Stictae grow to a large size on the trunks of the trees. 

Wainio's 8 Lie/tens du Bresil is one of the classic systematic books and 

embodies the writer's views on lichen classification. There are no new 

families recorded though a number of genera and many species are new, 

and, so far as is yet known, these are endemic. Many of our common forms 

are absent thus ; Peltigera is represented by three species only, P. leptoderma, 

P. spuriella and P. Americana, the two latter being new species. Sticta 

(including Stictina) includes only five species, and Coenogonium three. There 

are 39 species of Parmelia with 33 of Lecanora and 68 of Lecidea, many of 

them new species. 

1 

Miiller- Argau 1884. 

4 

Flagey 1892. 

* 

Stizenberger 1888-1895. 


3 Steiner 1895.

352 

SYSTEMATIC 

D. LICHENS OF TROPICAL REGIONS 

In the tropics lichens come under the influence of many 

climates : on 

the high mountains there is a region of perpetual snow, lower down a gradual 

change to temperate and finally to tropical conditions of extreme heat, and, 

in some instances, extreme moisture. There is thus a bewildering variety 

of forms. By "tropical" however the warmer climate is always implied. 

Several families and genera seem to flourish best in these warm moist 

conditions and our familiar species grow there to a large size. Among 

crustaceous families Thelotremaceae and Graphidaceae are especially abun- 

dant, and probably originated there.. In the old comprehensive genus 

Graphis, 300 species were recorded from the tropics. It should be borne in 

mind that Trentepohlia, the alga that forms the gonidia of these lichens, is 

very abundant in the tropics. Coenogonium, a genus containing about twelve 

species and also associated with Trentepohlia, is scarcely found in Europe, 

except one sterile species, C. ebenenm. Other species of the genus have been 

recorded as far north as Algeria in the Eastern Hemisphere and Louisiana 

in the Western, while one species, C. implexum, occurs 

temperate zone in Australia and New Zealand. 

in the southern 

Of exclusively tropical lichens, the Hymenolichens are the most note- 

worthy. They include three genera, Cora, Corella and Dictyonema, the few 

species of which grow on trees or on the ground both in eastern and western 

tropical countries. 

Other tropical or subtropical forms are Oropogon loxensis, similar to 

Alectoria in form and habit, but with one brown muriform spore in the 

ascus; it is only found in tropical or subtropical lands. Physcidia Wrightii 

(Parmeliaceae) is exclusively a Cuban lichen. Several small genera of 

Pyrenopsidaceae such asjenmania (British Guiana), Paulia (Polynesia) and 

Phloeopeccania (South Arabia) seem to be confined to very hot localities. 

On the other hand Collemaceae are rare : Wainio records from Brazil only 

four species of Collema, with nine of Leptogium. 

Among Pyrenolichens, Paratheliaceae, Mycoporaceae and Astrotheliaceae 

are almost exclusively of tropical distribution, and finally the leaf 

lichens with very few exceptions. These follow the leaf algae, Mycoidea, 

Phycopeltis, etc., which are so abundant on the coriaceous long-lived green 

leaves of a number of tropical Phanerogams. All the Strigulaceae are 

epiphytic lichens. Phyllophthalmaria (Thelotremaceae) is also a leaf genus; 

one of the species, Ph. coccinea, has beautiful carmine-red apothecia. The 

genera of the tropical family Ectolechiaceae also inhabit leaves, but they 

are associated with Protococcaceae ; one of the genera Sporopodium 1 is re- 

markable as having hymenial gonidia. Though tropical in the main, 

1 Wainio 1890, II. p. 27 (recorded under Lecided).


epiphyllous lichens may spread to the regions beyond: Sforopodium 

Caucasium and a sterile Strigula were found by Elenkin and Woronichin 1 

on leaves of Buxus sempervirens in the Caucasus, well outside the tropics. 

Pilocarpon, an epiphytic genus, is associated with Protococcaceae ; one 

of the species, P. leucoblepharum, spreads from the bark to the leaves of pinetrees 

; it is widely distributed and has also been reported in the Caucasus". 

Ckrysothrix, in which the gonidia belong to the algal genus Pa/mella, grows on 

Cactus spines in Chili, and may also rank as a subtropical epiphyllous lichen. 

A series of lichens from the warm temperate region of Transcaucasia 

investigated by Steiner 3 were found to be very similar to those of Central 

Europe. Lecanoraceae were, however, more abundant than Lecideaceae 

and Verrucariaceae were comparatively rare. 

Much of Asia lies within tropical or subtropical influences. Several 

regions have received some amount of attention from collectors. From 

4 

Persia there has been published a list of 59 species determined by Miiller ; 

several of them are Egyptian or Arabian 1 

plants, 5 are new species, but the 

greater number are European. 

A small collection of 53 species from India, near to Calcutta, published 

by Nylander 5 

included a new , genus of Caliciaceae, Pyrgidium (P. bengalense), 

allied to Sphinctrina. He also recorded Ramalina angulosa in African species, 

along with R. calicaris, R. farinacea and Parmelia perlata, f. isidiophora, 

which are British. Other foliose forms, Physcia picta, Pyxine Cocoes and 

with these were collected 

P. Meissnerii are tropical or subtropical ; along 

crustaceous tropical species belonging to Lecanorae, Lecideae, Graphideae, etc. 

Leighton 6 

published a collection of Ceylon lichens and found that Gra- 

phideae predominated. Nylander 7 came to the same conclusion with regard 

to lichens referred to him: out of 159 species investigated from Ceylon, 

there were 36 species of Graphideae. In another list 8 of Labuan, Singapore 

and Malacca lichens, 164 in all, he found that 56 belonged to the Graphidei, 

36 to Pyrenocarpei, 14 to Thelotremei and n to Parmelei; only 15 species 

were European. 

On the whole it is safe to conclude from the above and other publications 

that the exceptional conditions of the tropics have produced many distinc- 

tive lichens, but that a greater abundance both of species and individuals is 

now to be found in temperate and cold climates. 

III. FOSSIL LICHENS 

In pronouncing on the great antiquity of lichens, proof has been adduced 

from physiological rather than from phytogeological 

evidence. It would 

have been of surpassing interest to trace back these plants through the ages, 

1 2 Elenkin and Woronichin 1908. Jaczewski 

5 6 



3 4 

1904. 

Steiner 1919. 

MUller 1891. 

' 

8 

Nylander 1900. Nylander 1891. 

s. L. 

2 3

354 

SYSTEMATIC 

even if it were never possible to assign to any definite period the first 

symbiosis of the fungus and alga ; but among fossil plants there are only 

scanty records of lichens and even these few are of doubtful determination. 

The reason for this is fairly obvious : not only are the primitive thalline 

forms too indistinct for recognizable preservation, but all lichens are characterized 

by the gelatinous nature of the hyphal or of the algal membranes 

which readily imbibe water. They thus become soft and flaccid and unfit 

to leave any impress on sedimentary rocks. It has also been pointed out by 

Schimper 1 

that while deciduous leaves with fungi on them are abundant in 

fossil beds, lichens are entirely wanting. These latter are so firmly attached 

to the rock's or trees on which they grow that they are rarely dislodged, and 

form no part of wind- or autumn-fall. Trunks and branches of trees lose 

their bark by decay long before they become fossilized and thus all trace of 

their lichen covering disappears. 

The few records that have been made are here tabulated in chronological 

order: 

1. PALAEOZOIC. Schimper decides that there are no records of lichens 

in the earlier epochs. Any allusions 2 to their occurrence are held to be ex- 

tremely vague and speculative. 

2. MESOZOIC. Braun 3 has recorded a Ramalinites lacerns from the 

Keuper sandstone at Eckersdorf, though later 4 he seemed to be doubtful as 

to his determination. One other lichen, an Opegrapha, has been described 5 

from the chalk at Aix. 

3. CAINOZOIC. In the brown-coal formations of Saxony Engelhardt 6 

tertiaria, a much branched plant, the fronds 

finds two lichens : Ramalina 

being flat and not channelled " and of further interest that it is attached to 

a carbonized stem." The second form, Lichen dichotomies, has a dichoto- 

mously branching strap-shaped frond. " There is sufficient evidence that 

these fronds were cylindrical and that the width is due to pressure. In one 

place a channel is visible, filled with an ochraceous yellow substance." 

Other records on brown coal or lignite are : Verrncarites geanthricis" 1 

Goepp., somewhat similar to Pyrenida nitida, found at Muskau in Silesia ; 

Opegrapha Thomasiana* Goepp., near to Opegrapha varm,a.nd Graphis scripta 

9 succinea Goepp. on a piece of lignite in amber beds, all of them doubtful. 

10 

Schimper has questioned, as he well might, Ludwig's records from 

lignite from the Rhein-VVetterau Tertiary formations ; these are : Cladonia 

rosea, Lichen albineus, L. diffissus and L. orbiculatus ; he thinks they 

are probably fungus mycelia. Another lichen, a Parmelia with apothecia, 

1 

Schimper 1869, p. 145. 

2 

Lindsay 1879. 

:i Braun 1840. 

* Muenster 1846, p. 26. 

5 

Eltingshausen and Debey 1857. 

6 

Engelhardt 1870 (PI. I. figs, i and 2). 

7 

Goeppert 1845, p. 195. 

8 

See Schimper 1869, pp. 145, etc. 

"Goeppert and Menge 1883, t. i, fig. 3. 

10 

Ludwig 1859, p. 61 (t. 9, figs. 1-4), 1859-61.

FOSSIL LICHENS 355 

which recalls somewhat P. saxatilis or P. conspersa, collected by Geyler 

also in the brown coal of Wetterau is accepted by Schimper 1 as more trust- 

worthy. 

More authentic also are the lichens from the amber beds of Konigsberg 

and elsewhere collected by Goeppert and others. These deposits are 

Cainozoic and have been described by Goeppert and Menge 2 as middle 

Miocene. Schimper gives the list as: Parmelia lacnnosa Meng. and Goepp., 

fragments of thallus near to P. saxatilis; Sphaerophornscoralloides; Cladonia 

divaricata Meng. and Goepp.; Cl. furcata; Ramalina calicaris \zrs.fraxinea 

and canaliculata ; 

Cornicularia aculeata, C. subpubescens Goepp., C, ochroleiica, 

C. succinea Goepp., and Usnea barbata var. hirta. Schimper rather deprecates 

specific determinations when dealing with such imperfect fragments. 

In a later work Goeppert and Menge 2 state that they have found twelve 

different amber lichens and that among these are Physcia ciliaris, Parmelia 

physodes and Graphis (probably G. scripta succinea) along with Peziza retinae 

which is more generally classified among lichens as Lecidea (Biatorelld} 

resinae. 

Another series of lichens found in recent deposits in North Europe has 

been described by Sernander 3 as "subfossil." While engaged on the investi- 

gations undertaken by the Swedish Turf-Moor Commission, he noted the 

alternation of slightly raised Sphagnum beds with lower-lying stretches of 

Calluna and lichen moor in some instances dense communities of Cladonia 

rangiferina. In time the turf-forming Sphagnum overtopped and invaded 

the drier moorland, covering it with a new formation of turf. Beneath these 

" 

layers of regenerated turf" were found local accumulations of blackened 

remains of the Cladonia still recognizable by the form and branching. Some 

specimens of Cetraria islandica were also determined. 

Of especial lichenological interest in these northern regions was the 

Calcareous Tufa or Calc-sinter in which Sernander also found subfossil 

lichens distinct impressions of Peltigera spp. and the foveolae of endolithic 

calcicolous species. 

In another category he has placed Ramalina fraxinea, Graphis sp. and 

Opegrapha sp., traces of which were embedded with drift in the Tufa. In 

the two Graphideae the walls of apothecia and pycnidia were preserved. 

Sernander considers their presence of interest as testifying to warmer con- 

ditions than now prevail in these latitudes. 

' 

Schimper in Zittel 1890. 

2 

Goeppert and Menge 1883. 

3 Sernander 1918. 

232

CHAPTER IX 

ECOLOGY 

A. GENERAL INTRODUCTION 

ECOLOGY is the science that deals with the habitats of plants and their 

response to the environment of climate or of substratum. Ecology in the 

lichen kingdom is habitat "writ large," and though it will not be possible in 

so wide a field to enter into much detail, even a short examination of lichens 

in this aspect should yield interesting results, especially as lichens have 

never, at any time, been described without reference to their habitat. In 

very early days, medicinal Usneas were supposed to possess peculiar virtues 

according to the trees on which they grew and which are therefore carefully 

recorded, and all down the pages of lichen literature, no diagnosis has been 

drawn up without definite reference to the nature of the substratum. Not 

only rocks and trees are recorded, but the kind of rock and the kind of tree 

are often specified. The important part played by rock lichens in preparing 

soil for other plants has also received much attention 1 . 

Several comprehensive works on Ecology have been published in recent 

times and though they deal mainly with the higher vegetation, the general 

to lichens. A series of definitions 

plan of study of land plants is well adapted 

and explanations of the terms used will be of service : 

Thus in a work by Moss 2 we read " The flora is composed 

of the indi- 

vidual species: the vegetation comprises the groupings of these species into 

ensembles termed vegetation units or plant communities." And again : 

1. "A plant formation is the whole of the vegetation which occurs on 

a definite and essentially uniform habitat." All kinds of plants are included 

in the formation, so that strictly speaking a lichen formation is one in which 

lichens are the dominant plants. Cf. p. 394. The term however is very loosely 

used in the literature. A uniform habitat, as regards lichens, would be that 

of the different kinds of soil, of rock, of tree, etc. 

2. "A. plant association is of lower rank than a formation, and is charac- 

terized by minor differences within the generally uniform habitat." It 

represents a more limited community within the formation. 

" 

3. A plant society is of lower rank than an association, and is marked 

by still less fundamental differences of the habitat." The last-named term 

represents chiefly aggregations of single species. Moss adds that: ''plant 

community is a convenient and general term used for a any 

vegetation unit of 

rank." 

Climatic conditions and geographical position are included in any con- 

sideration of habitat, as lichens like other plants are susceptible to external 

influences. 

1 See p. 392. 

2 Moss 1913.

GENERAL INTRODUCTION 357 

Ecological plant-geography has been well defined by Macmillan 1 as 

"the science which treats of the reciprocal relation between physiographic 

conditions and life requirements of organisms in so far as such relations 

manifest themselves in choice of habitats and method of establishment 

upon them... resulting in the origin and development of plant formations." 

B. EXTERNAL INFLUENCES 

The climatic factors most favourable to lichen development are direct 

light (already discussed) 2 

a moderate or cold , 

temperature, constant moisture 

and a clear pure atmosphere. Wind also affects their growth. 

a. TEMPERATURE. Lichens, as we have seen, can endure the heat of 

direct sunlight owing to the protection afforded by thickened cortices, colour 

pigments, etc. Where such heat is so intense as to be injurious the gonidia 

succumb first :i 

. 

Lichens endure low temperatures better than other plants, their xerophytic 

structure rendering them proof against extreme conditions: the hyphae 

have thick walls with reduced cell lumen and extremely meagre contents. 

Freezing for prolonged periods does them little injury ; they revive again 

when conditions become more favourable. Efficient protection is also afforded 

by the thickened cortex of such lichens as exist in Polar areas, or at high 

altitudes. Thus various species of Cetrariae with a stout "decomposed" 

amorphous cortex can withstand very low temperatures and grow freely on the 

tundra, while Cladonia rangiferina, also a northern lichen, but without a continuous 

cortex, cannot exist in such cold conditions, unless in localities where 

it is protected by a covering of snow during 

the most inclement seasons. 

b. HUMIDITY. A high degree of humidity is distinctly of advantage to 

the growth of the lichen thallus, though when the moist conditions are ex- 

cessive the plants become turgid and soredial states are developed. 

The great abundance of lichens in the western districts of the British 

Isles, where the rainfall is heaviest, is proof enough of the advantage of 

moisture, and on trees it is the side exposed to wind and rain that is most 

plentifully covered. A series of observations on lichens and rainfall were 

made by West 4 and have been published since his death. He has remarked 

in more than one of his papers that a most favourable situation for lichen 

growth is one that is subject to a drive of wind with much rain. In localities 

with an average of 216 days of rain in the year, he found abundant and 

luxuriant growths of the larger foliose species. In West Ireland there were 

specimens oiRicasolia laetevirens measuring 1 65 by 60 cm. I n West Scotland 

with an "average of total days of rain, 225," he found plants of Ricasolia am- 

plissima 150 x 90 cm. in size, of R. laetevirens 120x90 cm., while Pertusaria 

1 Macmillan 1894. 

- See p. 240 et seq. 

3 See p. 238. 

4 West 1915-

358 

ECOLOGY 

globulifera formed a continuous crust on the trees as much as 120 x 90 cm. 

Lecanora tartarea seemed to thrive exceptionally well when subject to 

driving mists and rains from mountain or moorland, and was in these circumstances 

frequently the dominant epiphyte. Bruce Fink 1 

also observed 

in his ecological excursions that the number of species and individuals was 

greater near lakes or rivers. 

Though a fair number of lichens are adapted to life wholly or partly 

under water, land forms are mostly xerophytic in structure, and die off if 

submerged for any length of time. The Peltigerae are perhaps the most 

hydrophilous of purely land species. Many Alpine or Polar forms are 

covered with snow for long periods. In the extreme north it affords more 

or less protection; and Kihlman 2 and others have remarked on the scarcity 

of lichens in localities denuded of the snow mantle and exposed to severe 

winter cold. On the other hand lichens on the high Alpine summits that are 

covered with snow the greater part of the year suffer, according to Nilson 3 

, 

from the excessive moisture and the deprivation of light. Foliose and 

fruticose forms were, he found, dwarfed in size; the crustaceous species had 

a very thin thallus and in all of them the colour was impure. Gyrophorae 

seemed to be most affected : folds and outgrowths of the thallus were formed 

and the internal tissues were partly disintegrated. Lichens on the blocks 

of the glacier moraines which are subject to inundations of ice-cold water 

after the snow has melted, were unhealthy looking, poorly developed and 

often sterile, though able to persist in a barren state. Lindsay 4 noted as 

a result of such conditions on Cladoniae not only sterility but also de-. 

formity both of vegetative and reproductive organs ; discolouration and 

mottling of the thallus and an increased development of squamules of the 

primary thallus and on the podetia. 

c. WIND. Horizontal crustaceous or foliose lichens are not liable to 

direct injury by wind as their close adherence to the substratum sufficiently 

shelters them. It is only when the wind carries with it any considerable 

quantity of sand that the tree or rock surfaces are swept bare and prevented 

from ever harbouring any vegetation, and also, as has been already noted, 

the terrible winds round the poles are fatal to lichens exposed to the 

blasts unless they are provided with a special protective cortex. After 

crustaceous forms, species of Cetraria, Stereocaulon and Cladonia are best 

fitted for weathering wind storms: the tufted 5 cushion-like growth adopted 

by these lichens gives them mutual protection, not only against wind, but 

against superincumbent masses of snow. Kihlman 2 has given us a vivid 

account of wind action in the Tundra region. He noted numerous hollows 

completely scooped 

out down to the sand : in these sheltered nooks he 

1 2 Fink 1894. 

Kihlman 1890. 

4 

Lindsay 1869. 

6 Sattler 1914. 

3 Nilson 1907.

EXTERNAL INFLUENCES 359 

observed the gradual colonization of the depressions, first by a growth of 

hepatics and mosses and by such ground lichens as Peltigera canina, P. 

aphthosa and Nephromium arcticum ; they cover the soil and in time the 

hollow becomes filled with a mass of vegetation consisting of Cladonias, 

mosses, etc. On reaching a certain more exposed level these begin to wither 

and die off at the tips, killed by the high cold winds. Then arrives Lecanora 

tartarea, one of the commonest Arctic lichens, and one which is readily 

a saprophyte on decayed vegetation. It covers completely the mound of 

weakened plants which are thus smothered and finally killed. The collapse 

of the substratum entails in turn the breaking of the Lecanora crust, and 

the next high wind sweeps away the whole crumbling mass. How long 

recolonization takes, it was impossible to find out. 

Upright fruticose lichens are necessarily more liable to damage by wind, 

but maritime Ramalinae and Roccellae do not seem to suffer in temperate 

climates, though in regions of extreme cold fruticose forms are dwarfed and 

stunted. The highest development of filamentous lichens is to be found in 

more or less sheltered woods, but the effect of wind on these lichens is not 

wholly unfavourable. Observations have been made by Peirce 1 on two 

American pendulous lichens which are dependent on wind for dissemina- 

tion. On the Californian coasts a very large and very frequent species, 

Ramalina reticulata (Fig. 64), is seldom found undamaged by wind. In 

Northern California the deciduous oaks Quercus alba and Q. Douglasii are 

festooned with the lichen, while the evergreen " live oak," Q. chrysolepis, 

with persistent foliage, only bears scraps that have been blown on to it. 

Nearer the coast and southward the lichen grows on all kinds of trees and 

shrubs. The fronds of this Ramalina form a delicate reticulation and when 

moist are easily torn. In the winter season, when the leaves are off the 

trees, wind- and rain-storms are frequent ; the lichen is then exposed to 

the full force of the elements and fragments and shreds are blown to other 

trees, becoming coiled and entangled round the naked branches and barky 

excrescences, on which they continue to grow and fruit perfectly well. 

A succeeding storm may loosen them and carry them still further. Peirce 

noted that only plants developed from the spore formed hold-fasts and 

they were always small, the largest formed measuring seven inches in length. 

Both the hold-fast and the primary stalk were too slight to resist the tearing 

action of the wind. 

Schrenk 2 made a series of observations and experiments 

with the lichens 

Usneaplicata and U. dasypoga, long hanging forms common on short-leaved 

conifers such as spruce and juniper. The branches of these trees are often 

covered with tangled masses of the lichens not due to local growth, but to 

wind-borne strands and to coiling and intertwining of the filaments owing 


2 Schrenk 1898.

360 

to successive wetting and drying. 

ECOLOGY 

Tests were made as to the force of wind 

required to tear the lichens and it was found that velocities of 77 miles per 

hour were not sufficient to cause any pieces of the lichen to fly off when it 

was dry; but after soaking in water, the first pieces were torn off at 50 miles 

an hour. These figures are, however, considered by Schrenk to be too high 

as it was found impossible in artificially created wind to keep up the condi- 

tion of saturation. It is the combination of wind and rain that is so effective 

in ensuring the dispersal of both these lichens. 

d. HUMAX AGENCY. Though lichens are generally associated with undisturbed 

areas and undisturbed conditions, yet accidents or convulsions of 

nature, as well as changes effected by man, may at times prove favourable 

to their development. The opening up of forests by thinning or clearing 

will be followed in time by a growth of tree and ground forms; newly 

planted trees may furnish a new lichen flora, and the building of houses 

and walls with their intermixture of calcareous mortar will attract a par- 

ticular series of siliceous or of lime-loving lichens. A few lichens are partial 

to the trees of cultivated areas, such as park-lands, avenues or road-sides. 

Among these are several species of Physcia : Ph. pulverulenta, Ph. ciliaris 

and Ph. stellaris, some species of Placodinm, and those lichens such as 

Lecanora varia that frequently grow on old palings. 

On the other hand lichens are driven away from areas of dense population, 

or from regions affected by the contaminated air of industrial centres. 

In our older British Floras there are records of lichens collected in London 

during the eighteenth century in Hyde Park and on these have long disappeared. 

Hampstead Heath but 

A variety of Lecanora galactina seems to be 

the only lichen left within the London district : it has been found at Camden 

Town, Netting Hill and South Kensington. 

So recently as 1866, Nylander 1 made a list of the lichens growing in the 

Luxembourg gardens in Paris; the chestnuts in the alley of the Observatory 

were the most thickly covered, and the list includes about 35 different 

species or varieties, some of them poorly developed and occurring but rarely, 

others always sterile, but quite a number in healthy fruiting condition. All 

of them were crustaceous or squamulose forms except Parmelia acetabulum, 

which was very rare and sterile; Physcia obscura var. and Ph. pulverulenta 

var., also sterile; Physcia stellaris with occasional abortive apothecia and 

Xantlwria parietina, abundant and fertile. In 1898, Hue 2 tells us, there 

were no lichens to be found on the trees and only traces of lichen growth 

on the stone balustrades. 

The question of atmospheric pollution in manufacturing districts and its 

effect on vegetation, more especially on lichen vegetation, has received 

special attention from Wheldon and Wilson 1 in their account of the lichens of 

1 


* Hue 1898. 

* Wheldon and Wilson 1915.

EXTERNAL INFLUENCES 361 

South Lancashire, a district peculiarly suitable for such an inquiry,as nowhere, 

according to the observations, are the evil effects of impure air so evident 

or so wide-spread. The unfavourable conditions have prevailed for a long 

time and the lichens have consequently become very rare, those that still 

survive leading but a meagre existence. The chief impurity is coal smoke 

which is produced not only from factories but from private dwellings, and 

its harmful effect goes far beyond the limits of the towns or suburbs, lichens 

being seen to deteriorate as soon as there is the slightest deposition of coal 

combustion products especially sulphur compounds either on the plants 

or on the surfaces on which they grow. The larger foliose and fruticose 

forms have evidently been the most severely affected. "While genera of 

bark-loving lichens such as Calicimn, Usnea, Ramalina, Grapliis, Opegrapha, 

Arthonia etc. are either wholly absent or are poorly represented in the 

district," corticolous species now represent about 15 per cent, of those that 

are left; those that seem best to resist the pernicious influences of the smoky 

atmosphere are, principally, Lecanora varia, Parmelia saxatilis,P.pJiysodes and 

to a less degree P. sulcata, P.fuliginusa var. laetevirens and Pcrtusaria ainara. 

Saxicolous lichens have also suffered severely in South Lancashire; not 

only the number of species, but the number of individuals is enormously 

reduced and the specimens that have persisted are usually poorly developed. 

The smoke-producing towns are situated in thevalley-bottoms.andthe smoke 

rises and drifts on to the surrounding hills and moorlands. The authors 

noted that crustaceous rock-lichens were in better condition on horizontal 

surfaces such as the copings of walls, or half-buried stones, etc. than on the 

perpendicular or sloping faces of rocks or walls. This was probably due 

to what they observed as to the effect of water trickling down the inclined 

substrata and becoming charged with acid from the rock surfaces. They 

also observed further that a calcareous substratum seemed to counteract the 

effect of the smoke, the sulphuric acid combining with the lime to form 

calcium sulphate, and the surface-washings thus being neutralized, the 

lichens there are more favourably situated. They found in good fruiting 

condition, on mortar, cement or concrete, the species Lecanora urbana, 

L. campestris, L. crenulata, Verrncaria mitralis, V. rupestris, Thelidinin 

microcarpum and StaurotJiele hymenogonia. Some of these occurred on the 

mortar of sandstone walls close to the town, "whilst on the surface of the 

sandstone itself no lichens were present." 

Soil-lichens were also strongly affected, the Cladoniae of the moorlands 

being in a very depauperate condition, and there was no trace of Stereocanlon 

or of Sphatropliorns species, which, according to older records, previously 

occurred on the high uplands. 

The influence of human agency is well exemplified in one of the London 

districts In 1883 Crombie published a list of the lichens recorded from

362 

ECOLOGY 

Epping Forest during the nineteenth century. They numbered 171 species, 

varieties or forms, but, at the date of publication, many had died out owing 

to the destruction of the older trees ; the undue crowding of the trees that 

were left and the ever increasing population on the outskirts of the Forest. 

Crombie himself made a systematic search for those that remained, and 

could only find some 85 different kinds, many of them in a fragmentary or 

sterile condition. 

R. Paulson and P. Thompson 1 commenced a lichen exploration of the 

Forest 27 years after Crombie's report was published, and they have found 

that though the houses and the population have continued to increase round 

the area, the lichens have not suffered. " 

Species considered by Crombie as 

rare or sterile are now fairly abundant, and produce numerous apothecia. 

Such are Baeomyces rufus, B. roseus, Cladonia pyxidata, Cl. macilenta var. 

coronata, Cl. Floerkeana f. trachypoda, Lecanora varia, Lecidea decolorant and 

Lecidea tricolor? They conclude that "some at least of the Forest lichens 

are in a far more healthy and fertile condition than they were 27 years ago." 

They attribute the improvement mainly to the thinning of trees and the 

opening up of glades through the Forest, letting in light and air not only to 

the tree trunks but to the soil. In 191 2 2 the authors in a second paper 

reported that 109 different kinds had been determined, and these, though 

still falling far short of the older lichen flora, considerably exceed the list 

of 85 recorded in 1883. 

C. LICHEN COMMUNITIES 

Lichen communities fall into a few definite groups, though, as we shall 

see, not a few species may be found to occur in several groups species 

that have been designated by some workers as "wanderers." The leading 

communities are : 

1. ARBOREAL, including those that grow on leaves, bark or wood. 

2. TERRICOLOUS, ground-lichens. 

3. 

SAXICOLOUS, rock-lichens. 

4. OMNICOLOUS, lichens that can exist on the most varied substrata, such 

as bones, leather, iron, etc. 

conditions the 

5. LOCALIZED COMMUNITIES in which owing to special 

lichens may become permanent and dominant. 

In all the groups lichens are more or less abundant. In arboreal and 

terricolous formations they may be associated with other plants; in saxi- 

colous and omnicolous formations they are the dominant vegetation. It will 

be desirable to select only a few of the typical communities that have been 

observed and recorded by workers in various lands. 

1 Paulson and Thompson 191 1. 

* Paulson and Thompson 1917.

LICHEN COMMUNITIES 363 

I. ARBOREAL 

Arboreal communities may be held to comprise those lichens that grow 

on wood, bark or leaves. They are usually the dominant and often the sole 

vegetation, but in some localities there may be a considerable development 

of mosses, etc., or a mantle of protococcaceous algae may cover the bark. 

Certain lichens that are normally corticolous may also be found on dead 

wood or may be erratic on neighbouring rocks : Usnea florida 

for instance 

is a true corticolous species, but it grows occasionally on rocks or boulders 

generally in crowded association with other foliose or fruticose lichens. 

Most of the larger lichens are arboreal, though there are many exceptions 

: Parmelia perlata develops to a large size on boulders as well as on 

trees ; some species of Ramalinae are constantly saxicolous while there are 

only rare instances of Roccellae that grow on trees. The purely tropical or 

subtropical genera are corticolous rather than saxicolous, but species that 

have appeared in colder regions may have acquired the saxicolous habit : 

thus Coenogonium in the tropics grows on trees, but the European species, 

C. ebeneum, grows on stone. 

a. EPIPHYLLOUS. These grow on Ferns or on the coriaceous leaves of 

evergreens in the tropics. Many of them are associated with Phycopeltis, 

Phyllactidium or Mycoidea, and follow in the wake of these algae. Observations 

are lacking as to the associations or societies of these lichens whether 

they grow singly or in companies. The best known are the Strigulaceae : 

there are six genera in that family, and some of the species have a wide 

distribution. The most frequent genus is Strigula associated with Phycopeltis 

which forms round grey spots on leaves, and is almost entirely confined 

to tropical regions. Chodat 1 records a sterile species, 5. Buxi, on box leaves 

from the neighbourhood of Geneva. 

Other genera, such as those of Ectolechiaceae, which inhabit fern scales 

and evergreen leaves, are associated with Protococcaceae. Pilocarpon leuco- 

It is 

blepharum with similar gonidia grows round the base of pine-needles. 

found in the Caucasus. In our own woods, along the outer edges, the lower 

spreading branches of the fir-trees are often decked with numerous plants 

of Parmelia physodes, a true " 

plant society," but that lichen is a confirmed 

"wanderer." Biatorina Bouteillei, on box leaves, is a British and Continental 

lichen. 

b. CORTICOLOUS. In this series are to be found many varying groups, 

the type of lichen depending more on the physical nature of the bark than 

on the kind of trees. Those with a smooth bark such as hazel, beech, lime, 

etc., and younger trees in general, bear only crustaceous species, many of 

them with a very thin thallus, often partly immersed below the surface. 

1 Chodat 1912.

364 

ECOLOGY 

As the trees become older and the bark takes on a more rugged character, 

other types of lichens gain a foothold, such as the thicker crustaceous forms 

like Pertusaria, or the larger foliose and fruticose species. The moisture that 

is collected and retained by the rough bark is probably the important factor 

in the establishment of the thicker crusts, and, as regards the larger lichens, 

both rhizinae and hold-fasts are able to gain a secure grip of the broken-up 

unequal surface, such as would be quite impossible on trees with smooth bark. 

Among the first t6 pay attention to the ecological grouping of corticolous 

lichens was A. L. Fee 1 

a Professor of Natural Science and an , 

Army doctor, 

who wrote on many literary and botanical subjects. In his account of the 

Cryptogams that grow on "officinal bark," he states that the most lichenized 

of all the Cimhotiae was the one known as " Loxa," the bark of which was 

covered with species of Parmelta, Sticta and Usnea along with crustaceous 

forms of Lecanora, Lecidea, Graphis and Verrucaria. Another species, Cin- 

chona cordifolia, was completely covered, but with crustaceous forms only : 

species of Graphidaceae, Lecanora and Lecidea were abundant, but Trypethelium, 

Chiodecton, Pyrenula and Verrucaria were also represented. On each 

species of tree some particular lichen was generally dominant: 

A species of Thelotrema on Cinchona oblongifolia. 

A species of Chiodecton on C. cordifolia. 

A species of Sarcographa on C. condaminea. 

Fries 2 

in his , geography of lichens, distinguished as arboreal and "hypophloeodal" 

species of Verrucariaceae, while the Graphideae, which also grew 

on bark, were erumpent. Usnea barbata, Evernia prunastri, etc., though grow- 

ing normally on trees might, he says, be associated with rock species. 

More extensive studies of habitat were made by Krempelhuber 3 in his 

Bavarian Lichens. In summing up the various "formations" of lichens, he 

gives lists of those that grow, in that district, exclusively on either coniferous 

or deciduous trees, with added lists of those that grow on either type of tree 

indifferently. Among those found always on conifers or on coniferous wood 

are : Letharia vulpina, Cetraria Laureri, Pannelia aleurites and a number of 

crustaceous species. Those that are restricted to the trunks and branches of 

leafy trees are crustaceous with the exception of some foliose Collemaceae 

such as Leptogium Hildenbrandii, Collema nigrescens, etc. 

Arnold 4 carried to its furthest limit the method of arranging lichens 

ecologically, in his account of those plants from the neighbourhood of 

Munich. He gives " formation " 

lists, not only for particular substrata and 

in special situations, but he recapitulates the species that he found on the 

several different trees. It is not possible to reproduce such a detailed survey, 

which indeed only emphasizes the fact that the physical characters of the 

bark are the most important factors in lichen ecology: that on smooth bark, 

1 Fee 1824. 

2 Fries 1831. 

3 

Krempelhuber 1861. 

4 Arnold 1891, etc.


whether of young trees, or on bark that never becomes really rugged, there 

is a preponderance of species with a semi-immersed thallus, and very 

generally of those that are associated with Trentepohlia gonidia, such as 

Graphidaceae or Pyrenulaceae, though certain species of Lecidea, Lecanora 

and others also prefer the smooth substratum. 

Bruce Fink 1 has published a series of important papers on lichen com- 

munities in America, some of them similar to what we should find in the 

British Isles. 

On trees with smooth bark he records in the Minnesota district: 

Xanthoria polycarpa. 

Candelaria concolor. 

Parmelia olivacea, P. adglutinata. 

Placodium cerinum. 

Lecanora subfusca. 

Bacidia fusca-rubella. 

Lecidea enteroleuca. 

Graphis scripta. 

Arlhonia lecideella, A. dispersa. 

Arthopyrenia punctiformis, A.fallax. 

Pyrenula nitida, P. thelena, P. cinerella, P. leucoplaca. 

On rough 

bark he records : 

Ramalina calicaris, R. fraxinea, R . fastigiata. 

Teloschistes chrysophthalmus. 

Xanthoria polycarpa, X. lychnea. 

Candelaria concolor. 

Parmelia perforata, P. crinita, P. Borreri, P. tiliacea, P. saxatilis, P. caperata. 

Physcia granulifera, Ph. pul-verulenta, Ph. stellaris, Ph. tnbacia, Ph. obscura. 

Collema pycnocarpum, C. flaccidum. 

Leptogium mycochroum. 

Placodium aurantiacum, PL cerinum. 

Lecanora subfusca. 

Perlusaria leioplaca, P. velata. 

Bacidia rubella, B . fuscorubella. 

Leddea enteroleuca. 

Rhizocarpon alboatrum, Buellia parasema. 

Opegrapha varia. 

Graphis scrip ta. 

Arthonia lecideella, A. radiata. 

A>'thopyrenia quinqueseplata, A. macrospora. 

Pyrenula nitida, P. leucoplaca. 

Finally, as generally representative 

of the commonest lichens in our 

woods of deciduous trees, including both smooth- and rough-barked, the community 

of oak-hazel woods as observed by Watson2 in Somerset maybequoted: 

Collema flaccidum. 

Calicium hyperellutn. 

i Fink 1902. 

* Watson 1909.

366 

ECOLOGY 

Ramalina calicaris, R. fraxinea with var. ampliata, R. fastigiata, R. farinacea and 

R. pollinaria. 

Parmelia saxatilis and f. furfuracea, P. caperata, P. physodes. 

Physcia pulverulenta, Ph. tenella (hispida). 

Lecanora subfusca, L. rugosa. 

Pertusaria amara, P. globulifera, P, communis, P. Wuljenii. 

Lecidea (Buellia} canescens. 

Graphis scripta. 

And on the soil of these woods : 

Cladonia pyxidata, Cl. pungens, Cl. macilenta, Cl, pityrea, Cl. squamosa and Cl. 

sylvatica. 

Paulson 1 

, from his observations of lichens in Hertfordshire, has concluded 

that the presence or absence of lichens on trees is influenced to a considerable 

degree by the nature of the soil. They were more abundant in woods 

on light well-drained soils than on similar communities of trees on heavier soils, 

though the shade in the former was slightly more dense and therefore less 

favourable to their development; the cause of this connection is not known. 

c. LlGNICOLOUS. Lichens frequenting the branches of trees do not long 

continue when these have fallen to the ground. This may be due to the 

lack of light and air, but Bouly de Lesdain 2 has suggested that the chemical 

reactions produced by the decomposition of the bast fibres are fatal to them, 

Lecidea parasema alone continuing to grow and even existing for some time 

on the detached shreds of bark. 

On worked wood, such as old doors or old palings, light and air are well 

provided and there is often an abundant growth of lichens, many of which 

seem to prefer that substratum : the fibres of the wood loosened by weathering 

retain moisture and yield some nutriment to the lichen hyphae which burrow 

among them. Though a number of lichens grow willingly on dead wood, 

there are probably none that are wholly restricted to such a habitat. A few, 

such as the species of Coniocybe, are generally to be found on dead roots of 

trees or creeping loosely over dead twigs. They are shade lichens and fond 

of moisture. 

The species on palings or " dead wood communities " 

to us in our country are : 

Usnea hirta. Rinodina exigua. 

most familiar 

Cetraria diffusa. Lecanora ffagent, L. varia and its allies. 

Evernia furfuracea. 

Lecidea osfreata, L. parasema. 

Parmelia scortia, P. physodes. Buellia myriocarpa. 

Xanlhoria parietina. 


Cladoniaceae and Caliciaceae (several species). 

These may be found in very varying association. It has indeed been 

remarked that the dominant plant may be simply -the one that has first 

1 Paulson 19 r9- 

2 Lesdain 1912.


gained a footing, though the larger and more vigorous lichens tend to crowd 

out the others. Bruce Fink 1 has recorded associations in Minnesota : 

On wood : 

Teloschistes chrysophthalmus. 


Buellia parasema (disciformis\ B. turgescens. 

Calicium parietinum. 

Lecanora Hagem, L. varia. Thelocarpon prasinellum. 

Rinodina sophodes, R. exigua. 

On rotten stumps and : prostrate logs Peltigera 

canina. Cladonia fim- 

briata var. tubaeformis, Cl. gracilis, Cl. verticillata. CL symphicarpia, Cl. 

macilenta, Cl. cristatella. 

Except for one or two species such as Buellia turgescens, Cladonia sym- 

phicarpia, etc., the associations could be easy paralleled in our own country, 

though with us Peltigera canina, Cladonia gracilis and Cl. verticillata are 

ground forms. 

2. TERRICOLOUS 

In this community other vegetation is dominant, lichens are subsidiary. 

In certain conditions, as on heaths, they gain a permanent footing, in others 

they are temporary denizens and are easily crowded out. As they are 

generally in close contact with the ground they are peculiarly dependent 

on the nature of the soil and the water content. There are several distinct 

substrata to be considered each with its characteristic flora. Cultivated soil 

and grass lands need scarcely be included, as in the former the processes of 

cultivation are too harassing for lichen growth, and only on the more permament 

somewhat damp mossy meadows do we get such a species as Peltigera 

canina in abundance. Some of the earth-lichens are among the quickest 

growers : the apothecia of Baeomyces rosens appear and disappear within a 

year. Thrombium epigaeum develops in half a year; Thelidium mtnutulum 

in cultures grew from spore to 2 

spore, according to Stahl in three , 

months. 

There are three principal types of soil composition: (i) that in which 

there is more or less of lime; (2) soils in which silica in some form or other 

predominates, and (3) soils which contain an appreciable amount of humus. 

Communities restricted to certain soils such as sand-dunes, etc., are 

treated separately. 

a. ON CALCAREOUS SOIL. Any admixture of lime in the soil, either as 

chalk, limy clay or shell sand is at once reflected in the character of the 

lichen flora. On calcareous soil we may look for any of the squamulose 

Lecanorae or Lecideae that are terricolous species, such as Lecanora crassa, 

L. lentigera, Placodium fulgens, Lecidea lurida and L. decipiens. There are 

also the many lichens that grow on mortar or on the accumulated debris 

mixed with lime in the crevices of walls, such as Biatorina coeruleonigricans, 

species of Placodium, several species of Collema and of Verrucariaceae. 

1 Fink 1896, etc. 

3 Stahl 1877.

368 

ECOLOGY 

Bruce Fink 1 found in N.W. Minnesota an association on exposed cal- 

careous earth as follows : 

Heppia Despreauxii. 

Urceolaria scruposa. 

Biatora (Lecidea} decipiens. 

Biatora (Bacidia] muscorum. 

Dermatocarpon hepaticum. 

of a hill that was washed 

This particular 

association occupied the slope 

by lime-impregnated water. It was normally a dry habitat and the lichens 

were distinguished by small closely adnate thalli. 

There are more lichens confined to limy than to sandy soil. Arnold'2 

gives a list of those he observed near Munich on the former habitat : 

Cladonia sylvatica f. alpestris. Urceolaria scruposa f. argillacea. 

Cladonia squamosa f. subsquamosa. Verrucatia (Thrombium) epigaea. 

Lecidea decipiens. 

Cladonia rangiformis f. foliosa. 

Cladonia cariosa and f. sympkicarpa. Dermatocarpon cinereum. 

Peltigera canina f. soreumatica. Collema granulatum. 

Solorina spongiosa. 

Collema tenax. 

Heppia virescens. Leptogium byssinum. 

Lecanora crassa. 

It is interesting to note how many of these lichens specialized 

habitat are forms of species that grow in other situations. 

as to 

b. ON SILICEOUS SOIL. Lichens are not generally denizens of cultivated 

soil ; a few settle on clay or on sand-banks. Cladonia fimbriata and Cl. 

pyxidata grow frequently in such situations ; 

sandy or gravelly soil are, in the British Isles : 

others more or less confined to 

Baeomyces roseus. Gongylia -viridis. 

Baeomyces rufus. Dermatocarpon lachneum. 

Baeomyces placophyllus. Dermatocarpon hepaticum. 

Endocarpon spp. Dermatocarpon cinereum. 

These very generally grow in extended societies of one species only. 

In his enumeration of soil-lichens Arnold 2 

gives 40 species that grow on 

siliceous soil, as against 57 on calcareous. Many of them occurred on both. 

Those around Munich on siliceous soil only were : 

Cladonia cocci/era. Baeomyces rufus. 

Cladonia agaridformis. 

Secoliga (Gyalecta) bryophaga. 

Ler.idea gelatinosa. 

Psorotichia lutophila. 

Mayfield 3 in his account of the Boulder Clay lichen flora of Suffolk found 

only four species that attained to full development on banks and hedgerows. 

These were: Collema pidposum, Cladonia pyxidata, Cl. furcata var. corymbosa 

and Peltigera polydactyla. 

1 Fink 1902, etc. 


s Mayfield 1916.


On bare heaths of gravelly soil in Epping Forest Paulson and Thompson 1 

describe an association of such lichens as : 

Baeotnyces roseus. Cladonia macilenta. 

Baeomyces rufus. 

Cladonia furcata. 

Pycnothelia papillaria. 

Cetraria aculeata. 

Cladonia coccifera. Peltigera spuria. 

Leeidea granulosa. 

And on flints in the soil : Lecidca crustnlata and Rhizocarpon confer- 

voides. They found that Peltigera spuria colonized very quickly the burnt 

patches of earth which are of frequent occurrence in Epping Forest, while 

on wet sandy heaths amongst heather they found associated Cladonia syl- 

vatica f. tennis and Cl. finibriata subsp. y^w/

370 

ECOLOGY 

Cladonia cocci/era. Peltigera malacea. 

Cladonia pyxidata. . 

Peltigera 

canina. 

Cladonia fimbriata. Peltigera aphthosa. 

e. ON PEATY SOIL. Peat is generally found in most abundance in 

northern and upland regions, and is characteristic of mountain and moor- 

land, though there are great moss-lands, barely above sea-level, even in our 

own country. Such soil is of an acid nature and attracts a special type of 

plant life. The lichens form no inconsiderable part of the flora, the most 

frequent species being members of the Cladoniaceae. 

The principal crustaceous species on bare peaty soil in the British Isles 

are Lecidea uliginosa and L.granulosa. The former is not easily distinguishable 

from the soil as both thallus and apothecia are brownish black. The 

latter, which is often associated with it, has a lighter coloured thallus and 

apothecia that change from brick-red to dark brown or black ; Wheldon 

and Wilson 1 remarked that after the burning of the heath it was the first 

vegetation to appear and covered large spaces with its grey thallus. Another 

peat species is Icuiadophila ericetorum, but it prefers damper localities 

the two Lecideae. 

than 

To quote again from Arnold 2 : 24 species 

were found on turf around 

Munich, 13 of which were Cladoniae, but only four species could be considered 

as exclusively peat-lichens. These were: 

Cladonia Floerkeana. Thelocarpon turficolum. 

Biatora terricola. Geisleria sychnogonioides. 

The last is a very rare lichen in Central Europe and is generally found 

on sandy soil. Arnold considered that near Munich, for various reasons, 

there was a very poor representation of turf-lichens. 

f. ON MOSSES. Very many lichens grow along with or over mosses, 

either on the ground, 'on rocks or on the bark of trees, doubtless owing to 

the moisture accumulated and retained by these plants. Besides Cladoniae 

the commonest " moss " 

species in the British Isles are Bilimbia sabulosa, 

Bacidia muscormn, Rinodina Conradi, Lecidea sanguineoatra, Pannaria 

brunnea, Psoroma hypnorum and Lecanora tartarea, with species of Collema 

and Leptogium and Diploschistes bryopJiilus. 

Wheldon and Wilson 3 have listed the lichens that they found in Perth- 

shire on subalpine heath lands, on the ground, or on banks amongst mosses: 

Leptogrum spp. 

Lecidea granulesa. Peltigera spp. 

Lecidea uliginosa. 

Cetraria spp. 

Lecidea neglecta. 

Parmelia physodes. 

Bilimbia sabulosa. 

Psoroma hypnorum. 

Bilimbia ligniaria. 

Lecanora epibryon. 

Bilimbia melaena. 

Lecanora tartarea. Baeomyces spp. 

Lecidea coarctata. Cladonia spp. 

1 Wheldon and Wilson 1907. 

2 Arnold 1892, p. 34. 

s Wheldon and Wilson 1915.


As already described Lecanora tartarea* spreads freely over the mosses 

of the tundra. Aigret 2 in a study of Cladoniae notes that Cl. pyxidata, var. 

neglecta chooses little cushions of acrocarpous mosses, which are particularly 

well adapted to retain water. CL digitata, CLflabelliformis and some others 

grow on the mosses which cover old logs or the bases of trees. 

g. ON FUNGI. Some of the fungi, such as Polyporei, are long lived, and 

of hard texture. On species of Lensitcs in Lorraine, Kieffer 3 has recorded 

15 different forms, but they are such as naturally grow on wood and can 

scarcely rank as a separate association. 

3. 

SAXICOLOUS 

Lichens are the dominant plants of this v and the following formations, 

they alone being able to live on bare rock ; only when there has been formed 

a nidus of soil can other plants become established. 

a. CHARACTERS OF MINERAL SUBSTRATA. It has been often observed 

that lichens are influenced not only by the chemical composition of the 

rocks on which they grow but also by the physical structure. Rocks that 

weather quickly are almost entirely bare of lichens : the 

breaking up of the 

surface giving no time for the formation either of thallus or fruit. Close- 

grained rocks such as quartzite have also a poor lichen flora, the rooting 

hyphae being unable to penetrate and catch hold. Other factors, such as 

incidence of light, and proximity of water, are of importance in determining 

the nature of the flora, even where the rocks are of similar formation. 

b. COLONIZATION ON ROCKS. When a rock surface is laid bare it 

becomes covered in time with lichens, and quite fresh surfaces are taken 

number of species is 

possession of preferably to weathered surfaces 4 . The 

largest at first and the kind of lichen depends on the flora existing in the 

for instance, has stated that Lichen candelarius 

near neighbourhood. Link 5 

, 

was the first lichen to appear on the rocks he observed, and, if trees were 

growing near, then Lichen parietinus and Lichen tenellus followed soon after. 

After a time the lichens change, the more slow-growing being crowded out 

by the more vigorous. Crustaceous 8 

species, according to Malinowski , are 

most subject to this struggle for existence, and certain types from the nature 

of their thallus are more easily displaced than others. Those with a deeply 

cracked areolated thallus become disintegrated in the older central areas by 

repeated swelling and contracting of the areolae as they change from wet 

to dry conditions. Particles of the thallus are thus easily dislodged, and 

bare places are left, which in time are colonized again by the same lichen 

or by some invading species. There may result a bewildering 

1 See p. 358. 

8 Link 1795. 

2 

Aigret 1901. 

8 Kieffer 1894. 

Malinowski 1911. 

mosaic of 

4 Stahlecker 1906. 

242

37 2 ECOLOGY 

different thalli and fruits mingling together. Some forms such as Rhizo- 

carpum geographicum which have a very close firm thallus do not break away. 

In the course of time lichen communities come and go, and the plants of 

one locality may be different from those of another for no apparent reason. 

The question of colonization 1 was studied by Bruce Fink 2 on a "riprap" 

wall of quartz, 30 years old, built to protect and brace a railway in Iowa. 

Nearby was a grass swamp which supplied moisture especially to the lower 

end of the wall. A few boulders were present in the vicinity, but the nearest 

lichen "society" was on trees about 150 metres away and these bore corticolous 

Parmelias, Physcias, Ramalinas,Placodiums, Lecanoras and Rinodines 

which were only very sparingly represented on the riprap. Moisture-loving 

species never gained a footing; the extreme xerophytic conditions were 

evidenced by the character of the lichens, Biatora myriocarpoides (Lecidea 

sylvicola) occupying the driest parts of the wall. Lower down where more 

moisture prevailed Bacidia inundata and Stereocaulon paschale were the 

dominant species. Some 30 species or forms were listed of which 1 1 were 

Cladonias that grew mainly on debris from the disintegration of the wall. 

With the exception of two or three species the number of individuals was 

very small. 

Some of these lichens had doubtless come from the boulders, others from 

the trees ; the Cladonias were all known to occur within a few miles, but 

most of the species had been wind-borne from some distance. The Stereo- 

caulon present did not exist elsewhere in Iowa ; it had evidently been 

brought by the railroad cars, possibly on telegraph poles. 

A similar wall on the south side of the railway, subject to even more 

xerophytic conditions but with less disintegration of the surface, had a larger 

number of individuals though fewer species. Only one Cladonia and one 

Parmelia had gained a footing, the rest were crustaceous, Buellia myriocarpa 

being one of the most frequent. 

There are two types of rock of extreme importance in lichen ecology: 

those mainly composed of lime (calcareous), and those in which silica or 

silicates preponderate (siliceous). They give foothold to two corresponding 

groups of lichen communities, calcicolous and silicicolous. 

c. CALCICOLOUS. The pioneer in this section of lichen ecology is 

H. F. Link, who was a Professor of Natural Science and Botany at Rostock, 

then at Breslau, and finally in Berlin. He 3 

published in 1789, while still at 

Rostock, an account of limestone plants in his neighbourhood, most of them 

being lichens. In a later work he continues his Botanical Geography or 

" 

Geology " and gives more precise details as to the plants, some of which 

are essentially calcicolous though many of them he records also on siliceous 

rocks. 


2 Fink 1904. 

3 Link 1789.


Most calcicolous lichens are almost completely dependent on the lime 

substratum which evidently supplies some constituent that has become 

necessary to their healthy growth. Calcareous rocks are usually of softer 

texture than those mainly composed of silica, and not only the rhizoidal 

hyphae but the whole thallus both hyphae and gonidia may be deeply 

embedded. Only the fruits are visible and they are, in some species, lodged 

in tiny depressions (foveolae) scooped out of the surface by the lichen-acids 

acting on the easily dissolved lime. 

Those obligate lime species may be found in associations on almost any 

calcareous rock. Watson 1 

has given us a list of species that inhabit carboni- 

ferous limestone in Britain. Wheldon and Wilson 2 have described in West 

Lancashire the "grey calcareous rocks blotched with black patches of Pan- 

narias (Placynthium nigruni) and Verrucarias, or dark gelatinous rosettes of 

Collemas. White and grey Lecanorae and Verrucariae spread extensively, 

some of them deeply pitting the surface. These more sombre or colourless 

species are enlivened by an intermixture of orange-yellow Physciae (XantJioriae) 

and Placodii by the ochrey films of Lecanora ochracea and lemonyellow 

Q{ Lecanora xantholyta. Amongst the greenish scaly crusts of Lecanora 

crassa may be seen the bluish cushions of Lecidca coeruleo-nigricans, the 

whole forming an exquisite blend of tints." 

The flora recorded by Flagey 3 on the cretaceous rocks of Algeria in the 

Province of Constantine does not greatly differ, some of the species being 

identical with those of our own country. Placodiums and Rinodinas were 

abundant, as also Lecanora calcarea, Acarospora percaenoides and Urceolaria 

actinostoma var. calcarea. Also a few Lecideae along with Verrucaria 

lecideoides, V. fuscella, V. calciseda and Rndocarpon monstrosum. The rocks 

of that region are sometimes so covered with lichens that the stone is no 

longer visible. 

Bruce Fink 4 

gives a typical community on limestone bluffs in Minnesota: 

Pannaria (Placynthiuni) nigra. 

Crocynia lanuginosa. 

Omphalaria pulvinata. 

Collema plicatile. 

Collema pustulatum. 

Leptogium laceriim. 

Placodium citrinnm. 

Bacidia inundata. 

Rhizocarpon alboatrum var. 

Dennatocarpon miniatum. 

Staurothele itmbrinum. 

Forssell 5 

pointed out an interesting selective quality in the Gloeolichens 

which are associated with the gelatinous algae, Chroococcns, Gloeocapsa and 

Xanthocapsa. The genera containing the two former grow on siliceous rocks 

with the exception of Synalissa. The genera Omphalaria, Peccania, Anema, 

Psorotichia and Enchylium, in which Xanthocapsa is the gonidium, grow on 

1 2 2 3 

Watson . iQiS Wheldon and Wilson 1-907. 

Flagey i9Ot. 

4 2 8 

Bruce Fink ios . 

Forssell 1885.

374 

ECOLOGY 

calcareous rocks. Collemopsidinm is the only Xanthocapsa associate that is 

silicicolous. 

d. SILICICOLOUS. There is greater variety in the mineral composition 

and in the nature of the surface in siliceous than in calcareous rocks ; they are 

also more durable and give support to a large number of slow-growing forms. 

Silicon enters into the composition of many different types, from the 

oldest volcanic to the most recent of sedimentary rocks. Some of these are 

of hard unyielding surface on which only a few lichens are able to attach 

themselves. Such a rock is instanced by Servit 1 as occurring in Bohemia, 

and is known as Lydite or Lydian stone, a black flinty jasper. The associa- 

tion of lichens on this smooth rock was almost entirely Acarospora chloro- 

phana and Rinodina oreina, which as we shall see occur again as a "desert" 

association in Nevada; these two lichens grow equally well in sun or shade, 

and either sheltered or exposed as regards wind and rain. Acarospora chloro- 

phana, according to 

2 

Malinowski , arrives among the first on rocks newly 

laid bare, and forms large societies, though in time it gives place to Lecanora 

glaucoma (L. sordida}, a common silicicolous lichen. 

A difference has been pointed out by Bachmann 3 between the lichens 

of acid and of basic rocks. The acid series, such as quartz- and graniteporphyry, 

contain 70 per cent, and more of oxide of silica; the basic diabase 

and basalt not nearly 50 per cent. He observed that Rhizocarpon geographicum 

was the most frequent lichen of the acid porphyry, while on basalt there 

were only small scattered patches. Pertusaria corallina was abundant only 

on granitic rocks. On the other hand Pertusaria lactea f. cinerascens, DiploscJiistes 

scruposus, D. bryophilus and Buellia leptodine preferred the basic sub- 

stratum of diabase and basalt. In this case it is the chemical rather than the 

physical character of the rocks that affects the lichen flora, as porphyry and 

basalt are both close-grained, and are outwardly alike except in colouration. 

Other rocks, such as granite, in which the different crystals, quartz, mica 

and felspar are of varying hardness, are favourite habitats as affording not 

only durability but a certain openness to the rhizoidal hyphae, though in 

Shetland, West 4 found the granitic rocks bare owing to their too rapid 

weathering. In these rocks the softer basic constituents such as the mica are 

colonized first; the quartz remains a long time naked, though in time it 

also is covered. Wheldon and Wilson 5 

point out that the sandstone near to 

intrusive igneous rocks has become close-grained and indurated and bears 

Lecanora squamulosa, L. picea, Lecidea rivulosa and Rhizocarpon petraeum, 

which were not seen on the unaltered sandstone. It was also observed by 

Stahlecker 6 

, that, in layered rocks, the lichen chose the surface at right 

angles to the layering as the hyphae thus gain an easier entrance. 

1 Servit 1910. 

2 Malinowski 1911. 

Wheldon and Wilson 1913. 


6 Stahlecker 1906. 

4 West 1912.


It will only be possible to give a few typical associations from the many 

that have been published. Crustaceous forms are the most abundant. 

On granite and on quartzite not disintegrated Malinowski 1 

listed : 

Acarospora chlorophana. 

Lecidea tumida. 

Lecanora glaucoma. Biatorella sporostatia. 

Rhizocarpon mridiatrum. Biatorella testudinea. 

On granite and : 

quartzite disintegrated 

Aspicilia cinerea. 

Aspicilia gibbosa. 

Aspicilia tenebrosa. 

Buellia coracina. 

Catillaria (Biatorina) Hochstetteri. 

Rhizocarpon petraeum. 

Rhizocarpon geographicum vars. 

Biatorella cinerea. 

Lecanora badia. 

Lecanora ccnisia. 

Lecidea confluens. 

Lecideaf uscoatra. 

Lecidea platycarpa. 

Lecidea lapicida. 

Hacmiitonnna ventosum. 

On these disintegrated rocks there is a constant struggle for existence 

between the various species ; the victorious association finally consists of 

Lecanora badia, L. cenisia and Lecidea confluens with occasional growths of 

the following species : 

Aspicilia cinerea. Biatorella cinerea. 

Haematonnna -ventosum. Lecidea platycarpa. 

Rhizocarpon geographicum vars. 

A number of rock associations have been tabulated by Wheldon and 

Wilson 2 for Perthshire. Among others they give some of the most typical 

lichens on granitic and eruptive rocks : 

Sphaerophorus coralloides. Gyrophoraftocculosa. 

Sphaerophorits fragilis. Lecanora gelida. 

Platysma Fahlunense. Lecanora atra. 

Platysma commixtum. Lecanora badia. 

Platysma glaucnm. 

Lecanora far/area. 

Platysma lacunosum. 

Lecanora parella. 

Parmelia saxatilis. 

Lecanora ventosa. 

Parmelia omphalodes. 

Lecanora Dicksonii. 

Parmelia Mougeotii. 

Lecanora cinerea. 

Parmelia stygia. 

Lecanora peliocyplia. 

Parmelia tristis. 

Pertitsaria dealbata. 

Parmelia Ianata. 

Stereocaulon Delisei. 

Gyrophora proboscidea. 

Gyrophora cylindrica. 

Gyrophora torrefacta. 

Gyrophora polyphylla. 

Stereocaulon evolution. 

Stereocaulon coralloides. 

Stereocaulon denudatum. 

Psorotichia lugubris. 

Lecidea insercna. 

Lecidea panaeola. 

Lecidea contigna. 

Lecidca confluens. 

Lecidca lapicida. 

Lecidea plana. 

Lecidea mesotropa. 

Lecidea auriculata. 

Lecidea didncens. 

Lecidea aglaea. 

Lecidea rhntlosa. 

Lecidea Kochiana. 

Lecidea pycnocarpa. 

Buellia atrata. 

On siliceous rocks in West Lancashire the same authors 3 

Rhisocarpon Oederi. 

depict the 

lichen flora as follows: "There are many grey Parmcliae and Cladoniae 

1 Malinowski 1911. 


3 Wheldon and Wilson 1907.

37 6 

ECOLOGY 

with coral-like Sphaerophorei on the rocks, and on the walls smoky-looking 

patches of Parmelia fuliginosa and ragged fringes of Platysma glaucum and 

Evernia furfuracea. On the higher scars, flat topped tabular blocks exhibit 

black scaly Gyrophoreae, dingy green Lecidea (Rhizocarpon) viridiatra and 

mouse-coloured L. rivulosa. Suborbicular (whitish) patches of Pertusaria 

lactea and P. dealbata enliven the general sadness of tone, and everywhere 

loose rocks and stones are covered with the greyish-black spotted thallus 

of Lecidea contigua." 

On the Silurian series of rocks in the same district they describe a 

somewhat brighter coloured flora: "First Stereocaulons invite attention, 

and greenish or yellowish shades are introduced by an abundance of Lecanora 

sulphured, L. polytropa, Rhizocarpon geographicmn and Parmelia conspersa, 

often beautifully commingled with grey species such as Lecidea contigua 

and L. stellulata, and reddish angular patches of Lecanora Dicksonii. Also 

an abundance of orbicular patches of Haematomma ventosum with its 

reddish-brown apothecia." A brightly coloured association on the cretaceous 

sand-rocks of Saxon Switzerland has been described as "Sulphur lichens." 

These have recently 1 been determined as chiefly Lepraria chlorina, in less 

abundance Lecidea lucida and Calicium arenarium, with occasional growths 

of Coniocybe furfiiracea and Calicium corynellum. 

4. 

OMNICOLOUS LICHENS 

Some account must be taken in any ecological survey of those lichens 

that are indifferent to substrata. Certain species have become so adapted to 

some special habitat that they never or rarely wander ; others, on the con- 

trary, are true vagabonds in the lichen kingdom and settle on any substance 

that affords a foothold : on leather, bones, iron, pottery, etc. There can be 

no sustenance drawn from these supports, or at most extremely little, and 

it is interesting to note in this connection that while some rock-lichens are 

changed to a rusty-red colour by the infiltration of iron often from a 

water medium containing iron-salts those that live directly on iron are 

unaffected. 

The " wanderers " are more or less the same in every locality and they 

pass easily from one support to another. Bouly de Lesdain 2 made a tabulation 

of such as he found growing on varied substances on the dunes round 

Dunkirk and they well represent these omnicolous communities. It is in 

such a no man's land that one would expect to find an accumulation of 

derelict materials, not only favourably exposed to light and moisture, but 

undisturbed for long periods and bordering on normal lichen associations 

of soil, tree and stones. Arnold 3 also noted many of these peculiar habitats. 

1 Schade 1916. 


3 Arnold 1858.


The following were noted by Lesdain and other workers : 

On iron Xanthoria parietina, Physcia obscura and var. virella, Ph. 

ascendens, Placodium (fiavescens) sympageum, PL pyraceum, PL citrinum, 

Candelariella vitellinum, Rinodina exigua, Lecanora campestris, L. umbrina, 

L. galactina, Lecania erysibe, Bacidia inundata. Xanthoria parietina is one 

of the commonest wandering species; it was found by Richard 1 on an old 

cannon lying near water, that was exfoliated by rust. 

On tar Lecanora nmbrina. 

On charcoal Rinodina exigua, Lecanora umbrina. 

On bones Xanthoria parietina, Physcia ascendens, Ph. tenella, Placodium 

citrinum, PL lacteum, Rinodina exigua, Lecanora galactina, L. dispersa, L. 

nmbrina, Lecania erysibe, L. cyrtella, Acarospora pruinosa, A. Heppii, Bacidia 

inundata, B. muscorum, Verrucaria anceps, V. papillosa. 

In Arctic regions in Ellesmere Land and King Oscar Land, Darbishire 2 

found on bones : Lecanora varia, L. Hageni, Rinodina turfacca and Buellia 

parasema (disciformis). He could not trace any effect of the lichens on the 

substratum. 

On charcoal Rinodina exigua, Lecanora umbrina. 

On dross or clinkers Parmelia dubia, Physcia obscura, Ph. ascendens 

f. tenella, Ph. pulverulenta, Xanthoria parietina, Placodium pyraceum, PL 

citrinum, Rinodina exigua, Lecanora dispersa, L. umbrina, Lecania erysibe. 

On glass 3 

Physcia ascendens f. tenella, Buellia canescens. Richard has 

recorded the same lichens on the broken glass of walls and in addition : 

Xantlioria parietina, Lecanora crenulata, L. dispersa, Lecania erysibe, Rinodina 

exigua, and Buellia canescens. 

On earthenware, china, etc. Physcia ascendens f. tenella, Lecanora 

umbrina, L. dispersa, Lecania (? Biatorind) cyrtella, Verrucaria papillosa, 


On leather Nearly fifty species or varieties were found by Lesdain on 

old leather on the dunes. Cladonias, Parmelias and Physcias were well represented 

with one Evernia and a large series of crustaceous forms. He 

adds a note that leather is an excellent substratum 

: lichens covered most 

of the pieces astray on the dunes. Similar records have been made in 

Epping Forest by Paulson and Thompson 4 who found Cladonia fi mbriata 

var. tubaeformis and Lecidea granulosa growing on an old boot. These 

authors connect the sodden condition of the leather with its attraction for 

lichens. 

On pasteboard Even on such a transient substance as this Lesdain 

found a number of forms, most of them, however, but poorly developed : 

Cladonia furcata (thallus), Parmelia subaurifera (beginning), Xanthoria 

parietina (beginning), Physcia obscura, Placodium citrinum (thallus), PL 

1 Richard 1877. 


3 Cf. p. 234. 

4 Paulson and Thompson 1913.

378 

ECOLOGY 

pyraceum, Lecanora umbrina, Bacidia inundata and Polyblastia Vouauxi var. 

charticola. 

On linoleum Xanthoria parietina, Physcia ascendens f. tenella, Rinodina 

exigua, Lecanora umbrina. 

On indiarubber Physcia ascendens f. tenella. 

On tarred cloth Xanthoriaparietina, Placodium citrinum, PI. pyraceum, 

Rinodina exigua, Lecanora umbrina, Lecania erysibe, Bacidia inundata. 

On felt Bacidia inundata, B. muscorum. 

On cloth (cotton, etc.) Bacidia inundata. 

On silk Physcia ascendens, Ph. obscura, Placodium citrinum (thallus), 

Lecanora umbrina, Bacidia inundata. 

On cord Physcia ascendens f. tenella, Placodium citrinum (thallus). 

On excreta One would scarcely expect to find lichens on animal 

droppings, but as some of these harden and lie exposed for a considerable 

time, some quick-growing species attain to more or less development on 

what is, in any case, an extremely favourable habitat for fungi and for many 

minute organisms. Paulson and Thompson found tiny fruiting individuals 

of Cladonia macilenta and Cl. fimbriata var. tubaeformis growing on the dry 

dung of rabbits in Epping Forest. On the same type of pellets Lesdain records 

Physcia ascendens f. leptalea, Cladonia pyxidata, Bacidia inundata and 

B. muscorum ; and on sheep pellets : Physcia ascendens f. leptalea and Placodium 

citrinum; while on droppings of musk-ox in Ellesmere Land Darbishire 

found Biatorina globulosa, Placodium pyraceum, Gyalolechia subsimilis, Leca- 

nora epibryon, L. verrucosa, Rinodina turfacea and even, firmly attached, 

TJiamnolia vermicularis. 

It would be difficult to estimate the age of these lichens, but it seems 

evident that the " wanderers " are all more or less quick growers, and the 

lists also prove conclusively their complete indifference to the substratum, 

as the same species occur again and again on the very varied substances. 

5. 

LOCALIZED COMMUNITIES 

Lichens may be grouped ecologically under other conditions than those 

of substratum. They respond very readily to special environments, and 

associations arise either of species also met with elsewhere, or of species 

restricted to one type of surroundings. Such associations or communities 

might be multiplied indefinitely, but only a few of the outstanding ones 

will be touched on. 

a. MARITIME LICHENS. This community is the most specialized of any, 

many of the lichens having become exclusively adapted to salt-water sur- 

roundings. They are mainly saxicolous, but the presence of sea-water is the 

factor of greatest influence on their growth and distribution, and they occur

indifferently on any 


kind of shore rock either siliceous or calcareous. 

Wheldon and Wilson 1 noted this indifference to substratum on the Arran 

shores, where a few calcicolous species such as Verrucaria nigrescens, V. 

macultfornris, Placodium tegularis and PL lobu/atuin, grow by the sea on 

siliceous rocks. They suggest that the spray-washed habitat affords the 

conditions, which, in other places, are furnished by limestone. 

The greater or less proximity of the salt water induces in lichens, as in 

other maritime plants, a distribution into belts or zones which recede 

gradually or abruptly according to the slope of the shore and the reach of 

the tide. Weddell 2 on the Isle d'Yeu delimited three such zones : ( i ) marine, 

those nearest the sea and immersed for a longer or shorter period at each 

tide; (2) semi-marine, not immersed but subject to the direct action of the 

waves, and (3) maritime or littoral, the area beyond the reach of the waves 

but within the influence of sea-spray. In the course of his work he indicates 

the lichens of each zone. 

Fie. 122. Ramalina siliqtiosa A. L. Sm. Upper zone of barren plants (after M. C. Knowles, 

R. Welch, Photo.}. 

In Ireland, a thorough examination has been made of a rocky coast at 

recognizes five distinct belts 

Howth near Dublin by M. C. Knowles 3 . She 


' Weddell 1875. 

Knowles 1913.

380 

ECOLOGY 

beginning with those furthest from the shore though within the influence of 

the salt water: 

1. The Ramalina belt. 4. Verrucaria maura belt. 

2. The Orange belt. 5. The belt of Marine Verrucarias. 

3. 

Lichina Vegetation. 

(i) The Ramalina belt. In this belt there are two zones of lichen vegetation: 

those in the upper zone consist mainly of barren plants of Ramalina 

siliguosa 1 

rather dark or , glaucous in colour with much branched fronds 

which are incurved at the tips (Fig. 122). They are beyond the direct action 

of the waves. The lower zone consists also mainly of the same Ramalina, 

the plants bearing straight, stiff, simple, or slightly branched fertile fronds 

of a pale-green or straw colour (Fig. 123). The pale colour may be partly 

due to frequent splashings by sea-spray. 

Ramalina siliquosum in both zones takes several distinct forms, according 

to exposure to light, wind or spray, the effects of which are most marked in 

the upper zone. The plants growing above the ordinary spray zone generally 

form sward-like growths (Fig. 124); at the higher levels the sward growth 

is replaced by isolated tufts with a smaller more amorphous thallus which 

passes into a very small stunted condition. The latter form alone has 

gained and retained a footing on the steep faces of the hard and close- 

grained quartzite rocks. "On the western faces, indeed, it is the only visible 

vegetation." The dwarfed tufts with lacerated fronds measuring from 

\ to \ an inch in height are dotted all over the quartzites. On the sea faces 

the plants are larger, but everywhere they are closely appressed to the rock 

surface. At lower levels the fronds lengthen to more normal dimensions. 

"On these steep rock-faces there is a complete absence of any of the 

crustaceous species. The problem, therefore, as to how the Ramalina has 

obtained a foothold on these very hard precipitous rocks, which are too 

inhospitable even for crustaceous species is an interesting and puzzling one." 

In the Ramalina zone along with the dominant species there occur 

occasional tufts ofR. Cnrnowii and R. subfarinacea, the latter more especially 

in shady and rather moist situations. There are also numerous foliaceous 

and crustaceous lichens mingling with the Ramalina vegetation (Fig. 125), 

several Parmelias, Physcia aquila, Xanthoria parietina, Buellia canescens, 

B, ryssolea, Lecanora atra, L. sordida, Rhizocarpon geographicum and others. 

In the main these are arranged in the following order descending towards 

the sea : 

1. Parmeliae. 3. Xanthoria parietina, 

2. Physcia aquila. 4. Crustaceous species. 

1 The two morphologically similar plants Ramalina cuspidata and R. scopulorum are here 

united under the older name R. siliquosa. The distinction between the two is based on reaction 

tests with potash, which give very uncertain results.

LICHEN COMMUNITIES 

123. Ramalina siliqitosa A. L. Sm. Lower zone of fertile plants (after M. C. Knowles, 

R. Welcli, Photo.}. 

Fig. 1 24. Sward of young Ramalinae (after M. C. Knowles, R. Welch, Ph*

382 

ECOLOGY 

Parmelia prolixa is the most abundant of the Parmelias : it covers large 

spaces of the rocks and frequently competes for room with the Ramalinas, 

or in other areas with PJiyscia aquila and Lecanora parella. 

A number of crustaceous species which form the sub-vegetation of the 

Ramalina belt, and also on the same level, clothe the steeper rock faces 

where shelter and moisture are insufficient to support the foliose forms. 

"In general the sub-vegetation of the eastern and northern coasts is largely 

composed of species that are common in Alpine and upland regions. This 

Fig. 125. Crustaceous communities in the Ramalina belt. Lecanora atra Ach. (grey patches) and 

Buellia ryssolea A. L. Sm. (dark patches). (After M. C. Knowles, R. Welch, Photo.) 

is due to the steepness of the rocks and also to the colder and drier conditions 

prevailing on these coasts." An association of Rhizocarpon geographicum, 

Lecanora (sordida) glaucoma and Pertusaria concreta f. Westringii forms an 

almost continuous covering in some places, descending nearly to sea-level. 

On sunnier and moister rocks with a south and south-west aspect the 

association is of more lowland forms such as Buellia colludens, B. stelhdata 

Lecanora smaragdula and L. simplex f. strepsodina. 

(2) The Orange belt. "Below the Ramalinas, and between them and 

the sea, several deep yellow or orange-coloured lichens form a belt of varying


width all round the coast. In summer, the colour of these lichens is so 

brilliant that the belt is easily recognized from a considerable distance." The 

most abundant species occur mainly in the following order descending 

towards the sea : 

1 . Xanthoria parietina. 4. Placodium deripiens. 

2. Placodium murorum. 5. Placodium lobulatum. 

3. Placodium tegular is. 

"On the stones and low shore rocks that lie just above the ordinary hightide 

level Placodium lobulatum grows abundantly, covering the rocks with 

a continuous sheet of brilliant colour." With these brightly coloured lichens 

are associated several with greyish thalli such as : 

Lecanora prosechoides. Biatorina lenticularis, 

Lecanora uinbrina. Rinodina exigua var. demissa. 

Lecanora Hageni. 

Rhizocarpon 

Opegrapha calcarea f. hctcromorpha. 

alboatrum. 

(3) The Lichina vegetation, and (4) The Verrucaria maura belt. 

These two communities are intermingled, and it will therefore be better to 

consider them together. There are only two species of Lichina on this or any 

other shore, L. pygniaea and L. confiuis; the latter grows above the tide-level, 

and sometimes high up on the cliffs, where it is subject to only occasional 

showers of spray: it forms on the Howth coast a band of vegetation four 

to five inches wide above the Verrucaria belt. Lichina pygniaea occurs 

nearer the water, and therefore mixed with and below Verrucaria maura. 

Those three zones were first pointed out by Xylander 1 

at Pornic, where 

however they were all submerged at high tide. 

Verrucaria maura is one of the most abundant lichens of our rocky 

coasts, and is reported from Spitzbergen in the North to Graham Land in 

the Antarctic. It grows well within the range of sea-spray, covering great 

stretches of boulders and rocks with its dull-black crustaceous thallus. At 

Howth it is submerged only by the highest spring tides. it is Though the 

dominant lichen on that beach, other species such as V. memnonia, V. promi- 

nula, and V. aquatilis form part of the association, and more rarely V. scotitia 

along with Arthopyrenia halodytes, A. leptotera and A. Iializoa. 

(5) The belt of marine Verrucarias. This association includes the 

species that are submerged by the tide for a longer or shorter period each 

day. The dominant species are Verrucaria microspora, V. striatnla and 

V. uiucosa. Arthopyrenia halodytes is also abundant; A. halizoa and A. 

marina are more rarely represented. Among the plants of Fucus spiralis, 

Verrucaria mucosa, the most wide-spreading of these marine forms, is "very 

conspicuous as a dark-green, almost black, band of greasy appearance 

stretching along the shore." When growing in the shade, the thallus is of 

a brighter green colour. 

1 

Nylander 1861.

384 

ECOLOGY 

An examination 1 of the west coast of Ireland yielded much the same 

results, but with a still higher " white belt " formed mainly of Lecanora 

parella and L. atra which covered the rocks lying above high-water mark, 

"giving them the appearance of having been whitewashed." A more 

general association for the same position as regards the tide is given by 

Wheldon and Wilson 2 on the coasts of Arran as : 

Physcia aquila. 

Placodium tegularis. 

Xanthoria parietina. 

Ramalina cuspidata. 

Lecanora parella. Physcia stellaris. 

Lecanora atra. Physcia tenella. 

Lecanora campestris. 

Verrucaria maura. 

Placodium ferrugineum vzx.festivum. 

A somewhat similar series of "formations" was determined by Sandstede 3 

on the coast of Riigen. On erratic granite boulders washed by the tide he 

found : 

Verrucaria maura. Lecanora prosechoides. 

Lichina confinis. 

Placodium lobulatum. 

While in a higher position on similar boulders : 

Lecanora exigua. 

Lecanora dispersa. 

Lecanora galactina. 

Lecanora parella. 

Lecidea colludens. 

Lecidea lavata. 

Lecanora sulphurea. Lecidea nigroclavata f. lenticularis. 

Lecanora saxicola. Xanthoria parietina and f. aureola. 

Lecanora caesiocinerea. Physcia subobscura. 

Lecanora gibbosa. Physcia caesia. 

Lecanora atra. 

And more rarely a few species of Lecidea. 

b. LICHENS OF SAND-DUNES. These lichens might be included with those 

of the terricolous communities, but they really represent a maritime com- 

munity of xerophytic type, subject to the influence of salt spray but not 

within reach of the tide. They are sun-lichens and react to the strong light 

in the deeper colour of the thallus. In such a sun-baked area at Findhorn 

a luxuriant association of lichens was observed growing among short grass 

and plant debris. It consisted chiefly of: 

Parmelia physodes. 

Cladonia ceriricornis. 

Evernia prunastri. . Cladonia endiinaefolia. 

Cetraria aculeata. Peltigera spp. 

On very arid situations the species of Cladonia are those that have a well- 

because such a thallus is 

developed rather thick primary thallus, probably 

able 4 to retain moisture for a . prolonged period On shifting sand, as in the 

desert, there are no lichens; it is only on surfaces more or less fixed by marram 

1 Knowles 1915. 


3 Sandstede 1904. 

4 Aigret 1901.

LICHEN COMMUNITIES: 385 

grass that lichens begin to develop, though in the cool damp weather of 

autumn and winter, as observed by Wheldon and Wilson 1 

certain , 

species 

associated with Myxophyceae, such as Collemaceae, may make their appearance, 

among others Leptogium scotinum, Collemodium turgidum and Collcma 

ceranoides. Watson 2 makes the same observation in his study of sand-dunes. 

When the loose sand on the dunes of South Lancashire becomes cemented 

by algae and mosses several rare Lecideae are to be found on the decaying 

vegetation, and with further accumulation of humus Cladoniae appear and 

spread rapidly along with several species of Peltigera and the ubiquitous Parmelia 

physodes. The latter starts on dead twigs of Salix repens and spreads 

on to the surrounding soil where it forms patches some inches in diameter. 

The association also includes Lecidea uliginosa and Bilimbia sphacroides. 

On the more inland portions of the dunes numerous rather poorly de- 

veloped Cladoniae and Cetraria aculeata were associated, while on the sides 

of "slacks" or "dune-pans" Colleina pulposum, Cladonia sylvatica and several 

crustaceous lichens covered the soil. The wetter parts of the dunes were 

not found to be favourable to lichen growth. 

Sandstede 3 found on the sandy shores of Riigen, from the shore upwards: 

first a stretch of bare sand, then a few dune grasses with scattered scraps 

of Cladoniae, Peltigerae and Cetraria aculeata. Next in order sandbanks 

with Parmelia physodes, Cladonia sylvatica, Cl. alcicornis and Stereocanlon 

pascliale. All these are species that occur on similar shores in the British 

Islands. Sandstede adds an extensive list of maritime species observed by 

him in Riigen. 

A very careful tabulation of lichens at Blakeney Point in Norfolk was 

made 'by McLean 4 and the table on p. 386 is reproduced from his paper. 

Sand, he writes, is present in all the associations and the presence or 

absence of stones marks the great difference between the two formations 

determined by dune and shingle. 

(1) Bare sand, which is the first association listed, is an area practically 

the few lichen plants, Cladonia furcata and Cetraria 

without phanerogams ; 

aculeata f. acanthella, are attached by slight embedding 

in the soil. 

(2) Grey dune. The sand-loving lichens of the associatipn grow in 

company with Hypnnm cupressiforme and attain their greatest development. 

Other species which also occur there are Parmelia physodes and Evertiia 

prunastri var. stictocera. 

(3) Derelict dune. This part of the dune formation occurs here and 

there on the seaward margin where the grey dune has been worn down by 

the wind. It is more shingly, hence the presence of stone lichens; dune 

phanerogams are interspersed and with them a few fruticose lichens, such as 

Cladonia furcata. 


S. L. 

- Watson 1918'. 

3 Sandstede 1904. 

* McLean 1915. 

2 5

386 

ECOLOGY 

(4) High shingle. The term indicates shingle aggregated into banks 

lying well above all except the highest tides. A large percentage of sand 

may be mixed with the stones and if no humus is present and the stones of 

small size, lichens may be absent altogether. Those occurring in the "loose 

shingle" are saxicolous. In the "bound shingle" where there is no grass 

the stones, fixed in a mixture of sand and humus, are well covered with 

lichens. With the presence of grass, a thin layer of humus covers the stones 

and a dense lichen vegetation is developed both of shingle and of dune 

species. 

(5) Low shingle. This last association lies in the hollows among plants 

of Suaeda fruticosa. Stability is high and tidal immersions regular and 

frequent. The dominant factor of the association is the quantity of humus 

and mud deposited around and over the stones. The lichens cover almost 

every available spot on the firmly embedded pebbles. The characteristic 

species of such areas are Lecanora badia and L. (Placodinm) citrina which 

effect the primary colonization. To these succeed Lecanora atra and Xan- 

thoria parietina. In time the mud overwhelms and partly destroys the 

lichens, so that the phase of luxuriant growth is only temporary. 

Lecanora badia is conspicuously abundant at the sand end of this forma- 

tion. Lecanora (Placodium} citrina disappears as the mud is left behind. 

Collema spp. also occur frequently on the mixture of mud and sand round 

the stones. Trie species on " low shingle " are those most tolerant of sub- 

mersion : Verrucaria maura is confined to this area, where it is covered by 

the tide several hours each day. 

FORMATION 

Dune 

Shingle 

i. Bare Sand 

2. Grey Dune 

ASSOCIATION 

Derelict Dune 

4. High Shingle I 

Loose j 

(Without sand 

Bound 

PRINCIPAL SPECIES 

Cetraria aculeata f. acanthella 

Cladonia furcala 

Cladonia rangiferina, Peltigera rufescens 

Cladonia furcata, Cl. alcicomis 

Cladonia furcata, Parmeliafuliginosa 

Rhizocarpon confervoides 

(Lecanora atra, L. galactina 

With sand -I Rhizocarpon confervoides 

{Lecanora citrina 

With grasses 

(Physcia tenella, Lecanora citrina, Xanthoria parietina 

\ Squamaria saxicola 

I Parnielia saxatilis, P. fuliginosa 

\ Cladonia rangiferina, Cl. furcata, Cl. pungens 

\ Cetraria aculeata 

Xanthoria parietina, Biatorina chalybeia, Lecanora atn 

Aspiciliagibbosa, 

5. Low Shingle 

Buellia colludens, J'errncaria (Without grasses 

microspon 

Physcia tenella, Lecanora atroflava 

Rhizocarpon confervoides, Lecanora citrina var. incrustan. 

L. badia, L. atra, Xanthoria parietina 

Verrucaria maura 

McLean adds that Xanthoria parietina in its virescent form on Suaeda 

fiuticosa also endures constant immersion ; Lecanora badia does not occur


above the tidal line and Lecanora galactina does not descend below tidal 

limits ; the latter is an arenicolous species and colonizes some of the loosest 

and sandiest areas of shingle. Rhizocarpon confewoides is ubiquitous. 

c. MOUNTAIN LICHENS. On the mountain summits of our own and 

other lands are to be found lichens very similar to those of the far North 

the climatic conditions being the chief factors of importance in determining 

the formations. These regions are occupied by what Wheldon and Wilson 1 

describe as " a zone of Arctic-Alpine vegetation," and they have recorded 

a series of lichen associations belonging to that zone on the schistose 

summits of the Perthshire mountains. The following is one of the most 

typical : 

Euopsis granatina. 

Sphaerophorus coralloides. 

Spliaerophorus fragilis. 

Gyrophora polyphylla. 

Cetraria tristis. 

Cetraria nii/alis. 

Lecanora tartarea vvx.frigida. 

Lecanora upsaliensis. 

Aspicilia ocitlata. 

Pertusaria dactylina. 

Pertusaria glomerata. 

Stereocaulon denudatum. 

Parmelia saxatilis. Parmelia alpicola. 

Parinelia omphalodes. Cetraria aculeata. 

Parmelia lanata. 

Cetraria crispa. 

Parmelia stygia. 

Cetraria islandica. 

Stereocaulon tomentosum. Lecidea limosa. 

Stereocaulon alpinum. 

Cladonia coccinea. 

Cladonia gracilis. 

Cladonia uncialis. 

Cladonia destricta. 

Cladonia racemosa. 

Lecidea arctica. 

Lecidea alpestris. 

Lecidea demissa. 

Lecidea tiliginosa. 

Lecidea citprea. 

Lecidea Berengeriana. 

Lecidea cupreiformis. 

Lecidea atrofusca. 

Again on the summit of Ben-y-Gloe the same authors 2 have recorded 

" 

Gyrophora erosa, G. torrefacta and G. cylindrica, Pannelid alpicola, Lecanora 

tartarea var. frigida, Lecidea limosa and L. arctica, the last two lichens 

thriving in the most bleak and exposed 

situations. Cladonia cen>icornis 

grew in reduced squamulose cushions ; Stereocaulon and SpJiacrophorus in 

very compact forms, the outer stalks prostrate, the next inclined, the central 

ones erect so that points only are exposed and no lateral stress is caused by 

wind storms. Erect fruticose lichens are absent in this region, being represented 

only by Parmelia lanata, a semi-decumbent plant, and by Tliainnolia 

rcnnicularis which is prostrate on the ground except where the points of 

the stalks turn up to catch the dew. Many of the Lecideae were observed to 

have large fruits and very little thallus : 

" 

the hyphae ramify in the minute 

interstices of the stone and the gonidia cluster under the lea of the apothecia; 

this is especially the case on loose stones where conditions are extremely 

dry." 

On the Continent an interesting study of the lichens of high altitudes 

was made by Maheu 3 in the Savoyard Oberland. On the Great Casse at 



1 Maheu 1887. 

25 

:

3 88 ECOLOGY 

a height of 3861 m. he collected four mosses and sixteen lichens. These 

were : 

Stereocaulon condensation, Candelaria concolor. Buellia discolor. 

Gyrophora cylindrica 

Gyrophora spodochroa. 

Caloplacapyracea var . nivalis. 

Haematomma ventosum. 

Buellia stellulata. 

Lecidea contigua var. steriza 

Solorina crocea. Acarospora smaragdula. Lecidea confluens. 

Solorina saccata. Psora decipiens. Dermatocarpon hepaticum. 

Parmelia encausta. 

He found that as he climbed higher and higher foliaceous species became 

rarer and crustaceous more abundant. The colour of the lichens on the high 

summits was slightly weakened and the thallus often reduced, but all were 

fertile and the apothecia normal and sporiferous. Lichens at less high 

altitudes where they emerge from the snow covering for longer periods and 

enjoy light and sunshine are, as already observed, often very brightly 

coloured and of luxuriant growth. 

d. TUNDRA LICHENS. In phyto-geography the term "tundra" is given 

to great stretches of country practically treeless and unsheltered within the 

Polar climate; the tundra extends from the zone of dwarfed trees on to the 

permanent ice or snow fields. The vegetation includes a few dwarfed trees, 

shrubs, etc., but is mainly composed of mosses and lichens ; the latter being 

the most abundant. These are true climatic lichen formations. 

Leighton 1 

in , describing lichens from Arctic America brought home by 

" 

the traveller, Sir John Richardson, quotes from the latter that : the terrestrial 

lichens were gathered on Great Bear, and Great Slave Lakes before 

starting on our summer voyages after the snow had melted.... The barren 

grounds are densely covered for many hundreds of miles with Corniculariae 

and Cetrariae, and where the is ground moist with Cladoniae, while the 

boulders thickly scattered over the surface are clothed with Gyrophorae.... 

The smaller stones on the gravelly ridges of the Barren Grounds are 

covered with lichens." 

The accounts of tundra lichens that have been given by various travellers 

deal chiefly with the more prominent terricolous forms. They 

have been 

classified as "Cladina tundra," including Cladonia rangiferina and Sphaerophorus 

coralloides, " Cetraria tundra," and " Alectoria heath," the latter the 

hardiest of all. Great swards of these lichens often alternate with naked 

stony soil. 

Kihlman 2 has noted, as characteristic of tundra formations, the compact 

cushion-like growth of the mosses which are thus enabled to store up water 

and to conduct it by capillarity throughout the mass to the highest stalks. 

Certain tundra lichens take on the same growth character as adaptations to 

the strenuous life conditions. Cetraria glauca f. spadicea with f. congesta and 

1 


2 Kihlman 1890. .

LICHEN COMMUNITIES - 

C. crispa are examples of this : compact growth they form a soft thick carpet 

of a yellowish-grey colour. Cladoniae also grow in crowded tufts, but are 

generally to be found in the more sheltered positions, in valleys between 

the tundra hills and in the clefts of the rocks, or between great boulders and 

stones where there is also more moisture. 

The same kinds of lichens occur all over these northern regions. Birger 

Nilson 1 

gives as the principal earth-lichens in Swedish Lappland, Alectoria 

ochroleuca, A. nigricans, Cetraria nivalis, C. cucullata, Cladonia uncialis, 

Tkamnolia (Cerania) vermicularis and Sphaerophorus coralloides. 

Darbishire 2 

389 

speaks of the extensive beds of various species of Cetraria 

in Ellesmere Land and King Oscar Land. Alectoria nigricans and A.oc/iro- 

lenca were often found in pure communities, but even more frequently in close 

company with mosses. Though these fruticose lichens are not represented 

by many species in Arctic regions, they cover a very extensive area and 

form a very important feature in the vegetation. 

Crustaceous lichens are not wanting : Lecanom 

tartarea f. frigida, L. 

epibryon and others are to be found in great sheets covering the mosses or 

the soil, or spreading over the stones and boulders. Cold has no deterrent 

effect, and their advance is only checked by the presence of perpetual snow. 

e. DESERT LICHENS. The reduced rainfall of desert countries is un- 

favourable to general lichen growth and only the more xerophytic species 

those with a stout cortex can flourish in the adverse conditions of excessive 

light and dryness. Lichens, however, there are, in great numbers as far as 

individuals are concerned, though the variety is not great. The abundance 

of the crustaceous Lecanora esculenta in the deserts of Asia has already been 

noted. Flagey 3 found it one of the dominant species at Biskra in the Sahara 

1 where it grows on the rocks. Patouillard 4 in describing the flora of Tunis 

of Lecanora crassa f. deserti which at 

speaks of the great patches (societies) 

a distance look like milk spilled on the ground, or if growing on unequal 

surfaces take the aspect of plaster that has been passed over by some 

wheeled vehicle. At Biskra species of Heppia grow on the sand. Steiner 5 

also records the frequency of Heppia and of Endocarpon in the Sahara as well 

as of Gloeolichens which, as they are associated with gelatinous blue-green 

algae, can endure extreme and long-continued desiccation. These lichens, 

however, only form communities in clefts among the rocks where these abut 

on the desert. In the great plains the sand is too mobile and too often 

shifted by the sirocco to enable them to settle. 

Bruce Fink 6 discusses desert lichens and their adaptive characters : 

crustaceous species with a stout cortex are best able to withstand the long 

dry periods; conspicuously lobed thalli are lacking, as are lichens with 

1 2 Nilson 1907. 


5 

Steiner 1895. 

3 

4 

Flagey 

Patouillard 

1901. 

1897. 

6 Bruce Fink 1909.

390 

ECOLOGY 

fruticose structure though he thinks the latter are prevented from developing 

by the exposure to high winds and driving sand storms. 

1 

Herre's study of 

the desert lichen flora at Reno, Nevada, is full of interest. The district is 

situated at an altitude of 4500 feet east of the Sierra Nevada Mountains. 

The annual rainfall averages 8'2i inches, and a large part falls as snow during 

the winter months or as early spring rain. The summer is hot and dry and 

the diurnal changes of temperature are very great. Strong drying winds 

from the west or north are frequent. 

At 5000 feet and upwards lichens are, in general, exceedingly abundant 

on all rock substrata and represent 57 species or subspecies, only three of 

these being arboreal: Buellia triphragmia occurs rarely, Xanthoria polycarpa 

is frequent on sage brush, while Candelariella cerinella though a rocklichen 

grows occasionally on the same substratum. Caloplaca (Placodiuni) 

elegans is one of the most successful and abundant species and along with 

Lecanora (nine forms), Acarospora (seven forms) and Lecidia (five forms) com- 

prises three-fourths of the rock surface occupied by lichens. The addition 

of Rinodina with two species and Gyrophora with four brings the computation 

of individuals in these desert rock formations up to nine-tenths of the whole. 

As the desert rocks pass to the Alpine, Gyrophora becomes easily the domi- 

nant genus followed by Acarospora, Caloplaca and Lecidea, 

"The colouring characteristic of the rock ledges of the desert and canon 

walls is often entirely due to lichens, and in a general way they form the 

only brilliant plant formations in a landscape notable for its subdued pale 

monotonous tones. Most conspicuous are Acarospora chlorophana and 

Caloplaca elegans, which form striking landmarks when covering great crags 

and rock walls. The next most conspicuous lichens are Rinodina oreina and 

Lecanora rubina and its allies, which often entirely cover immense boulders 

and northerly sloping rock walls." Herre concludes that though desert con- 

ditions are unfavourable to most species of lichens, yet some are perfectly 

at home there and the rocks are just as thickly covered as in regions of 

greater humidity and less sunshine. 

f. AQUATIC LICHENS. There is only one of the larger lichens that has 

acquired a purely aquatic habit, Hydrothyria venosa, a North American 

them often with 

plant. It grows on rocks 2 in the beds of streams, covering 

a thick felt ; it is attached at the base and the rather narrow fronds float 

freely in the current. The gonidium is Nostoc sp., and the thallus is of a 

bluish-grey colour ; the fruits are small discoid reddish apothecia with an 

evanescent margin. It is closely allied to Peltigerae, some of which are 

moisture-loving though not truly aquatic. 

The nearest approach to aquatic habit among the foliose forms in our 

1 Herre 191 1 2 . 2 See p. 97.


country is Dennatocarpon aquaticum, with thick coriaceous rather contorted 

lobes; it inhabits rocks and stones in streams and lakes. Somewhat less con- 

tinuously aquatic is D. ininiatum var. complicatum which grows on damp rocks 

exposed to spray or occasionally to inundation. Lindsay 1 has described it 

" 

on boulders by the side of the Tay, frequently covered by the river when 

flooded, and of a deep olive colour when under water": both these lichens 

have a wide distribution in Europe, Africa, America and New Zealand. 

In a discussion of lake shore plants Conway Macmillan 2 describes on 

the flat shores a Dennatocarpon zone on the wet area nearest the lake, behind 

that a Biatora zone and further landward a Cladonia zone. On rounded 

rocky shores the same zones followed each other but were less broad : they 

were so close together that the Cladoniae, which with Stereocaulon paschale 

grow in profusion on all such shores, occurred within a couple of feet of the 

high-water mark. 

M. C. Knowles 3 

the lichen flora of some mountain 

reports concerning 

lakes in Waterford, that a band of Dennatocarpon miniatuin var. complicatum 

six feet wide grew all the way round the lakes between the winter and 

summer level of the water. Below that zone D, aquaticum formed another 

belt mingled with the moss Fontinalis and several species of crustaceous 

lichens Staurotheleae^ Polyblastiae, etc. 

Bruce Fink 4 

gives as a typical "amphibious angiocarpous lichen formation" 

of wet rocks in Minnesota: Dennatocarpon aquaticum, D. miniatuin var. 

complicatum, Staurotliele clopima and Verrucaria viridula. These " forma- 

" 

tions," he says, may be seen complete in places along the shores of Vermillion 

Lake and less well represented at other portions of the lake shore." 

Macmillan found that on the rocky shores of Lake Superior the Dermato- 

carpon zone also occurred nearest the water. 

Species with closed fruits such as Pyrenolichens, or with apothecia 

deeply sunk in the thallus and thus also well protected, seem to be best 

adapted to the aquatic life. Such in our own country are Lecanora lacustris, 

Bacidia inutidata and others, with a number of Verrncariae : V. aethiobola, 

V. hydrela, V. margacea, etc. 

Lettau 5 

in Thuringia : 

gives as "formations" on rocks or boulders in the beds of streams 

Verrucaria aethiobola. 

Verrucaria hydrela. 

Dermalocarpon aquaticum. 


Lecanora aquatica. 

In their ecological study of Perthshire lichens Wheldon and Wilson 6 

give two " formations." The first is on rocks submerged for long periods, 

1 

2 4 

Lindsay 1856. 

Macmillan 1894. Knowles in lift. 

Bruce Fink 1903. 

5 * 

Lettau 1. 

Wheldon and Wilson 

191 1915.

39 2 

ECOLOGY 

though in dry weather the lichens may be exposed, and can withstand 

desiccation for a considerable time : 

Pterygium Kenmorensis. Lecidea contigua. 

Collema fluviatile. 

Lecidea albocoerulescens. 

Lecanora lacustris. Dermatocarpon miniatum var. complicaium. 

Lecanora epulotica. Dermatocarpon aquaticutil. 

Bacidia inundata. Verrncaria laevata. 

Rhizocarpum obscuratum. Verrucaria aethiobola. 

Rhizocarpum petraeum. 

Verrucaria margacea. 

The second group of species usually inhabits damp, shaded rocks of 

ravines or large boulders by streams or near waterfalls. It includes species 

of Collema, Sticta, Peltigera, Solorina, Pannaria, etc., with Opegrapha zonata, 

Porina lectissima and Verrucaria nigrescens. 

The last-mentioned lichen grows by preference on limestone, but in 

excessive moisture 1 

importance. 

, 

as by the sea-side, the substratum seems to be of minor 

D. LICHENS AS PIONEERS 

a. SOIL-FORMERS. The part played by lichens in the "Economy of 

Nature" is of very real importance: to them is allotted the pioneer work 

of breaking down the hard rock surfaces and preparing a soil on which 

more highly developed plants can grow. This was pointed out by Linnaeus 2 

who thus describes the succession of : plants "Crustaceous lichens," he 

writes, "are the first foundation of vegetation. Though hitherto we have 

considered theirs a trifling place among plants, nevertheless they are of 

great importance at that first stage in the economy of nature. When the 

rocks emerge from the seas, they are so polished by the force of the waves, 

that scarcely any kind of plant could settle on them, seen more especially 

near the sea. But very soon, in truth, the smallest crustaceous lichens begin 

to cover those arid rocks, and are sustained by minute quantities of soil and 

by imperceptible particles brought to them by rain and by the atmosphere. 

These lichens in time become converted by decay into a. thin layer of 

humus, so that at length imbricate lichens are able to thrust their rhizoids 

into it. As these in turn change to humus by natural decay, various mosses 

such as Hypnum, BryuDi and Polytrichum follow, and find suitable place 

and nourishment. In time there is produced by the dying down of the 

mosses such a quantity of soil that herbs and shrubs are able to establish 

themselves and maintain their existence." 

Similar observations have been made since Linnaeus's day, among others 

by Guembel 3 in his account of Lecanora ventosa. Either by the excretion of 

carbon dioxide which acidifies the surrounding moisture, or by the mechanical 



3 Guembel 1856.

LICHENS AS PIONEERS 393 

action of hyphae and rhizinae, the component particles of rocks such as 

granite are gradually dissolved and broken up. Rocks exposed to weather 

alone are unchanged, while those covered with lichens have their surface 

disintegrated and destroyed. 

The decaying parts of the lichen thallus add to the soil material as 

observed by Linnaeus, and in time mosses follow, and, later, phanerogams. 

Goeppert 1 has pointed out the succession observed on roofs of houses as: 

"first some lichen such &s' Lecanora saxicola, then the moss Griuitnia pitlvi- 

iiata, which forms compact cushions on which later grow Poa compressa, 

small crucifers, etc." 

Goeppert 1 has noted as special rock-destroyers some foliaceous species, 

Parmelia saxatilis, P. stygia and P. encausta, the underlying rock being 

roughened and broken up by their rhizoids. Species of Gyroplwra and 

Sphaerophorus have the same disintegrating effect, so that the surface of the 

rock may in time lose its coherence to a depth of 2 to 4 inches. Crustaceous 

species such as Lecanora polytropa, Candelariella vitellina, etc., exercise an 

equally powerful solvent action, while underneath closely appressed growers 

like Lecanora atra and Acarospora smaragdula the stone is converted to 

a friable substance that can be sliced away with a knife. 

Salter- concluded that oxalic acid was the principal agent in disintegration. 

He found that it acted more or less rapidly on minerals and almost 

any class of saline compounds; it even attacked glass finely powdered, 

though silica remained unchanged. 

Bachmann 3 found that granite was reduced by lichens to a clay-like 

granular yellow mass in a comparatively short time, the lichen seizing on 

the particles of mica first; but the spread of the lichen over the rock, he 

observes, is largely directed by the amount of humidity and by the chance 

of gaining a foothold. In the case of calcareous rocks he 4 tested the relative 

dampness of those containing lichens and those that were lichen-free. In 

the former case water was absorbed more freely and retained much longer 

than in the barren rock, thus encouraging further vegetation. 

Lucy E. Braun 5 has described the successive colonization of limestone 

conglomerate in Cincinnati. The rock is somewhat resistant to erosionand 

stands out in irregular outcrops on the hillsides of the region. The 

first plants to gain a footing are certain crustaceous lichens, Lccidea sp., 

Pertusaria communis, Staurothele mnbrina, Verritcana muralis and Placo- 

dinin citrinum which occur as patches on the smoother and more exposed 

rock faces. With these were associated small quantities of a moss, Grimmia 

apocarpa. In the second stage of growth Dennatocarpon inimatiun, and, to 

a lesser degree, a gelatinous Omphalaria sp. were the most prominent plants, 

1 

Goeppert 1860. 


2 Salter 1856. 


5 Braun 1917.

394 

ECOLOGY 

but mosses were more in evidence, and the next stage consisted almost 

exclusively of mosses and hepatics with Peltigera canina. A thick layer of 

humus was gradually built 

plants were able to flourish. 

up by these plants on which Phanerogamous 

In tropical countries the first vegetation to settle on bare rocks would 

seem to be blue-green gelatinous algae. Three years after the eruption of 

Krakatoa, dark-green layers of these plants were found by Treub 1 on the 

surface of the pumice and ash, and on the loose stones in the ravines of the 

mountain. It was only at a later stage that lichens appeared. 

b. OUTPOSTS OF VEGETATION. Lichens are the only plants that can 

survive extreme conditions of cold or of heat. They grow in Polar regions 

where no other vegetation could obtain sustenance ; they are to be found 

at great heights on mountains all over the globe ; and, on arid desert rocks 

they persist through long dry seasons, depending almost entirely on night 

dews for the supply of moisture. Here we have true lichen formations in 

the sense of modern ecology. 

1 Treub 1888.

CHAPTER X 


A. LICHENS AS FOOD. 

a. FOOD FOR INSECTS, ETC. Some of the earlier botanists made careful 

observations on the important place occupied by lichens in nature as affording 

food to many small animals. In 1791 Jacques Brez 1 wrote his Flore des 

Insectophyles, and in the list of food-plants he includes seven species of 

lichens. The "insects" that frequented these lichens were species of the 

genera Acarus (mites) and Phalena (moths). A few years later Persoon 2 

noted that lichens formed the main food supply of many insects, slugs, etc. 

Zukal 3 

, quoting from Otto Wilde {Die Pflanzen und Raupen Deutschlands, 

Berlin, 1860), gives a list of caterpillars 

that are known to feed on and 

destroy lichens. 

A very considerable number of small creatures feed eagerly on lichens, 

and traces of their depredations are constantly to be seen in the empty 

fruit discs, and in the cortices eaten away in patches so as to expose the 

white medulla. It has been argued by Zukal 4 that the great formation of 

acid substances in lichens is for shielding them against the attacks of 

animals; Zopf 5 on the contrary insists that these substances afford the plants 

no real protection. He made a series of experiments with snails, feeding 

them with slices of potato smeared with pure lichen acids. Many snails ate 

the slices with great readiness even when covered with bitter acids such as 

cetraric, or with those which are poisonous for other animals such as rhizo- 

carpic and pinastrinic. The only acid they refused was.vulpinic, which is 

said to be poisonous for vertebrates. The crystals of the acids passed 

unchanged through the alimentary canal of the snails, and were found in 

masses in the excreta. They were undissolved, but, enclosed in slime, their 

sharp edges did no damage to the digestive tract. 

Stahl 6 however upholds Zukal's theory of the protective 

function of 

lichen acids against the attacks of small animals. Some few snails, cater- 

pillars, etc., that are omnivorous feeders consume most lichens with impunity, 

and the bitter taste seems to attract rather than repel them ; but many 

others he contends are certainly prevented from eating lichens by the 

presence of the acids. He proved this by soaking portions of the thalli of 

certain bitter species for about twenty-four hours in a one per cent, soda 

solution, which was sufficiently strong to extract the acids. He found that 

1 Brez 1791. 


5 

Zopf 1896. 

3 4 

Zukal 1895, p. 1317 (note). Zukal 1895, p. 1315. 

' 

Stahl 1904.

396 ECONOMIC AND TECHNICAL 

these treated specimens were in most cases preferred to fresh portions that 

had been simply moistened with water. 

Even the omnivorous snail, Helix hortensis, was several times observed 

to touch the fresh thallus and then creep away, while it ate continuously 

the soda-washed portion as soon as it came into contact with it. Calcium 

omnivorous feeders ate 

oxalate, on the other hand, formed no protection ; 

indifferently calcicolous lichens such as Aspicilia 

calcarea and Lecanora 

saxicola, whether treated with soda or not, but would only accept lichens 

with acid contents, such as Parmelia caperata, Evernia prunastri, etc., after 

they had been duly soaked. 

Experiments were also made with wood-lice (Oniscus murarius\ and 

with earwigs (Forficula auricularia), and the result was the same : they 

would only eat bitter lichens after the acids had been extracted by the soda 

method. Stahl therefore concludes that acids must be regarded as eminently 

adapted to protect lichens which otherwise, owing to their slowness of 

growth, would scarcely escape extinction. 

The gelatinous Collemaceae, as also Nostoc, the alga with which these 

are associated, are unharmed by snails, etc., on account of their slippery 

consistency when moist, which prevents the creatures from getting a foothold 

on the thallus. These lichens however do not contain acids, and if, when 

dry, they are reduced to powder and then moistened, they are eagerly eaten 

both by snails and by wood-lice. Peltigera canina, on account of a disagreeable 

odour it acquires on being chewed, is avoided to a certain extent, but 

even so it is frequently found with much of the thallus eaten away. 

Hue 1 in his study of Antarctic lichens, comments on the abundance and 

perfect development of the lichens, especially the crustaceous species, which 

cover every inch of rock surface. He ascribes this to the absence of snails 

and insects which in other regions so seriously interfere with the normal 

and continuous growth of these plants. 

Snails do not eat lichens when they are dry and hard, but on damp or 

dewy nights, and on rainy days, all kinds, both large and small, come out 

of their shells and devour the lichen thalli softened by moisture. Large 

slugs (Limax) have been seen devouring with great satisfaction Pertusaria 

faginea, a bitter crustaceous lichen. The same Limax species eats many 

different lichens, some of them containing very bitter substances. Zopf 2 

observed that Helix cingulata ate ten different lichens, containing as many 

different kinds of acid. 

Other creatures such as mites, wood-lice, and the caterpillars of many 

butterflies live on lichens, though, with the exception of the caterpillars, they 

eat them only when moist. Very frequently the apothecial discs and the 

soredia are taken first as being evidently the choicest portions. All lichens 

1 Hue 1915. 

2 

Zopf 1907.

are, however, not equally palatable. Bitter 1 

LICHENS AS FOOD 397 

observed that the insect Psocus 

(Orthoptera) had a distinct preference for certain species, and restricted its 

attention to them probably because of their chemical constitution. He noted 

that in a large spreading thallus of GrapJiis elegans on holly, irregular bare 

spots appeared, due to the ravages of insects probably Psocus. In other 

places, the thallus alone had been consumed, leaving the rather hard black 

fruits (lirellae) untouched. In time the thallus of Thelotrema lepadinnm, 

also a crustaceous lichen, invaded the naked areas, and surrounded the 

Graphis lirellae. The new comer was not to the taste of the insects and was 

left untouched. 

Fetch 2 

says that lichens form the staple food of Termes monoccros, the 

black termite of Ceylon. These ants really prefer algae, but as the supply 

is limited they fall back on lichens, though they only consume those of 

a particular type, or at a particular stage of development. Those with 

a tough smooth cortex are avoided, preference being given to thalli with a 

loose powdery surface. At the feeding ground the ants congregate on the 

suitable lichens. With their mandibles they scrape off small fragments of 

the thallus which they form into balls, varying in size from i'5 mm. to 2*5 mm. 

in diameter. The workers then convey these to the nests in their mandibles. 

It would seem that they carry about these balls of food, and allow the ants 

busy in the nest to nibble off portions. Lichen balls are not used by termites 

as fungi are, for "gardens." 

Other observations have been made by Paulson and Thompson 3 in their 

study of Epping Forest lichens: "Mites of the family Oribatidae must be 

reckoned among the chief foes of these plants upon which they feed, seeming 

to have a special predilection for the ripe fruits. We have had excellent 

specimens of PJiyscia parietina spoiled by hidden mites of this family, which 

have eaten out the contents of the mature apothecia after the lichens have 

been gathered. One can sometimes see small flocks of the mites browsing 

upon the thallus of tree-dwelling lichens, like cattle in a meadow." The 

Oribatidae, sometimes called beetle-mites, a family of Acarinae, are minute 

creatures familiar to microscopists. They live chiefly on or about mosses, 

for the 

but Michael 4 is of opinion that a large number frequent these plants 

in and about the mosses. In Michael's 

fungi and lichens which grow 

Monograph of British Oribatidae, four species are mentioned as true lichen- 

lovers, Leiosoma palmicinctum found on Peltigera canina and allied species ; 

Cepteus ocellatus and Oribata parmeliae which live on Physciae, the latter 

Saitwertes maculatus 

exclusively on Physcia (Xanthoria) parietina ; and 

which confines itself to lichens by the sea-shore. Another species, Notaspis 

lucoruni, frequents maritime lichens, but it is also found on other substrata; 


2 Fetch 1913. 

* Michael 1884. 

3 Paulson and Thompson 1913.

398 


while Tegeocranus labyrinthicus, though usually a lichen-eating species, lives 

either on mosses or on lichens on walls. Zopf * reckoned twenty-nine species 

of lichens, mostly the larger foliose and fruticose kinds, that were eaten by 

mites. Lesdain 2 in his observations on mite action notes that frequently the 

thallus round the base of the perithecia of Verrucaria sp. was eaten clean 

away, leaving the perithecia solitary and extremely difficult to determine. 

J. A. Wheldon 3 found the eggs of a species of mite, Tetranychus lapidus, 

attached to the fruits of Verrucaria calciseda, Lecidea immersa and L.Metzleri, 

calcicolous lichens of which the thallus not only burrows deep down into 

the limestone, but the fruits form in shallow excavated pits (Fig. 126). The 

\ / 

Fig. 126. i, Tetranychus lapidus, enlarged; i, Verrucaria calciseda with eggs in situ, slightly 

enlarged ; 3 and 4, eggs attached to lichen fruits, much magnified (after Wheldon). 

eggs of this stone mite are found fairly frequently on exposed limestone 

rocks, bare of vegetation, except for a few crustaceous lichens. "There is 

usually a single egg, rarely two, in each pit apparently attached to the old 

lichen apothecium. The eggs are very attractive objects under a lens; they 

measure '5 mm. in diameter, and are disc-like with a central circular depres- 

sion from which numerous ridges radiate to the circumference, like the spokes 

of a wheel. When fresh, they have a white pearly lustre, becoming chalk- 

white when dry and old." Wheldon's observations were made in the Carnforth 

and Silverdale district of West Lancashire. 

1 

Zopf 1907. 

- Lesdain 1910. 

3 Wheldon 1914.


A minute organism, Hymenobolina parasitica 1 

, first described by Zukal 

and doubtfully grouped among the mycetozoa, feeds, in the plasmodium 

stage, on living lichens. The parasitic habit is unlike that of true mycetozoa. 

It has recently been recorded from Aberdeenshire. 

b. INSECT MIMICRY OF LICHENS. Paulson and Thompson 2 

give instances 

of moth caterpillars, which not only feed on lichens, but which take on the 

coloration of the lichens they affect, either in the larval or in the perfect 

moth stage. "One of the most remarkable examples of this protective 

resemblance to lichens is that of the larva of the geometrid moth, Cleora 

/ichenaria,\\\\ich feeds upon foliose lichens growing upon tree-trunks and 

palings, and being of a green-grey hue, and possessed of two little humps 

on many of their body-segments, they so exactly resemble the lichens in 

colour and appearance as to be extremely difficult of detection." Several 

instances are recorded of moths that resemble the lichens on which they 

settle : perfect examples of such similarity are exhibited at the Natural 

History Museum, South Kensington, where Teras literana, Moma orion, and 

other moths are shown at rest on lichen-covered bark from which they can 

hardly be distinguished. 

Another curious instance of suggested mimicry is recorded by G.E. Stone 3 . 

He spotted a number of bodies on the bark of some sickly elms in Massa- 

chusetts. They were about of an inch in diameter " with a dark centre 

and a drab foliaceous margin." They were principally lodged in the crevices 

of the bark and Stone collected them under the impression that they were 

the apothecia of a lichen' most nearly resembling those of Physcia hypoleuca. 

Some of the bodies were even attached to the thallus of a species of Physcia; 

others were on the naked bark and had every appearance of lichen fruits. 

Only closer examination proved their insect nature, and they were identified 

as belonging to a species Gossypina Ulmi, an elm-leaf beetle common in 

Europe where it causes a disease of the tree. It had been imported into 

the United States and had attacked American elms. 

'It is stated by Tutt 4 that the larvae of many of the Psychides (Lepi- 

doptera) live on the lichens of trees and walls, such as Candelaria concolor, 

Xanthoria parietina, Physcia pulvenilenta and Buellia canescens, and that 

their larvae pupate on their feeding grounds. Each species makes a "case" 

peculiar to itself, but those of the lower families are usually covered exter- 

nally with grains of sand, scraps of lichens, etc. The " case " of Narcyria 

inonilifera, for instance, is somewhat raised on a flat base and is obscured 

with particles of sand and yellow lichen, giving the whole a yellow appearance. 

That of Luffia lapidella is roughly conical and is held up at an angle of 30 

to 45 when the larva moves. The "cases" of Bacotia septum are always 

upright; they measure about 5-5 mm. in height and 275 mm. in width and 


- Paulson and Thompson 1913. 

3 Stone 1896. 

4 Tutt 1900, p. 107.

4oo ECONOMIC AND TECHNICAL 

present a hoary appearance from the minute particles of lichen with which 

they are covered, so that the structure is not unlike the podetium of a 

Cladonia. 

c. FOOD FOR THE HIGHER ANIMALS. It has been affirmed, especially 

by Henneguy, that many lichens, if deprived of the bitter principle they 

contain, by soaking in water, or with the addition of sodium or potassium 

carbonate, might be used with advantage as fodder for animals. He cites as 

examples of such, Lobariapulmonaria, Everniaprunastri, Ramalinafraxinea, 

R. farinacea, and R. fastigiata, all of which grow abundantly on trees, and 

owe their nutritive quality to the presence of lichenin, a carbohydrate allied 

to starch. 

Fig. 127. Cladonia rangiferina Web. (S. H , 

Photo.}. 

Cladonia rangiferina (Fig. 127), the well-known "reindeer moss," is, 

however, the lichen of most economic importance, as food for reindeer, 

cattle, etc. It is a social plant and forms dense tufts and swards of slender, 

much branched, hollow stalks of a greenish-grey colour which may reach 

a height of twelve inches or even more; the stalks decay slowly at the base 

as they increase at the apex, so that..,very great length is never attained. 

In normal conditions they neither wither nor die, and growth continues 

indefinitely. It is comparatively rare in the northern or hilly regions of the 

British Isles, and is frequently confused with the somewhat smaller species 

Cl. sylvatica which is very common on our moorlands, a species which Zopf 1 

tel-ls us reindeer absolutely refuse to eat. 

1 

Zopf 1907, p. 372.


The true reindeer moss is abundant in northern countries, more especially 

in forest regions 1 and in valleys between the tundra hills which are more or 

less sheltered from the high winds; it is independent of the substratum and 

flourishes equally on barren sand and on wet turf; but grows especially well 

on soil devastated by fire. For long periods it may be covered with snow 

without injury and the reindeer are accustomed to dig down with horns and 

hoofs in order to reach their favourite food. Though always considered as 

peculiarly " reindeer " 

moss, deer, roebuck and other wild animals, such as 

Lemming 

rats 2 

, feed on it largely during the winter. In some northern 

districts it is collected and stored as fodder for domestic cattle ; hot water 

Fig. 128. Celraria islandica Ach. (S. H., Photo.}. 

is poured over it and it is then mixed with straw and sprinkled with a little 

salt. Johnson 3 has reported that the richness of the milk yielded by the 

small cows of Northern Scandinavia is attributed by some to their feeding 

in great measure on the "reindeer moss." 

When Cladonia rangiferina is scarce, a few other lichens 4 are made use 

of, Alectoria jubata, a brownish-black filamentous tree-lichen being one of 

the most frequent substitutes. Stereocaulon paschale, which grows in large 

dense tufts on the ground in mountainous regions, is also eaten by reindeer 

and other animals; and Iceland moss, Cctraria islandica, is stored up in 

5 

the Icelanders and used as fodder. Willemet reports it 

large quantities by 

as good for horses, oxen, cows and pigs. 

1 Kihlman 1890. 

4 

Lindsay 18*6. 

* Linnaeus 1762. 

5 Willemet 1787. 

3 

Johnson 1861. 

26

402 


It is interesting to recall a discovery of prehistoric remains at the 

Abbey of Schussenried on the Lake of Constance and described by F. Keller 1 : 

under successive beds of peat and crumbly tufa, there was found a layer, 

3 feet thick, containing flints, horns of reindeer and bones of various animals, 

and, along with these, masses of reindeer moss ; a sufficient proof of its 

antiquity as a fodder-plant. 

d. FOOD FOR MAN. Lichens contain no true starch nor cellulose, but the 

lichenin present in the cell-walls of the hyphae has long been utilized as 

a food substance. It is peculiarly abundant in Cetraria islandica (Fig. 128), 

which grows in northern countries, covering great stretches of ground with 

its upright strap-shaped branching fronds of varying shades of brown. In 

more southern lands it is to be found on high hills or on upland moors, but 

in much smaller quantities. Commercial " Iceland moss " is supplied from 

Sweden, Norway or Iceland. In the last-named country the inhabitants 

harvest the lichen preferably from bare stony soil where there is no admixture 

of other vegetation. They revisit the locality at intervals of three years, the 

time required for the lichen to grow to a profitable size ; and they select 

the wet season for the ingathering of the plants as they are more easily 

detached when they are wet. If the weather should be dry, they collect it 

during the night. When gathered it is cleansed from foreign matter and 

washed in water to remove as much as possible of the bitter principle. It 

is then dried and reduced to powder. When required, the powder is put to 

macerate in water for 24 hours, or it is soaked in a weak solution of soda 

or of carbonate of potassium, by which means the bitter cetraric acid is 

nearly all eliminated. When boiled 2 it yields a jelly which forms the basis 

of various light and easily digested soups or of other delicacies prepared 

by boiling in milk, which have been proved to be valuable for dyspeptics or 

sufferers from chest diseases. The northern nations also make the powder 

into bread, porridge or gruel. Johnson 3 states in his account of " Useful 

Plants " that considerable quantities of Iceland moss were formerly em- 

ployed in the manufacture of sea biscuit, and that ship's bread mixed with 

it was said to be less liable to the attacks of weevil than when made from 

wheat flour only. 

An examination of the real food value of the mucilaginous extract from 

"Iceland moss" has been made by several workers. Church 4 states that for 

one part of flesh formers, there are eight parts of heat-givers reckoned as 

starch. Brown 8 isolated the two carbohydrates, lichenin and iso-lichenin. 

The former, a jelly which yields on hydrolysis a large quantity of a reducing 

sugar, dextrose, ferments with yeast and gives no phloroglucin reaction ; 

it is unaffected by digestion and probably does not form glycogen. 

1 Keller 1866. 

4 Church 1880. 

2 Proust 1906. 

5 Brown 1808. 

3 Johnson 1861.


Iso-lichenin is much less abundant and resembles soluble starch, but on 

digestion yields only dextrins no sugar. It may be concluded, judging 

from the chemical nature of the mucilage, from the resistance of its con- 

stituents to digestion and from the small amount present in the jelly, that 

its nutritive value is practically nil 1 . 

It has been stated that " reindeer moss " in times of food scarcity is 

powdered and mixed with "Iceland moss" and rye to make bread in North 

Finland. Johnson confirms this and cites the evidence of a Dr Clarke that: 

" to our surprise we found we might eat of it with as much ease as of the 

heart of a fine lettuce. It tasted like wheat-bran, but after swallowing it, 

there remained in the throat and upon the palate a gentle heat, or sense of 

burning, as if a small quantity of pepper had been mixed with the lichen." 

The Egyptians 2 have used Evernia prunastri, more rarely E. furfuracea, 

in baking. In the eighteenth century fermentative agents such as yeast 

were unknown to them, and these lichens, which were imported from more 

northern lands, were soaked in water for two hours and the solution then 

mixed with the flour to give a much appreciated flavour to the unleavened 

bread. 

In India 3 a species of Parmelia (near to P. perlatd) known in the Telegu 

language as "rathapu" or rock-flower has been used as a food, generally 

prepared as a curry,by the natives in the Bellary district (Madras Presidency), 

and is esteemed as a delicacy. It is also used medicinally. The collecting 

of rathapu is carried on during the hot weather in April and May, and forms 

a profitable business. 

A note has been published by Calkins 4 on the , authority of a correspondent 

in Japan, that large quantities of Endocarpon (Dermatocarpon) miniatum 

(Fig. 56) are collected in the mountains of that country for culinary purposes, 

and largely exported to China as an article of luxury. The local name is 

"iwataka," meaning stone-mushroom. Properly prepared it resembles tripe. 

It is possibly the same lichen under a different name, Gyrophora esculenta, 

which is described by Manabu Miyoshi 5 as of great food value in Japan 

where it is known as "iwatake." It is a greyish-brown leathery "mono- 

phyllous" plant of somewhat circular outline and fairly large size, measuring 

3 to 1 3 cm. across. Fertile specimens are rare, and are smaller than the 

sterile. It grows generally on the steep declivities of damp granitic rocks and 

is common in various districts of Japan, being especially abundant on such 

mountains as Kiso, Nikko, Kimano, etc. The face of the precipices is often 

thickly covered with the lichen growth. The inhabitants collect the plants 

in large quantities. They dry them and send them to the towns, where they 

are sold in all vegetable stores; some are even exported to other countries. 

1 Hutchinson 1916. Forskal 1875, p- 193- 

5 Miyoshi 1893. 

* Watt l89- 

* Calkins 1892. 

262

404 


These lichens are not bitter to the taste, nor are they irritating as are other 

species of the genus. They are on the contrary quite harmless and are much 

relished by the Japanese on account of their agreeable flavour, in spite of 

their being somewhat indigestible. Though only determined scientifically in 

recent times, this edible lichen has long been known, and the risks attending 

its collection have frequently been described in Old Chinese and Japanese 

writings. 

Other species of Gyrophora including G. polyrhiza (Fig. 129) and 

Umbilicaria, black leathery lichens which grow on rocks in northern regions, 

Fig. 129. Gyrophora polyrhiza Koerb. (S.H., Photo, reduced). 

have also been used as food. They are the "Tripe de Roche" or Rock Tripe 

of Arctic regions, a name given to the plants by Canadian fur-hunters. 

They have been eaten by travellers and others in desperate straits for food ; 

but though to a certain extent nutritious, they are bitter and nauseous, and 

cause severe internal irritation if the bitter acids are not first extracted by- 

boiling or soaking. 

Of more historical interest is the desert lichen Lecanora esculenta, 

supposed to be the manna 1 of the Israelites, and still called "bread from 

heaven." Eversmann 2 wrote an account of its occurrence and qualities, and 

fuller information was given by Berkeley 3 : when mixed with meal to a 

third of its weight it is made into bread and eaten by the desert tribes. 

It grows abundantly in North Africa and in many parts of Western Asia, 

on the rocks or on soil. It is 

easily broken off and driven into heaps by the 

wind; and has been reported as covering the soil to a depth of 15 cm. to 

1 See p. 422. 

2 Eversmann 1825. 

3 

Berkeley 1849.


20 cm. with irregular contorted lumps varying in size from a pea to a small 

nut (Fig. 130). Externally these are clear brown or whitish; the interior 

is white, and consists of branching interlaced 

hyphae, with masses of calcium oxalate crystals, 

averaging about 60 per cent, or more of the 

whole substance. 

A still more exhaustive account is given by 

Visiani 1 

, who 

quotes the experience of a certain 

Fig . . I30 

~ 

Lecano a fscuicnta 

General Jussuf, who had tested its value in the Eversm. Loose nodules of the 

Sahara as food for his soldiers. When bread 

was made from the lichen alone it was friable and without consistency ; when 

mixed with a tenth portion of meal it was similar to the soldiers' ordinary 

bread, and had something of the same taste. The General also it gave as 

fodder to the horses, some of them being nourished with the lichen and 

a mixture of barley for three weeks without showing any ill effects. It is 

also said that camels, gazelles and other quadrupeds eat it with advantage, 

though it is in any case a very defective food. 

A remarkable deposit of the lichen occurred in recent times in Mesopotamia 

during a violent storm of hail. After the hail had melted, the ground 

was seen to be covered, and specimens were sent to Errera 2 for examination. 

He identified it as Lecanora esculenta. In his opinion two kinds of manna 

are alluded to in the Bible : in one case (Exodus xvi.) it is the sweet gum 

exuded from the tamarisk that is described; the other kind (Numbers xi.), 

refers to the lichen. He considers that its nutritive value 

he thinks, plainly 

must be very low, and it can only be valued as food in times of famine. 

B. LICHENS AS MEDICINE 

a. ANCIENT REMEDIES. An interesting note has been published by 

Muller-Argau 3 which seems to trace back the medicinal use of lichens to 

a very remote age. He tells us that Dr Schweinfurth, the distinguished 

traveller, who made a journey through the valley of the Nile in 1864, sent 

to him from Cairo a piece of lichen thallus found in a vase along with berries 

of Juniperus excelsa and of Sapindus, with some other undetermined seeds. 

The vase dated from the i8th Dynasty (1700 to 1600 B.C.), and the plants 

contained in it must thus have lain undisturbed over 3000 years. The broken 

pieces of the lichen thallus were fairly well preserved; they were extremely 

soft and yellowish-white and almost entirely decorticate, but on the under 

surfaces there remained a few black patches, which, on microscopical 

examination, enabled Muller to identify them as scraps of Everniafurfuracea. 

This lichen does not grow in Egypt, but it is still sold there along with 

i Visiani 1867. 


3 Muller-Argau 1881, p. 5*6.

406 


Cetraria islandica and some other lichens as foreign drugs. Dr Schweinfurth 

considered his discovery important as proving the use of foreign remedies 

by the ancient Egyptians. 

b. DOCTRINE OF "SIGNATURES." In the fifteenth century A.D. there was 

in the study and treatment of disease a constant attempt to follow the 

guidance of nature. It was believed that Providence had scattered here and 

there on plants "signatures," or resemblances more or less vague to parts 

of the human body, or to the diseases to which man is subject, thus indi- 

cating the appropriate specific. 

Fig- I 3 I - Parmelia saxatilis Ach. (S. H., Photo.). 

Lichens among other plants in which any "signature" could be detected 

or imagined were therefore constantly prescribed : the long filaments of 

Usnea barbata were used to strengthen the hair; Lobaria pulmonaria, the 

true lung-wort, with its pitted reticulate surface (Fig. 72), was marked as a 

suitable remedy for lung troubles Xanthoria ; 

parietina being a yellow lichen 

was supposed to cure jaundice, and Peltigera aphthosa, the thallus of which 

is dotted with small wart-like tubercles 1 

, was recommended for children who 

suffered from the "thrush" eruption. 

1 See p. 138.

LICHENS AS MEDICINE 407 

The doctrine reached the height of absurdity in the extravagant value 

set on a lichen found growing on human skulls, "Muscus cranii humani" 

or "Muscus ex cranio humano." There are a number of lichens that grow 

indifferently on a variety of substances, and not infrequently on bones lying 

in the open. This skull lichen 1 

Parnielia saxatilis , 

( Fig. 131) or some other, 

was supposed to be worth its weight in gold as a cure for epilepsy. 

Parkinson 2 tells us in all confidence "it groweth upon the bare scalps of 

men and women that have lyen long... in former times much accounted of 

because it is rare and hardly gotten, but in our own times much more set 

by, to make the 'Unguentum Sympatheticum' which cureth wounds with- 

out the local application of salves... but as Crollius hath it, it should be 

taken from the sculls of those that have been hanged or executed for 

offences." Ray 3 

says that the same gruesome plant "is celebrated by several 

authors as useful in haemorrhages and is said to be an ingredient of the 

4 

Armarium ,' reported to have been invented by 

. pepper 

famous 'Unguentum 

Paracelsus." Another lost ointment ! 

c. CURE FOR HYDROPHOBIA. Still another lichen to which extraordinary 

virtue was ascribed, was the very common ground species Peltigera canina 

of which was used in the cure of rabies. Dillenius 5 

(Fig. 54), a preparation 

has published in full the prescription 

as " A certain Cure for the Bite of 

a Mad Dog" which was given to him by a very celebrated physician of that 

day, Dr Richard Mead, who had found it effective : 

" Let the patient be blooded at the arm, nine or ten ounces. Take of 

the herb called in Latin Lichen cinereus terrestris, in English Ash-coloured 

ground liverwort, clean'd, dry'd and powder'd half an ounce. Of black 

powder'd two drachms. 

"Mix these well together and divide the Powder into four Doses, one of 

which must be taken every Morning, fasting, for four Mornings successively 

in half a Pint of Cow's Milk warm. After these four Doses are taken, the 

Patient must go into the cold bath, or a cold Spring or River, every Morning 

fasting, for a Month. .He must be dipt all over but not stay in (with his 

head above water) longer than half a minute, if the Water be very cold. 

After this he must go in three Times a Week for a Fortnight longer." 

Lightfoot 6 some , forty years later, refers to this medicine as " the once 

celebrated ' 

Pulvis antilyssus,' much recommended by the great Dr Mead." 

He adds that " it is much to be lamented that the success of this medicine 

has not always answered the expectation. There are instances where the 

application has not prevented the Hydrophobia, and it is very uncertain 

1 From an examination of old figures 

of the Muscus cranii, Arnold (1892, p. 53) has decided that 

several kinds of lichens or hepatics 

are included in this designation. 

* 

2 3 

Parkinson ,640, p. 1313- ^ l686 ' P- "? Am rCUX i;87 ' P' ^ 

6 

5 

Dillenii-s 1741, p. 202. 

Lightfoot 1777, M. p. 846.

4o8 ECONOMIC AND TECHNICAL 

whether it has been at all instrumental in keeping off that disorder." Belief in 

the efficacy of the powder died out before the end of the cerjtury but the echo 

of the famous remedy remains in the name Peltigera canina, the dog lichen. 

d. POPULAR REMEDIES. Lichens with very few exceptions are non- 

poisonous plants. They owed their repute as curative herbs to the presence 

in the thallus of lichenin and of some bitter or astringent substances, which, 

in various ailments, proved of real service to the patient, though they have 

now been discarded in favour of more effective drugs. Some of them, on 

account of their bitter taste, were frequently used as tonics to replace 

Fig. 132. Pertusaria amara Nyl. on bark (S. H., Photo.']. 

quinine in attacks of fever. Several species of Pertusaria, such as the bitter 

P. amara (Fig. 132), and of Cladonia as well as Cetraria islandica (Fig. 128), 

were recommended in cases of intermittent fever; species of Usnea and 

others, as for instance Evernia furfuracea, were used as astringents in 

haemorrhages; others were given for coughs, Cladonia pyxidata (Fig. 69) 

being supposed to be specially valuable in whooping cough. 

One of the most frequently prescribed lichens was the tree lung-wort 

(Lobaria pulmonarid) (Fig. 72). It was first included among medical plants 

by 

Dorstenius 1 

, a Professor at Marburg; he gives a good figure and supplies 

1 Dorstenius 1540.

LICHENS AS MEDICINE 409 

directions for its preparation as a cure for chest complaints. The doctrine 

of "signatures" influenced practitioners in its favour, but it contains lichenin 

which acts as an emollient. In England, it was taken up by the famous 

1 

Dr Culpepper , who, however, believed in astrology even more than in sig- 

" 

natures. He : says it is of great use with many physicians to help the 

diseases of the lungs and for coughs, wheesings and shortness of breath 

which it cureth both in man and beast." He adds that "Jupiter seems to 

own the herb." A century later we find Dr John Hill 12 

, who was a physician 

as well as a naturalist, stating that the great tree lung-wort has been at all 

times famous in diseases of the breast and lungs, but by that time "it was 

not much used owing to change in fashions." 

The only lichen that has stood the test of time and experience as a real 

remedy is Cetraria islandica, and even the " Iceland moss " is now rarely 

prescribed. The first mention in literature of this famous plant occurs in 

Cordus 3 as the Muscus with crisp leaves. Some years later it figures among 

the medicinal plants in Sibbald's 4 Chronicle of the Scottish Flora, and Ray 5 

wrote of it about the same time as being known for its curative and alimentary 

properties. It was Linnaeus 6 

7 

and later , 

Scopoli who it 

, gave the 

important place it held so long in medicine. It has been used with advantage 

in many chronic affections as an emollient and tonic. Cramer 8 in a lengthy 

dissertation gathered together the facts pertaining to its use as a food, 

a medicine and for dyeing, and he gives recipes he had himself prescribed 

with marked success in many different maladies. It has been said that if 

"Iceland moss" accomplished all the good it was alleged to do, it was indeed 

a " Divine gift to man." 

The physiological action of cetrarin (acid principle of the lichen) on 

living creatures has been studied by Kobert 9 and his pupils. It has not any 

poisonous effect when injected into the blood, nor does it work any harm 

when taken into the stomach even of small animals, so that it may be safely 

given to the most delicate patients. Nearly always after small doses peristaltic 

movements in the intestines are induced which indicate that as 

a drug it might be of service in the case of enfeebled organs. In larger 

doses it may cause collapse in animals, but if administered as free cetraric 

acid it passes through the stomach unchanged to become slowly and completely 

dissolved in the intestine. The mucous membrane of the intestine 

of animals that had been treated with an overdose, was found to be richer 

in blood so that it seems as if cetrarin might be of service in chlorosis and 

in assisting digestion. 

Cetrarin has also been proved to be a nerve excitant which might be 

used with advantage in mental maladies. 

1 

Culpepper 1652. 

6 

Linna^s 1737. 

s 

* * 

Hill 1751. Cordus 1561. 

Sibbald 1684. Ray 1686. 

7 

8 

Scopoli 1760. 

Cramer 1880. 

Kobert 1895.

4 io ECONOMIC AND TECHNICAL 

C. LICHENS AS POISONS 

Though the acid substances of lichens are most of them extremely 

irritating when taken internally, very few lichens are poisonous. Keegan 1 

writing on this subject considers this quality of comparative innocuousness 

as a distinctive difference between fungi and lichens and he decides that 

it proves the latter to be higher organisms from a physiological point of 

view: "the colouring matters being true products of deassimilation, whereas 

those of fungi are decomposition or degradation waste products of the 

albuminoids akin to alkaloids." 

The two outstanding exceptions to this general statement are the two 

Alpine species Letharia vulpina and Cetraria pinastri. The former contains 

vulpinic acid in the cortical cells, the crystals of which are lemon-yellow in 

the mass. Cetraria pinastri produces pinastrinic acid in the hyphae of the 

medulla and the crystals are a beautiful orange or golden yellow. 

These lichens, more especially Letharia vulpina, have been used by 

Northern peoples to poison wolves. Dead carcasses are stuffed with 

a mixture of lichen and powdered glass and exposed in the haunts of 

wolves in time of frost. 

2 

Henneguy , who insists on the non-poisonous 

character of all lichens, asserts that the broken glass is the fatal ingredient 

in the mixture, but Kobert 3 

, who has proved the poisonous nature of vul- 

pinic acid, says that the wounds caused by the glass render the internal 

organs extremely sensitive to the action of the lichen. 

Kobert, Neubert 4 and others have recorded the results of experiments 

on living animals with these poisons. They find that Letharia vulpina either 

effect on the mucous membrane. 

powdered or in solution has an exciting 

Elementary organisms treated with a solution of the lichen succumbed 

more quickly than in a solution of the acid as a salt. Kobert concluded 

that vulpinic acid is a poison of protoplasm. 

He further tested the effect of the poison on both cold- and warm-blooded 

animals. Administered as a sodium salt, 4 mg. proved fatal to frogs. The 

effect on warm-blooded animals was similar. A sodium salt, whether 

swallowed or administered as subcutaneous or intravenous injections, was 

poisonous. Cats were the most sensitive hedgehogs the least of all the 

animals that were subjected to the experiments. Volkard's 3 

synthetic pre- 

paration of vulpinic acid gave the same results as the solution directlyextracted 

from the lichens. 

1 

Keegan 1905. 

2 

3 

Henneguy 1883. 

Kobert 1895. 

5 

See p. 228 

4 Neubert 1893.

LICHENS IN INDUSTRY 411 

D. LICHENS USED IN TANNING, BREWING AND DISTILLING 

The astringent property in Cetraria islandica and in Lobaria pulmonaria 

has been made use of in tanning leather. The latter lichen grows commonly 

on oak and could hardly be gathered in sufficient quantity to be of com- 

mercial importance. Like many other lichens it develops very slowly. 

Lobaria pulmonaria has also been used to replace hops in the brewing of 

beer. Gmelin 1 in his journey through Siberia visited a monastery at Ussolka 

where the monks employed it for this purpose. The beer tasted exactly 

like that made with hops, but was more intoxicating. The lichen in that 

country grew on pine-trees. 

Lichens have in more modern times been used in the preparation of 

alcohol. The process of manufacture was discovered by Roy'of Tonnerre, 

early in the nineteenth century, and was described by Leorier 2 . It was 

further improved by Stenberg 3 

, a Professor of Chemistry in Stockholm. 

Roy had worked with Physcia ciliaris, Ramalina fraxinea, R. fastigiata, 

R. farinacea and Usnea florida, but Stenberg and distillers after his time 4 

made more use of Cladonia rangiferina (Fig. 127), Cetraria islandica 

(Fig. 128) and Alectoria jubata. 

By treatment with weak sulphuric or nitric acid the lichenin of the 

thallus is transformed into glucose which on fermentation forms alcohol. 

Stenberg found that 68 per cent, of the weight in Cladonia rangiferina was 

a " 

sugar " from which a good brandy could be prepared : a kilogramme of 

the lichens furnished half a litre of alcohol. The Professor followed up his 

researches by establishing a distillery near Stockholm. His papers contain 

full instructions as to collecting and preparing the plants. Henneguy 5 

writing in 1883, stated that the fabrication of alcohol from lichens was then 

a large and increasing industry in Sweden. The whole industry seems, 

however, to have fallen into disuse very soon : 

Wainio 

6 

, quoting Hellbonv, 

states that the various distilleries were already closed in 1884, because of 

the exhaustion of the lichen in the neighbourhood, and the impossibility of 

obtaining sufficient supplies of such slow-growing plants. 

E. DYEING PROPERTIES OF LICHENS 

a. LICHENS AS DYE-PLANTS. Knowledge as to the dyeing properties 

of lichens dates back to a remote antiquity. It has been generally accepted 

that lichen-colours are indicated by the prophet Ezekiel in his denunciation 

of Tyre: "blue and purple from the Isles of Elishah was that which covered 

thee." Theophrastus describes certain plants as growing in Crete, and being 

1 2 3 * 

Gmelin 1752, p. 425. 

Leorier 1825. Stenterg 1868. Richard r 87 7. 

8 

7 

Henneguy 1883. Wainio 1887, p. 4 Hellbom 1886, 7- 

p. 72. 

,

4 i2 ECONOMIC AND TECHNICAL 

used to dye wool, etc., and Pliny in his Phycos Thalassion is also under- 

stood as referring to the lichen Roccella, "with crisp leaves, used in Crete for 

dyeing garments." 

Information as to the dyeing properties of certain lichens is given in most 

of the books or papers dealing with these plants from the herbals onwards. 

Hoffmann 1 devoted a large part of his Commentatio de vario Lichenum usu 

to the dye-lichens, and, illustrating his work, are a series of small rectangular 

coloured blocks representing samples of woollen cloth dyed with different 

lichens. There are seventy-seven of these samples with the colour names 

used by French dyers. 

An important treatise on the subject translated into French was also 

2 contributed . by Westring He desired to draw attention to the tinctorial 

properties of lichens other than the Roccellae which do not grow in Sweden. 

The Swedes, he states, already used four to six lichens as dye-plants, but 

only for one colour. He demonstrated by his improved methods that other 

colours and of finer tint could be obtained. He describes the best methods 

both of extraction and of dyeing, and then follows with an account of the 

different lichens likely to be of service. The treatise was subsequently 

published at greater length in Swedish 3 with twenty-four very fine coloured 

illustrations of the lichens used, and with sample blocks of the colours to be 

obtained. 

b. THE ORCHIL LICHEN, ROCCELLA. The value of Roccella as a dye- 

plant had been lost sight of until it was accidentally rediscovered, early in 

the fourteenth century, by a Florentine merchant called Federigo. He intro- 

duced its use into Florence, and as he retained the industry in his own hands 

he made a large fortune, and founded the family of the Orcellarii, called 

later the Rucellarii or Rucellai, hence the botanical name, Roccella. The 

product was called orseille for which the English name is orchil or archil. 

Another origin suggested for orchil is the Spanish name of the plant, 

Orcigilia. There are a number of different species that vary in the amount 

of dye-product. Most of them grow on rocks by the sea-side in crowded 

bluish-grey or whitish tufts of strap-shaped or rounded stiff narrow fronds 

varying in length up to about six inches or more. The main supply of 

"weeds" came from the Levant until the fifteenth century when supplies 

were obtained from the Canaries (long considered to produce the best 

varieties), Cape Verd and the African coasts. The geographical distribution 

of the Roccellae is very wide: they grow on warm sea-coasts all over the 

globe, more particularly in Angola, the Cape, Mozambique, Madagascar, in 

Asia, in Australia, and in Chili and Peru. 

Zopf 4 has proved the existence of two different colouring substances 

among the Roccellas : in R. fuciformis (Fig. 57) and R. fucoides (both 

1 Hoffmann 1787. 

2 

Westring 1792 and 1793. 

3 Westring 1805-1809. 

4 Zopf 1907.

LICHENS AS DYE-PLANTS 413 

British species), in R. Montagnei and R.peruensis the acid present is erythrin ; 

in R. tinctoria, R. portentosa and R. sinuensis it is lecanoric acid. In 

R, tinctoria (Fig. 133), according to Ronceray 1 

in the gonidial layer and the soredia but 

is absent from the cortex and centre. In 

R. portentosa it is abundant in the cortex 

and central layer, while scarcely to be 

detected in the gonidial layer, and it is 

wanting altogether in the soredia. In R. 

Montagnei it is chiefly found in the cortex 

and the gonidial layer, and is absent from 

the soredia and from the medulla. 

c. PURPLE DYES: ORCHIL, CUDBEAR 

AND LITMUS. Orseille or orchil is formed 

not only from erythrin and lecanoric acid 

(orseillic acid), but also from erythrinic, 

gyrophoric, evernic and ramalic acids'2 and 

may be obtained from any lichen containing 

these substances. By the action of 

ammonia the acids are split up into orcin 

and carbonic acid. In time, under the 

influence of ammonia and the oxygen of 

the air 3 

, 

orcin becomes orcein which is the 

colouring principle of orchil ; 

the perfecting 

of the process may take a month. The dye 

is used for animal fibres such as wool and 

silk ; it has no effect on cotton. 

, the acid is located chiefly 

There are several different preparations 

on the market, chiefly obtained from Franee 

'33- Koccella tinctoria Ach. 

the Cape 

From 

orchil or orseille in the form of a solution, cudbear (persio of 

of Good Hope. 

and Holland ; 

Germany) almost the same, but manufactured into a violet-reddish powder, 

and litmus (tournesol of France) which is prepared in a slightly different 

manner. At one time the lichen, broken into small pieces, was soaked in 

urine; a fermentation process was set up, then lime and potash with an 

admixture of alum were added. The mass of material when ready was 

pressed into cubes and dried in the air. Commercial litmus contains three 

substances, erythrolein, erythrolitmin and azolitmin ; the last named, which 

is the true litmus, is a dark brown amorphous powder soluble in water, and 

forming a blue solution with alkalies. 

1 

2 

Ronceray 1904. 

Zopf 1907. 

3 Zahlbruckner (1905, p. 109) quotes from Czapek a statement that orchil fermentation is brought 

about by an obligate aerobic bacillus.

4 i4 


An aqueous solution of litmus when exactly neutralized by 

an acid is 

violet coloured ; it becomes red with the smallest trace of free acid, or blue 

with free alkali. Litmus paper is prepared by steeping specially prepared 

unsized paper in the dye solution. It is as a ready and sensitive indicator 

of acidity or alkalinity that litmus is of so much value. According to Zopf 1 

it is also used as a blueing agent in washing and as a colouring of wine. 

Litmus is chiefly manufactured in Holland. Still another substance somewhat 

differently prepared from the same lichens is sold as French purple, 

a more brilliant and durable colour than orchil. 

Fig. 134. Lecanora tartarea Ach. (S. H., Photo.). 

d. OTHER ORCHIL LICHENS. Though species of Roccella rank first in 

importance as dye-plants, purple and blue colours are obtained, as indicated 

above, from other very different lichens. Lindsay 2 extracted orchil from 

about twenty species. Those most in use in northern countries are on the 

whole less rich in colouring substances ; they are : Umbilicaria pustulata, 

species of Gyrophora, Parmelia and Pertusaria, and above all Lecanora 

tartarea (Fig. 134). The last named, one of the hardiest and most abundant 

1 

Zopf 1907, p. 393. 

2 

Lindsay 1855.


of rock- or soil-lichens, is chiefly used in Scotland and Sweden (hence the 

name " Swedish moss") to furnish a red or crimson dye. In Scotland all 

dye-lichens are called "crottles," but the term "cudbear" was given to 

Lecanora tartarea (either the lichen or the dye-product); it was acquired 

from a corrupt pronunciation of the Christian name of Dr Cuthbert Gordon, 

a chemist, who, according 

to Bohler 1 

, 

obtained a patent for his process of 

producing the dye, or who first employed it on a great scale in Glasgow. 

Johnson- remarks that the colour yielded by cudbear, if well prepared, is 

a fine, clear, but not very bright purple. It is, he alleges, not permanent. 

Like other orchil substances it is without effect on cotton or linen. 

f. PREPARATION OF ORCHIL. A general mode of treatment of dye- 

lichens recommended by Lauder Lindsay 3 for home production of orchil, 

cudbear and litmus is as follows : 

1. Careful washing, drying and cleansing to separate earthy and other 

impurities. 

2. Pulverization into a coarse or fine pulp with water. 

3. Repeated addition of ammoniacal liquor of a certain strength, obtain- 

able from several sources (e.g* putrid urine, gas liquor, etc.). 

4. Frequent stirring of the fermenting mass so as to ensure full exposure 

of every part thereof to the action of atmospheric oxygen. 

5. Addition of alkalies in some cases (e.g. potash or soda), to heighten 

or modify colour ; and of chalk, gypsum and other substances to impart 

consistence. 

/. BROWN AND YELLOW DYES. The extracting of these colours from 

lichens is also a very old industry. Linnaeus found during his journey to 

undertaken when he was quite a young man, that the women in 

Lappland 4 

, 

the northern countries made use of a brown lichen for dyeing which is 

evidently Parmelia ompJialodes (Fig. 135). He describes it as a "rich 

Lichenoides of a brown stercoraceous colour," and he has stated that it grew 

in such abundance in the Island of Aland, that every stone was covered, 

especially near the sea. In the Plantae tinctoriae* there is a record of six 

other lichens used for dyeing : Lichen Roccella, L. tartareus, L. saxatilis, 

L. juniperinus, L. parietinus and L. candelarius. The value of Lichen oni- 

phalodes was also emphasized by Lightfoot ; 

the women of Scotland evidently 

appreciated its dyeing properties as much as other northern peoples. 

A series of memoirs on the utility of lichens written by Willemet", 

Amoreux and Hoffmann, and jointly published at Lyons towards the end 

of the eighteenth century, represents the views as to the economic value 

of lichens held by scientific botanists of that time. All of them cite the 

1 Bohler 1835, N. 10. 


2 Johnson 1861. 

3 Lindsay 1855. 

6 Willemet etc. 1787. 

4 Linnaeus 1711.

4i6 


various dye-species, and Hoffmann, as already stated, gives illustrations of 

colours that can be obtained. It has been once and again affirmed that 

Parmelia saxatilis yields a red colour, but Zopf 1 denies this. It contains 

saxatillic acid which is colourless when extracted but on boiling gives 

a clear reddish-yellow to reddish-brown solution which dyes wool and silk 

directly without the aid of a mordant. Zopf 1 observed the process of dyeing 

Fig. 135. Parmelia oviphalodes Ach. (S. H., Photo."]. 

followed in South Tyrol : a layer of the lichen was placed in a cooking pot, 

above this a layer of the material to be dyed, then lichen and again the 

material until the pot was filled. .It was covered with water and boiled 

three to four hours, resulting in a beautiful rust-brown and peculiarly fast dye. 

Reddish- or rust-brown dye is also obtained from Haematomma ventosum 

and H. coccineum, a yellow-brown from Parmelia conspersa (salazinic acid), 

and other shades of brown from Parmelia perlata, P. physodes, Lobaria pul- 

monaria and Cetraria islandica. 

Yellow lichens in general furnish yellow dyes, as for instance Xanthoria 

parietina which gives either brown or yellow according to treatment and 

Cetraria juniperina which forms a beautiful yellow colouring substance on 

* 

Zopf 1907.


boiling. Teloschistes flavicans and Letharia vulpina yield very similar yellow 

dyes, and from Lecanom parella (Fig. 39), Pertusaria melaleuca and Usnea 

barbata yellow colours have been obtained. Candelariella vitellina and 

Xanthoria lychnea both contain yellow colouring agents and have been 

employed by the Swedes for dyeing the candles used in religious ceremonies. 

g. COLLECTING OF DYE-LICHENS. Lauder Lindsay 1 made exhaustive 

studies of dye-lichens both in the field and in the laboratory, and recorded 

results he obtained from the micro-chemical examination of 540 different 

specimens. He sought to revive and encourage the use of their beautiful 

colour products among country people; he has given the following practical 

hints to collectors: 

1. That crustaceous dwarf pale-coloured species growing on rocks, and 

especially on sea-coasts, are most likely to yield red and purple dyes similar 

to orchil, cudbear or litmus; while on the other hand the largest, most handsome 

foliaceous or fruticose species are least likely. 

2. That the colour of the thallus is no indication of colorific power (in 

orchil lichens), inasmuch as the red or purple colouring substances are the 

result of chemical action on crystalline colorific "principles" previously 

devoid of colour. 

3. That alterations in physical characters, chemical composition and 

consequently in dyeing properties are very liable to be produced by modi- 

fication in the following external circumstances : 

(i) Degree of moisture. 

(ii) Degree of heat. 

(iii) Degree of exposure to light and air. 

(iv) Climate. 

(v) Elevation above the sea. 

(vi) Habitat ; nature of basis of support. 

(vii) Age. 

(viii) Seasons and atmospheric vicissitudes, etc. 

August has been recommended as the best month for collecting dyelichens 

: i.e. just after the season of greatest light and heat when the 

accumulation of acids will be at its maximum. 

Some of the acids found useful in dyeing occur in the thalli of a large 

number of lichens, many of which are too scantily developed to be of any 

economic value. Thus salazinic acid which gives the effective yellow-brown 

dye in Parmelia conspersa was found by Zopf in 13 species and varieties. 

It has since been located by Lettau 2 in 72 different lichens, many of them, 

however, with poorly developed or scanty thalli, so that no technical use 

can be made of them. 

S. L. 

1 

Lindsay 1855. 

2 Lettau 1914. 

2 7

4 i8 ECONOMIC AND TECHNICAL 

h. LICHEN COLOURS AND SPECTRUM CHARACTERS. In a comparative 

study of vegetable colouring substances, Sorby 1 extracted yellow colouring 

matters from various plants distinguished by certain spectrum characters. 

He called them the "lichenoxanthine group" because, as he explains, "these 

xanthines occur in a more marked manner in lichens than in plants having 

true leaves and fronds. Orange lichenoxanthine he found in Peltigera 

canina, Platysma glaucum, etc., when growing well exposed to the sun. 

Lichenoxanthine he obtained from the fungus Clavaria fusiformis; it 

was difficult to separate from orange lichenoxanthine. Yet another, which 

he terms yellow lichenoxanthine, he obtained most readily from Physcia 

(Xantfiorid) parietina. The solutions of these substances vary according to 

Sorby in giving a slightly different kind of spectrum. He did not experiment 

on their dyeing properties. 

F. LICHENS IN PERFUMERY 

a. LICHENS AS PERFUMES. There are a few lichens that find a place 

in Gerard's 2 Herball and that are praised by him as being serviceable to 

man. Among others he writes of a " Moss that partakes of the bark of 

which it is engendered. It is to be used in compositions which serve for 

sweet perfumes and that take away wearisomeness." At a much later date 

we find Amoreux 3 

recording the fact that Lichen {Evernia) prunastri, 

known as " Mousse de Chene," was used as a perfume plant. 

Though lichens are not parasitic, the idea that they owed something of 

their quality to the substratum was firmly held by the old herbalists. It 

appears again and again in the descriptions of medicinal lichens, and still 

persists in this matter of perfumes. Hue 4 states in some notes to a larger 

work, that French perfumers extract an excellent perfume from Evernia 

prunastri (Fig. 59) known as " Mousse des Chenes " 

(Oak moss), and it ap- 

pears that the plants which grow on oak contain more perfume than those 

which live on other trees. The collectors often gather along with Evernia 

prunastri other species such as Ramalina calicaris and R. fraxinea, but these 

.possess little if any scent. A still finer perfume is extracted 5 from Lobaria 

pulnionaria called " moss from the base of the oaks," but as it is a rarer 

lichen than Evernia it is less used. Most of the Stictaceae, to which family 

Lobaria belongs, have a somewhat disagreeable odour, but this one forms 

a remarkable exception, which can be tested by macerating the thallus and 

soaking it in spirit : it will then be found to exhale a pleasant and very 

persistent scent. These lichens are not, however, used alone; they are combined 

with other substances in the composition of much appreciated perfumes. 

The thallus possesses also the power of retaining scent and, for this reason, 

lichens frequently form an ingredient of potpourri. 

1 

Sorby 1873. 

2 Gerard 1597. 

3 Amoreux 1787. 

* Hue 1889. 

5 Hue 1900.

LICHENS IN PERFUMERY 419 

b. LICHENS AS HAIR-POWDER. In the days of white-powdered hair, 

use was occasionally made of Ramalina calicaris which was ground down 

and substituted for the starch that was more commonly employed. 

In older books on lichenology constant reference is made to a hair- 

powder called " Pulvis Cyprius " or " Cyprus powder " and very celebrated 

in the seventeenth century. It was believed to beautify and cleanse the hair 

by removing scurf, etc. Evernia prunastri was one of the chief ingredients 

of the powder, but it might be replaced by P/iyscia ciliaris or by Usnea. 

The virtue of the lichens lay in their capacity to absorb and retain perfume. 

The powder was for long manufactured at Montpellier and was a valuable 

monopoly. Its composition was kept secret, but Bauhin 1 

(J.) published an 

account of the ingredients and how to mix them. Under the title " Pulvis 

Cyprius Pretiosius" a more detailed recipe of the famous powder was given 

2 

by Zwelser 

include both Evernia and 

, a Palatine medical doctor. The lichen employed in his pjeparation, 

as in Bauhin's, is Usnea, but that may 

Physcia as they are all tree plants. He gives elaborate directions as to the 

cleaning of the lichen from all impurities it is to be beaten with a stick, 

washed repeatedly with limpid and pure water, placed in a linen cloth and 

dried in the sun till it is completely bleached and deprived of all odour and 

taste. 

When well dried it was placed in a basket in alternate layers with freshly 

gathered, entire flowers of roses and jasmine (or flowers of orange and citrus 

when possible). The whole was compressed by a heavy weight, and each 

day the flowers were renewed until the "Usnea" was thoroughly impregnated 

with a very fragrant odour. It was then reduced to a fine powder and ready 

for other ingredients. To each pound should be added : 

li oz. powdered root of white Iris. 

i^- oz. of Cyperus (a sedge). 

I scruple or half drachm of musk reduced to a pulp with fragrant spirit 

of roses. 

\ drachm of ambergris dissolved in a scruple of genuine oil of roses, or 

oil of jasmine or oranges as may be preferred. 

Zwelser adds : 

"This most fragrant royal powder when sprinkled on the head invigorates 

by its remarkably pleasant odour; by its astringency and it dryness removes 

all impurities, and, since it operates with no viscosity nor sticks firmly either 

to skin or hair, it is easily removed from the hair of the head." 

1 Bauhin 1650, p. 88. 

2 Zwelser 1672. 

272

420 


G. SOME MINOR USES OF LICHENS 

The possibility of extracting gum or mucilage from lichens was demon 

strated by the Russian 1 

scientist, Professor Georgi and later , 

by Amoreux 2 

the method employed being successive boiling of the plants. The largei 

foliose or fruticose forms were specially recommended. 

At a later date, during the Napoleonic wars, the "ingenious Lore 

Dundonald 3 

," of great fame as an inventor, published 

an account of the 

extraction process and of the application of the gum to calico-printing 

staining and manufacture of paper, dressing and stiffening silks. Lore 

Dundonald's aim was to replace the gum Senegal, then a monopoly of the 

French, who were in possession of the Settlement of Senegambia. He toolout 

a patent for his invention, but whether the gum was successfully usec 

is not recorded. 

According to Henneguy 4 

, lichen mucilage, as a substitute for gum arabic 

has been used at Lyons with advantage in the fabrication of dyed materials 

1 

Georgi 1779. 

2 Amoreux 1787. 

3 Dundonald 1801. 

4 Henneguy 1883.

APPENDIX 

POSTSCRIPT TO CHAPTER VII 1 

IN a remarkable paper on The Symbiosis of Lichens-, Dr A. Henry Church 

has presented a new and striking view of the origin and development of 

lichens: he has sought to link them up with other classes of vegetation that, 

in the great transmigration, passed from sea to land. As we know from his 

TJialassiopJiyta* and the subaerial transmigration, he holds that primeval 

algae of advanced form and structure were left exposed on dry land 

by the gradually receding waters, and those that successfully adapted 

themselves to the changed conditions formed the basis of the land flora. 

A certain number of the algae lost their surface tissues containing chlorophyll 

and they had perforce to secure from other organic sources the necessary 

: carbohydrates they adopted a heterotrophic existence as saprophytic or 

parasitic fungi. Fungi are a backward race (deteriorated according to 

Dr Church) as regards their soma, but in number, distribution and variety 

of spore-production, they are eminently successful plants. 

Lichens are similarly regarded by Dr Church as derived from stranded 

contemporaneous types of marine algae crustaceous, foliose and fruticose, 

that had also lost their chlorophyll, but by taking into association green 

algal units of a lower grade they established a vicarious photosynthesis. 

" 

as the alga-lichen-fungus left the sea, so it 

But, to quote his own words 4 

, 

remained : it might deteriorate, but it certainly never advanced, once the 

sea factors which produced it were eliminated, it simply stopped along 

these lines." 

And again 5 : 

" Lichens thus present an interesting case of an algal race 

deteriorating along the lines of a heterotrophic existence, yet arrested, as it 

were, on the somatic down-grade, by the adoption of intrusive algal units 

of lower degree to subserve photosynthesis (much in the manner of the 

marine worm Convoluted). Thus arrested, they have been enabled to retain 

more definite expression of more deeply inherent factors of sea-weed habit 

and construction than any other race of fungi ; though closely paralleled 

by such types as Xylaria (Ascomycete) and Clavaria (Basidiomycete), 

which have followed the full fungus progression as holosaprophytic on 

decaying plant residues." 

Dr Church's theory is of vivid interest and might be convincing were 

there no possibility and no proof of advance within the symbiotic plant, but 

See p. 302. 

2 Jourti. Bot. LVIII. pp. 213-9 > * 62 ~7' '9 70 ' 

4 Church I'M lift. 

* Bot - Memoirs * 3> Oxford, 1919. 

5 

Journ. Bot. I.e.

422 

APPENDIX 

in numbers of crustaceous thalli, there is evident, by normal or abnormal 1 

development, the first advance to the formation of rudimentary squamules, 

a condition diagnosed as subsquamulose. "Deterioration" of the lichen 

plant when it occurs owing to unfavourable conditions is a reversion to 

the leprose early stage of the association ; there is no evidence of reversion 

from fruticose or foliose to squamulose. A glance at the table of lichen phyla 2 

shows progression again and again from the crustaceous forms onwards. 

In such a phylum as Physciaceae (with colourless polarilocular spores) there 

is a clear example of a closely connected series; the different types of 

thallus crustaceous, squamulose, foliose and fruticose are all represented 

and form a natural sequence, being well delimited by the unusual form of 

the spore and by the presence of parietin in thallus or apothecium. 

That there has been development seems absolutely certain, and that 

along the lines sketched in the chapter on phylogeny. Progress has been 

mainly in the thallus, but there has also been change and advance in the 

reproductive organs, more especially in the spores which in several families 

reach a size and septation unparalleled in fungi. That association with green 

algal cells stimulated the fungus to new development is the view taken of 

the lichen plant and emphasized in the present volume. But it seems more 

in accordance with the polyphyletic origin and recurring parallel development 

in the phyla that association began at the elementary crustaceous stage, and 

that the lichen soma was gradually evolved within what is after all a very 

limited and simple structure. 

ADDENDUM 

FOOT-NOTE TO PAGE 404 

E. M. Holmes 3 has published recently an account of a substance which seems in some 

respects to answer to the description of manna (Exodus xvi. ; Numbers xi.) more nearly 

than the generally accepted Lecanora escuhnta. The information is quoted from Swann's 

book: Fighting the slave-hunters in Central Africa. The author writes (p. 116): "I was 

shown a curious white substance similar to porridge. It was found early in the morning 

before the sun rose. On examination it was found to possess all the characteristics of the 

manna of the Israelites. In appearance it resembled coriander seed, was white in 

colour like hoar frost, sweet to the taste, melted in the sun and if kept over night was full 

of worms in the morning. It required to be baked if you intended to keep it for any length 

of time. It looked as if it was deposited on the ground in the night." The writer has 

suggested that "the substance might be mushroom spawn as, on the spot where it melted 

tiny fungi sprung up the next night." Swann's statement has been confirmed by 

Dr Wareham, a medical missionary from the same district, who states, however, that it is 

of rare occurrence. 

1 See p. 271 ante. 2 See p. 302 ante. 

3 Chemist and Druggist, xcn. pp. 25-26, 1920; Bot. Abstracts, N. 903, p. 135, 1920.

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Wiesner, J. Untersuchungen iiber den Lichtgenuss der Pflanzen, etc. Sitzungsb. K. Akad. 

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Abrothallus De Not., 267 

A. Cetrariae Kotte, 264 

A. oxysporus Tul., 263 

A. Peyritschii Kotte, 264 

A. Smithii Tul., 263 

Acanlhothedum Wain., 322 

Acarinae, 271, 397 

Acarospora Massal., 183, 331, 390 

A. chlorophana Massal., 374, 375, 390 

A. glaucocarpa Koerb. , 176 

A. Heppii Koerb., 377 

A. pruinosa (Sm.), 377 

A. 'smara^dula Massal. , 388, 393 

A.xanthophana (Nyl.), 242 

Acarosporaceae, 310, 331 

Acarus, 395 

Acharius, i, 10, 123, 120, 133, 141, 149, 150, 

185, 192, 304 

Acolium, S. F. Gray, 277 

Acrocordia gemmata Koerb., 152 (Fig. 906) 

Acroscyphus, Lev., 320 

A. sphaerophoroides Lev., 289 

Actlnoplaca Miill.-Arg., 327 

Acton, xix, 57 

Adanson, 9 

Aesculus, 253 

Agardh, C- A., xx, 21 

Agyrium flavescens Rehm, 266 

Aigret, 125, 371, 384 

Alectoria Ach., 85, 94, 101, 103, 200, 257, 300, 

340, 346, 350, 352 

A. implexa Nyl., 227 

A.jnbata Ach ,3, in, 401, 411 

A. nigncans Nyl., 346, 389 

A. ochroleuca Ach., 227, 389 

A. thrausta Ach., 105 (Fig. 60) 

Alectoriaceae, 339 

Allarthonia Nyl., 321 

AUarthothelium Wain., 321 

Allescher, 201 

Almquist, 262 

Ambergris, 419 

Amoreux, 10, 407, 415, 418, 420 

Amphidinm Nyl., 335 

Aviphiloma Koerb., 325 

Anaboena Bory, 41 

Anaptychia Koerb., 341 (see Physcia) 

Anapyrenium Miill.-Arg., 315 

Anema Nyl., 333, 373 

Angiocarpeae, 156 

Anthoceros L., 41 

Anthracothecium Massal., 316, 350 

Anzia Stiz., 90, 299, 339 

A. colpoctes Stiz., 90 

A. japonica Miill.-Arg., 90 

Archer, 28 

Arctomia Th. Fr , 334 

Argopsislh. Fr., 105, 135, 297, 330 

INDEX 

Arnold, 18, 261, 342, 343, 364, 368, 370, 407 

Arnoldea minutula Born., 190 (Fig. 108) 

Arnott, Walker, 15 

Artari, 39, 42 

Arthonia Ach., 158, 203, 278, 305, 321, 343, 361 

A. astroidea Ach., 202 

A. cinnabarina Wallr. (see A. gregarid], 349 

A. dispersa Nyl., 365 

A. gregaria Koerb., 247, 248 

A. lecideella Nyl., 365 

A. pruinosa Ach., 145 

A. rattiata Ach., 78, 365 

A. subvarians Nyl., 262 

Arthoniaceae, 59, 278, 309, 321 

Arthoniopsis Miill.-Arg., 321 

Arlhopyrenia Massal., 30, 316 

A.fallax Am., 365 

A. halizoa A. L. Sm., 383 

A. haloJytes Oliv., 383 

A. leptotera A. L. Sm., 383 

A. macrospora Fink, 365 

A. marina A. L. Sm., 383 

A. punctiformis Arn., 346, 365 

A. quinqueseptata Fink, 365 

Arthotheliopsis Wain., 327 

Artholheliuin Massal., 321 

Ascolichens, 272, 273, 281, 308, 311 

Ascomycetes xix, 178 et passim 

Ascophanus carneus Boud. 1 80 

, 

Aspergillus Micheli, 220 

Aspicilia Massal., 133, 136, 140 (see Lecanora} 

A. alroviolacea (Flot.) Hue, 158 

A.fiavida (Hepp), 248 

Aspidoferae, 9 

Aspidopyrenium Wr ain., 314 

Aspidothelium Wain., 314 

Aster istion Leight., 337 

Asterosporum Mull.-Arg., 316 

Asterothyrium Miill.-Arg., 327 

Astrotheliaceae, 309, 317, 352 

Astrothelium Trev. ,317 

Athalami, 305 

Aulaxina Fee, 322 

Azolla Laur., , 

41 

Babikoff, 138 

Babington, 18, 350 

Bachmann, E., 35, 75, 76, 215, 216, 235, 247, 

347, 393 

Bachmann, Freda, 162, 179, 181, 186 

Bacidia, De Not., 329 

B. acdinis (Flot.), 248 

B . Beckhausii Koerb., 262 

B. flavovirescens Anzi, 280 

B. fuscoriibella Arn., 249, 365 

B. inundata Koerb., 372, 373, 377, 391, 392 

B. muscorum Mudd, 248, 368, 370, 377 

B. rubella Massal., 365

Bacotia septum, 399 

Baeotnyces Pers., 123, 293, 294, 330 

B. paeminosus Krempelh., 55 

B. placophyllus Ach. , 293, 368 

B. roseus Pers., 123, 167, 195, 218, 247, 362, 

367, 368, 369 

B. rufus, DC., 123, 167, 177, 218, 237, 240, 

362, 368, 369 

Baranetzky, 24 

Bary, de, 24, 31, 187, 209, 213 

Bauhin, J., 419 

Bauhin, K., 3 

Baur, 51, 115, 118, 124, 161, 165, 167, i68i 169, 

170, 172, 173, 174, 176, 177, 180, 181, 185, 

255 

Beckmann, 230, 257 

Beechey, 15 

Beetle-mites, 397 

Beijerinck, 39, 220 

Beilstein, 211 

Belonia Koerb., 316 

Berg, 211 

Berkeley, 252, 404 

Berzelius, 210 

Betula nana L., 95 

Bialosuknia, 57 

Biatora Koerb., 158, 279, 293 (see also Lecidea), 

39' 

Biatorella Th. Fr., 331 

B. dnerea Th. Fr., 375 

B. pruinosa Mudd, 217 (Fig. 119) 

B, resinae Th. Fr., 355 

B. simplex Br. and Rostr., 217 (Fig. 118) 

B. testudinea Massal., 375 

Biatorina Massal., 245, 291 

B. Bonteillei Arn., 363 

B. chalybeia Mudd, 386 

B. coeruleonigricans A. L. Sm., 367 

B. globulosa Koerb., 378 

B. lentictilaris Koerb., 383 

B. prasina Syd., 33, 61 

B. (denigrata) synothea Koerb., 33, 204 

Bilimbia, aromatica Jatta, 349 

B. incana A. L. Sm., 343 

B. microcarpa Th. Fr., 262 

B. obscurata Th. Fr., 262 

B. sabulosa Massal., 370 

B. sphaeroides Koerb., 385 

Bioret, 320 

Birger, see Nilson 

Bitter, 64, 79, 94, 97, 131, 140, 143, 147, 148, 

149, 151, 176, 240, 242, 253, 257, 261, 267, 

337, 397 

Blackman, 206 

Blackman and Welsford, 179 

Blastenia Th. Fr., 340 

Blastodesmia Massal., 316 

Bohler, 415 

Bombyliospora De Not., 329 

Bonnier, 29, 36, 47, 65, 189, 232, 253 

Bornet, 27, 28, 32, 36, 61, 78, 136, 189 

Borrer, 12, 14 

Borrera, see Physcia 

Borzi, 28, 161, 164 

Botrydina vulgaris Breb. , xix, 57 

Botrydium pyriforme Kiitz., 45 

Bottaria Massal., 317 

S. L. 

INDEX 449 

Bouilhac, 42, 140 

Braconnot, 214 

Brandt, 103, 130 

Braun, Fr., 354 

Braun, L., 393 

Brefeld, 189, 207 

Brez, 395 

Brooks, F. T., 64, 179 

Brown, E. W., 402 

Brown, W. H., 168 

Bryopogon, see Oropogon 

Bryum L., 392 

Buchet, 90 

Buddie, 4 

Buellia, De Not., 263, 280, 291, 302, 308, 341, 

347 

B. aethalea Th. Fr., 261 

B. atrata Mudd, 245, 375 

B. canescens De Not., 80, 366, 377, 380, 399, 

B. colludens Tuck., 382, 386 

B. coradna Koerb., 375 

B. discolor Koerb., 388 

B. leptocline Koerb., 374 

B. myriocarpa Mudd, 50, 346, 366, 369 

B. parasema Th. Fr., 365, 367, 377 

B. Parmeliarum Oliv., 263 

B. pnnftiformis, 50, 202, 207 (Fig. 118) 

B. ryssolea A. L. Sm., 380, 382 (Fig. 125) 

B. stellulata Mudd, 382, 388 

B. triphragmia Th. Fr., 390 

B. turgescens Tuck., 367 

B. verruculosa Mudd, 261 

Buelliaceae, 311, 341 

Buxbaum, 6, 10 

Buxus sempervirens L., 353 

Cactus, 325, 353 

Calenia Miill.-Arg., 338 

Caliciaceae, 62, 115, 175, 189, 244, 288, 309, 

3 '9. 353, 366 

Calicium De Not., 184, 201, 277, 319, 361 

C. arenariitm Nyl. , 376 

C. corynellum Ach., 376 

C. hyferelltim Ach., 349, 365 

C. partednum Ach., 202, 367 

C. Irachelinum Ach., 196, 202, 204 

Calkins, 348, 403 

see Cal/opisma, Platodium 

Calluna Salisb., 95, 355 

Caloplaca Th. Fr. (see P/aeodium), 340 

C. aitrantia, var. callopisma Stein., 190 

C. gilvella (Nyl.), 2 76 C. inteneniens Miill.-Arg., 276 

C. pyraceat\L. Fr., 34, 388 

Caloplacaceae, 311, 340 

Calothricopsis Wain., 333 

Calyddium Stirt., 289, 320 

C. cuneatum Stirt., 350 

Camellia L., 269 

Camerarius, i 

Camillea Fr., 276 

Campylidium ,191 

Campylothelium Miill.-Arg., 317 

Candelaria Massal., 339 

C. concolor Wain., 365, 388, 399 

Candelariella Miill.-Arg., 338 

C. cerinella A. Zahlbr., 390

450 

Candelariella vitellina Miill.-Arg., 233, 237, 

369, 377,.393. 417 

Capnodium Mont., 179 

Carpinus Tournef., 240 

Carrington, 12 

Carroll, 19 

Cassini, 21 

Catillaria Th. Fr. (see Biatorind), 329 

C. Hochstetteri Koerb., 375 

Celidiaceae, 265 

Cdliditim stictarum Tul., 267 

Cenomyce Th. Fr., 295 

Cephaleuros Kunze (see Mycoided), 59, 288 

Cephaloidei, 303 

Cepteus ocellatus, 397 

Cerania S. F. Gray, 340 

C. vermiadaris S. F. Gray, 194, 387 

Cetraria Ach., 84, 94, 200, 210, 213, 225, 241, 

264, 299, 346, 350, 357, 358, 370, 388, 399 

C. aculeata Fr., 211, 241, 262, 299, 300, 355, 

369,384,385,386, 387 

C. caperata Wain., 264 

C. crispa Lamy, 387, 388 

C. ctuullata Ach., 201, 244, 389 

C. diffusa A. L. Sm., 366 

C. islandica Ach., 2, 94, 128, 195 (Fig. 112), 

210, 212, 221, 227, 231, 241, 338, 355, 387, 

401 (Fig. 128), 406, 408, 409, 411, 416 

C. juniperina Ach., 201, 246, 416 

C. Lanreri Kremp., 364 

C. nivalis Ach., 201, . 

210, 389 

C. pinastri S. F. Gray, 145, 246, 410 

C. tristis, see Parmelia 

Chaenotheca Th. Fr., 201, 319 

C. chrysocephala Th. Fr., 265, 277, 288 

Chalice-Moss, 3 

Chambers, 43 

Chasmariae, 295 

Chevalier, 13 

Chiodecton Miill.-Arg., 276, 320, 323, 351, 364 

Chiodectonaceae, 59, 278, 309, 323 

Chlorella Beij., 56" 

Ch. Cladoniae Chod., 56 

Ch.faginea Wille, 56 (Fig. 23 A) 

Ch. lichina Chod., 56 

Ch. miniata Wille, 56 (Fig. 23 A) 

Ch. viscosa Chod., 56 

Ch.vnlgaris Beyer., 42, 56 

Chlorococcus (? Chlorococcum Fr.), 24 

Chlorophyceae, xix, 51, 55-60, 61, 272, 324 

Chodat, 28, 30, 43, 44, 55, 115, 329 

Chroococcaceae, 25 

Chroococais Naeg., 24, 52, 82, 136, 153, 284, 

3 11 - 33 2 > 373 

Ch. giganteus West, 52 (Fig. 16) 

Ch. Schizodermaticus West, 52 (Fig. 16) 

Ch. turgidns Naeg., 52 (Fig. 16), 136 

Chroolepus Ag., see Trentepohlia 

C. ebeneus Ag., 22 

Chrysothricaceae, 57, 310, 325 

Chrysothrix Mont., 325, 353 

C. noli tangere Mont., 325 

Church, A. Henry, 42 1 

Church, A. Herbert, 402 

Cicinnobolus Ehrenb. , 261 

Cinchona L., 364 

INDEX 

Cinchona cordaminea Humb., 364 

C. cordifolia Mutis, 364 

C. oblongifolia Mutis, 364 

Claassen, 34 

Cladina Leight, 112, 122, 253, 292 

Cladonia Hill, 9, 13, 23, 38, 44, 55, 56, 80, 81, 

95, 104, 106, 172, 213, 237, 241, 242, 257, 

262, 329, 344, 346, 347, 355, 358, 372, 375, 

3 8 5. 39V 39 9.' 4 8 

Cl. agariciformis Wulf., 368 

Cl. aggregata Ach., 120 

Cl. alcicomis Floerk., 385, 386 

Cl. alpestris Rabenh., 125, 211, 349, 369 

Cl. alpicola Wain., 122 

1 1 8 

Cl. amaurocrea Schaer. , 

Cl. bjllidiflora Schaer., 1 19 

Cl. botrytes Willd., 173 

Cl. caespiticia Floerk., 115, 124, 294, 296 

Cl. cariosa Spreng., 113, 120, 295, 296,368 

Cl. cartilaginea Miill.-Arg., 122 

Cl. ceratophylla Spreng., 122 

Cl. cervicornis Schaer., 113, 120, 122, 243, 

384, 387 

Cl. coca/era Willd., 113, 118,368,369,370,387 

Cl. cristatdla Tuck., 367, 369 

Cl. decorticata Spreng., 172 (Fig. 98) 

Cl. deformis Hoffm., 226 

Cl. degenerans Floerk., 114, 117, 124 

Cl. destncta Nyl., 387 

Cl. digitata Hoffm., 113, 122, 371 

Cl. divaricata Meng. and Goepp. , 355 

Cl. enautia f. dllatala Wain., 112 

Cl. endiviaefolia Fr., 384 

Cl.Jimbriata Fr., 51, 117, 120, 295 296, 349, 

367, 368, 370, 377; Subsp.yw/a Nyl., 119, 

369 

Cl. flabelliformis Wain., 371 

Cl. Floerkeana Fr., 173,296, 362, 370 

Cl. foliacea Willd., 112, 113, 120, 122, 240, 

295, 296 

Cl.furcata Schrad., 117 (Fig. 70), 118, 124, 

194 (Fig. 109), 212, 295, 297, 355, 368, 369, 

377, 386 

Cl. gracilis Hoffm., 115 (Fig. 68), 122, 124, 

210, 297, 367, 369, 387 

Cl. leptophylla Floerk., 295, 296 

Cl. macilenta Hoffm., 362, 366, 367, 369, 378 

Cl. miniata Mey., 112, 122 

Cl. nana Wain., 112 

Cl. Neo-Zelandica^Nxm., 112 

Cl.papillaria Hoffm., 195, 296, 344 

Cl.pityrea Floerk., 255, 366 

Cl. pungens Floerk. (see Cl. rangifortnis) 

Cl. pycnoclada Nyl., 345 

Cl. pyzidata Hoffm., 2, 44, no, lit (Fig. 66), 

113, 114, 117 (Fig. 69), 118, 120, 124, 172, 

227, 295, 346, 349, 362, 366, 368, 370, 371, 

377. 408 

Cl. racemosa Hoffm., 387 

Cl. rangiferina Web., 56, 95, 117, 119, 120, 

210, 211, 215, 227, 231, 237, 238, 253, 267, 

293, 297, 349' 355. 357. 3^9. 386, 388, 400, 

, 4IX 

Cl. rangiformis Hoffm., 271, 295, 366, 368, 386 

Cl. retepora Fr., 117, 120 (Fig. 71), 231, 351 

Cl. rosea Ludw., 354 

Cl. solida Wain., 114

INDEX 

Cladonia sqiiamosa Hoffm., 113, 115 (Fig. 67), 

118, 210, 243, 295, 366, 368 

Cl. sylvatica Hoffm., 95, 112, 117, 119, 271, 

349, 366, 368, 369, 385, 400 

Cl. syinphicarpia Tuck., 367 

Cl. tophacea Hill, 8 

Cl. tiirgida Hoffm., 369 

Cl. uncialis Web. , 112, 120, 369, 387, 389 

Cl. -verticillaris Fr. , 122 

Cl. verticillata Floerk., 114, 119, 120, 124, 

349' 36/. 369 

Cladoniaceae, 135, 292, 310, 329, 366, 370 

Cladoniodei, 306 

Cladophora Kiitz., 35, 59, 188 

C. glomerala Kiitz., 58 (Fig. 30) 

Cladophoraceae, 59 

Clathrhiae, 117, 120 

Clathroporina Miill.-Arg., 316 

C/ausae, 295 

Clai'aria Vaill., 421 

Cleora lichenaria, 399 

Cocciferae, 295 

Coccobotrys Chod., 30, 40, 56, 315 

C. Vei-rucariae Chod., 57 (Fig. 24) 

Coccocarpia Pers., 335 

C. tnolybdaea Pers., 61 

C.pellita Miill.-Arg., 166 

Coccomyxa Schmidle, 56 

C. Solorinae croceae Chod., 56 

C. Solorinae saccatae Chod. , 56 

C. 

sitbcllipsoidea Acton, 57 (Fig. 25) 

Coccotrema Miill.-Arg., 316 

Coenogoniaceae, 59, 291, 310, 328 

Cocnogoniitm Ehrenb. , 23, 35,69, 182, 246, 291, 

3 2X > 35' 

C. ebeneum A. L. Sm., 22 (Fig. 3), 34, 59, 

328, 350, 352, 363 

C. implexum Nyl., 352 

C. Linkii Ehrenb., 213 

Coenothalami, 303 

Coleochaete Breb., 178 

Collema Wigg-, 6, 9, 21, 23, 25, 30, 48. 69, 87, 

132, 165, 173, 200, 230, 284, 305, 334, 367, 

392 

C. reranoides Borr., 385 

C. cheileum Ach., 161 

C. crispum Ach., 161, 180 

C. flacciditm Ach., 365 

C. fitiviatile Sm., 392 

C. granulatum Ach., 368 

C. granuliferum Nyl., 69, 232, 243 

C. Hildenbrandii Garov., 202 (see Leptogium) 

C. liinostnn Ach., xx, 21, 349 

C. microphyllum Ach., 160 (Fig. 91), 

161 

(Fig. 92), 202 

C. iiigrescens Ach., 20 (Fig. 2), 101, 243, 245. 

364 

C plicatile, 409 

C.pulposum Ach., 24, 162, 179, 186, 202, 266, 

368, 385 

C. pustiilatiun Ach., 373 

C.pycnocarpum Nyl., 365 

C. tenax Sm., 368 

Collemaceae, 27, 53, 69, 160, 241, 244, 266, 

284, 306, 310, 334, 364, 384, 396 

Cot'le modes Fink, 162 

Collemodiuw, see Leptogium 

Collemopsidiitni Nyl., 3**, 174 

Collybia, Qu61., 105 

Colonna, 3 

Combea De Not., 83 

Conida Massal., 265, 267 

C. mbescens, Arn., 265 

Conidella urceolata Elenk., 265 

Coniocarpi, 307 

Coniocarpineae, 267, 273, 274, 

3'9 

276, 288. 309. 

Coniocarpon DC., ^05 

Coniocybe Ach., 277, 319, 366 

C'. 

fnrfuracea Ach., 746, 376 

Conotrema Tuck., 326 

C. urceolatum Tuck., 343 

Convolnta roscoffensis, 40 

Cora Fr., 53, 246, 281, 311. 342, }H2 

C. Pavonia Fr., 88, 152 (Figs. 86, 87) 

Coralloidcs, 5, 6, 7, 303 

Corda, 200 

Cordus, 409 

Cordyceps Fr., 261 

Corella Wain., 153, 311, 34 342, 35* 

C. brasiliensis Wain., 15. '54 

Coriscium Wain., 285, 288, 319 

Cornicularia (Cetraria) Schreb., 388 

C. ochroleiua Ach., 355 

C. siibpitbescens Goepp.. 355 

C. siiicinea Goepp., 355 

Corylns Tournef., 240 

Cramer, 409 

Croall, 19 

Crocynia Nyl., 325 

C. gossypina Nyl., 325 

C. laimginosa Hue, 325, 373 

Crombie, xxi, 7, 18, 19, 197, 260, 262, 264, 306, 

36i 

Crottles, 415 

Criteria Fr., 73 

Cryptothecia Stirton, 331 

Cryptothele Nyl., 333 

Cudbear, 413, 415 

Culpepper, 409 

Cunningham, 35, 269 

Cuppe-Moss, 3 

Cupthongs, 9 

Curnow, 19 

1 Cutting, 80 

Cyanophili, 308, 310 

Cyanophyceae, 309 

C. Bachinannianttm Fink, 162 

; see Myxophyceae 

Cycas L., 40 

Cyclocarpineae, 273, 279, 290, 309, 314 

Cyperus, 419 

Cypheliaceae, 309, 320 

Cyphelitim Th. Fr., 276, 277, 288, 320 

Cyphella aeriigitiasffus Karst., 191 

Cystofocctts Chod., 55. 56 

C. Cladoniae fimbriatae Chofl., ;6 

C. Cladoniae pixidatae Chod., 56 (Fig. 56) 

Cystococciis Naeg., 24, 26, 28, 34, 115, 219 

C. humifola Naeg.. 24, 27, 40, 55 

Cystocoleus Thwaites, 23 

Cytospora Ehrenb., 204 

Czapek, 211, 413 

Dacantpia Massal., 315 

292

452 

Dactylina Nyl., 340 

D. arctica Nyl., 339, 346 

Dangeard, 185 

Danilov, 37 

Darbishire, 18, 26, 51, 64, 77, 86, 90, 92, 101, 

103, no, 130, 147, 148, 166, 167, 171, 175, 

180, 181, 253, 256, 299, 324, 342, 346, 347, 

377. 3 8 9 

Darbishire and Fischer-Benzon, 307 

Darbishirella A. Zahlbr., 324 

Davies, 12, 14 

Dawson, 178 

De Candolle, 12 

Deckenbach, 59 

Deer, 401 

Delise, 13, 126 

Dendrographa Darbish., 324 

D. leucophaea Darbish., 103, 213 

Dermatiscum Nyl., 331 

Dermatocarpaceae, 309, 314 

Dermatocarpon Eschw., 80, 81, 276, 288, 315 

D. aquaticum A. Zahlbr., 391, 392 

D. cinereum Th. Fr., 368 

D. hepaticum Th. Fr., 368, 388 

D. lachneum A. L. Sm., 88, 368 

D. miniatum Th. Fr., 56, 96 (Fig. 56), 173 

(Fig- 99) 185, 241, 261, 373, 391, 392,403 

Desfontaines, 10 

Diatoms, 220 

Dichodium Nyl., 334 

Dickson, 9 

Dictyographa Miill.-Arg., 322 

Dictyonema A. Zahlbr., 54, 153, 311, 342, 352 

Didymellq Sacc., 276 

Didymosphaeria pulposi Zopf, 266 

Dillenius, xx, i, 6, 155, 192, 262, 304, 407 

Dioscorides, 2 

Diplogramma Miill.-Arg., 322 

Diplopodon, 270 

Diploschistaceae, 310, 326 

Diploschistes Norm., 326 

4. 43> 4'8, 419 

Everniopsis Nyl., 339, 340 

Eversman, 404 

Famintzin, 24 

Farriolla Norm., 319 

Faull, 178 

Fee, 13, 15, 184, 187, 192, 364 

Fink, Bruce, xx, 242, 254, 

368, 369, 373, 389, 391 

Fischer, 308 

Fitting, 36 

Fitzpatrick, 

348, 358, 365, 367, 

181 

Flagey, 373, 389 

Florideae, 160, 177, 273 

Fldrke, 12, 13, 133 

Flotow, 23, J92 

Fontinalis L., 391 

Forficula auricularia, 396 

Forskal, 403 "43 

Forssell 

> 63, 65, 133, 136, 163, 175, 282, 373

Forssellia A. Zahlbr., 284, 333, 373 

Forster, 12, 14 

Fossil Lichens, 353-355 

' 

Frank, 31, 62, 78 

Fraser, 1 78 

French, xxiii 

Friedrich, 75, 233, 269, -270 

Fries, E., 13, 22, 149, 364 

Fries, Th. M., 17, 18, 133, 

342 

Fncus L., 281 

F. spiralis L., 383 

Fuisting, 30, 159, 173 

138, 152, 192, 163, 

Fiinfstiick, 18/19, 61, 75, 76, 161, 169, 170, 

171, 175, 181, 216, 218, 219, 224, 342 

Gage, 14 

Gallic, 95, 242 

Gargeaune, 45 

Gasterolichens, 308 

Gautier, 213 

Geisleria Nitschke, 314 

G. sychnogonioides Nitschke, 370 

Georgi, 10, 420 

Geosiphon Wettst., 45 

Gerard, John, 3, 418" 

Gibelli, 200 

Gilson, 209 

Gleditsch, 269 

Gloeocapsa Kiitz., 23, 32, 55, 61, 68, 136, 195, 

232, 284, 292, 332, 373 

G. magma Kiitz., 52 (Fig. 17), 60, 136 

G. polydermatica Kiitz., 53 

Gloeocystis Naeg., 33, 57 (Fig. 28), 61, 133, 318 

Gloeolichens, 175, 282, 284, 373, 389 

Glossodium Nyl., 330 

G. aversiim Nyl., 294 

Gltick, 198 

Glyphis Fee, 276, 323 

Glypholecia Nyl., 331 

Gmelin, J. F., 152 

Gmelin, J. G., 411 

Gnomonia erythrostoma Auersw., 178 

Goeppert, 354, 393 

Goeppert and Menge, 354 

Gomphillus Nyl., 293, 330 

Gongrosira Kiitz., xxi 

Gongylia Koerb., 314 

G. viridis A. L. Sm., 368, 388 

Gonohymenia Stein., 333 

Gonothecium Wain., 31, 327 

Gordon, Cuthbert, 415 

Gossypina Uhnt, 399 

Grammophori, 307 

Graphidaceae, 59, 158, 309, 321, 351, 352, 364 

Graphideae, 13, 17, 27, 34, 62, 78, 79, 172, 348, 

349 35L 353- 364 

: 

Graphidineae, 273, 278, 289, 309, 320, 365 

Graphina Miill.-Arg., 322 

Graphis Adans., 9, 211', 321, 322, 343, 349, 351, 

355> 36 *> 3 6 4 

G. clegans Ach., 30, 158 (Fig. 89), 172, 180, 

397 

G. scripta Ach., 50, 349, 354, 365, 366 

G. scripta succinea Goepp., 355 

Gray, J. E., 12, 305 

Crete Herball, 2 

INDEX 453 

Greville, 12 

Grimbel, 250 

Grimmia pulvinata Sm., 393 

G. apocarpa Hedw., 393 

Guembel, 392 

Guerin-Varry, 210 

Guillermond, 167 

Gunnera L., 31, 41 

Gyalecta Ach., 191, 318 

G. cttpularis Schaer., 244 

G. Flotoi'ii Koerb., 244 

G. geoica Ach., 254 

G. rtibra Massal., 249 

Gyalectaceae, 54, 59, 69, 310, 327 

Gyalolechia Massal., 201 

G. sHbsimiHs (Th. Fr.) Darb., 378 

Gymnocarpeae, 156, 308, 318 

Gymnoderma Nyl., 330 

G. coccocarpurn Nyl., 293 

Gymnographa Mull.-Arg., 322 

Gyrophora Ach., 88, 96, 184, 200, 227, 231, 241, 

249, 268, 304, 331, 346, 350, 376, 390, 393, 

4'4. 

G. cylindrica Ach., 176, 184 (Fig. 103), 375, 

387 

G. erosa Ach., 330, 387 

G. esculenta Miyosh., 403 

G. flocculosa Turn, and Borr., 375 

G. murina Ach., 94 

G.polyphylla Hook., 387 

G. polyrhiza Koerb., 94, 349, 404 (Fig. 119) 

G. proboscidea Ach., 192, 346, 375 

G. spodochroa Ach., 94 

G. tonefacta Cromb., 375, 387 

G. vellea Ach., 74, 1 76 

Gyrophoraceae, 291, 310, 330 

Gyrostomum Fr., 326 

Haberlandt, 106, 188 

Haematomma Massal., 230, 236, 338 

H. coccineum Koerb., 214, 223, 26 

H. elatinum Koerb., 201 

H. ventosum Massal., 214, 225, 241, 251, 298, 

375, 37.6, 388, 393 

Hagenia filtaris, 24 

Haller, 7, 126 

Halopyrenula Miill.-Arg., 318 

Halsey, 14 

Hamlet and Plowright, 213 

Haniiand, 63 

Harper, 167, 178, 181, 188 

Harpidium Koerb., 298, 338 

H. rutilans Koerb., 298 

Harriman, 14 

Hassea A. Zahlbr., 319 

Hedlund, 32, 61, 204, 245 

Hedwig, 142, 156, 184, 192 

Helix hortfttsis, 396 

H. cingulata, 396 

Hellbom, 350, 411 

HelmmthocarpoH Fee, 322 

Henneguy, 410, 411, 420 

Heppia Naeg., 81, 175, 285, 335, 348, 351, 389 

H. DepreauxiilucV.., 368 

H. Guepini Nyl., 80, 88, 96 

H. virescens Nyl., 368 

Heppiaceae, 54, 285, 310

454 

Herberger, 221 

Herissey, 213 

Herre, 230, 253, 349 

Hesse, 12, 221, 224 

Heterocarpon Mlill.-Arg., 315' 

Heterodea Nyl., 339 

H. MullertNyl., 128, 299, 339, 350 

Heterogenei, 303 

Heteromyces Miill.-Arg., 293, 330 

Heufleria Trev., 317 

Hicks, 14. 

Hildenbrandtia Nardo, 73 

Hill, Sir John, 8, 409 

Hoffmann, 10, 154, 412, 415 

Hofmann, 261 

Holl, 19 

Holle, 14, 46, 187 

Holmes, 19, 422 

Homogenei, 303 

Homopsella Nyl., 334 

Homothalami, 305 

Homothecium Mont., 334 

Hooker, 12, 15, 149 

Hornschuch, xx, 156 

How, 3 

Howe, Heber, 85, 224, 348 

Hudson, 7, 9, 303 

Hue, ii, 16, 18, 33, 57, 63, 69, 73, 82, 85, 103, 

133, '35. 136, 140, 188, 262, 283, 315, 325, 

339. 34> 342, 347, 348, 360, 396, 418 

Hulth, 215 

Hutchins, 14 

Hutchinson, 403 

Hydrothyria Russ., 336 

H. venosa Russ., 97, 175, 233, 286, 348, 390 

Hymenobolina parasitica Zuk. , 267, 399 

Hymenolichens, xix, 54, 152-154, 273, 281, 308, 

3".335, 342 

Hymenomycetes, xix, 153 et passim 

Hyphomycetes, xix, 191 

Hypnum L., 392 

H. cupressiforme L., 385 

Hypogymnia Nyl., 94, 176 

Hypoxylon Bull., 12 

Hysteriaceae, 273, 307 

Hysterium Tode, 12 

Iceland Moss, 210, 401 et passim 

Icmadophila Massal., 166, 338 

/. aeruginosa Mudd, see I. ericetorum 

I. ericetorum A. Zahlbr., 196, 244, 370 

Illosporium carneum Fr., 268 

Ingaderia Darbish., 324 

Iris, white, 419 

Isidium Ach., 149 

'/. corallinum Ach., 149 

/. Westringii Ach., 149 

Istvanffi, 202, 206 

Itzigsohn, 17, 23, 24, 193 

Jaczewski, 353 

Jasmine, oil of, 419 

Jatta, 129 

Jenmania Wacht., 333, 352 

Jennings, Vaughan, 60 

Jesuit's bark, 10 

John, 250 

INDEX 

Johnson, C. P., 401, 402 

Johnson, W., 19 

Johow, 153 

fonaspis Th. Fr. , 328 

Joshua, 19 

Jumelle, 230, 238 

Kajanus (Nilson), 151 

Karschia Koerb., 280 

K. destructans Tobl., 265 

K. lignyota Sacc., 280 

Keeble, 4 i 

Keegan, 224, 410 

Keiszler, 201 

Keller, 402 

Kerner and Oliver, 215 

Kieffer, 371 

Kienitz-Gerloff, 51 

Kihlman, 237, 358, 388, 401 

Knop, 213, 247 

Knop and Schnederman, 221 

Knowles, 224, 249, 379, 384, 391 

Kobert, 409, 410 

Koelreuter, 155 

Koerber, 14, 123, 142, 188, 305 

Koerberia Massal., 334 

Kotte, 264 

Krabbe, 63, 113, 114, 119, 122, 123, 124, 143, 

147, 162, 170, 172, 174, 176, 177, 253 

Kratzmann, 214 

Krempelhuber, i, 55, 244, 364 

Kupfer, 261 

Kutzing, 22 

Laboulbenia Mont, and Robin, 178 

Laboulbeniaceae, 178, 274 

Lachnea scutellata Gill., 168 

L. stercorea Gill., 178 

Lacour, 211 

Lang, 76, 216, 235 

Larbalestier, 19 

Laubert, 206 

Laudatea Joh., 154 

Laurera Reichenb., 317 

Lecanactidaceae, 310, 325 

Lecanactis Eschw., 204, 325 

Lecania Massal., 136, 338 

L. candicans A. Zahlbr., 80 (Fig. 43) 

L. cyrtella Oliv. , 377 

L. erysibe Mudd, 377 

L. holophaea A. L. Sm., 350 

Lecaniella Wain., 327 

Lecanora Ach., 78, 88, 200, 298, 305, 338, 347, 

349- 351, 353, 364, 365, 372, 39 

L. aquatica Koerb., 391 

L. aspidophora f. errabunda Hue, 262 

L. atra Ach., 63, 225, 249, 375, 380, 382 (Fig. 

125), 384, 386, 393 

L. atriseda Nyl., 261 

L. atroflava, see Placodium 

L. aurella (Hoffm.), 262 

L. badia Ach., 79, 375, 386 

L. caesiocinerea Nyl., 218, 384 

L. calcarea Somm., 218 (Fig. 120), 373, 396 

L. campestris B. de Lesd., 361, 384 

L, cenisia Ach., 375 

L. cinerea Somm., 229, 349, 375

Lecanora dtrina Ach., see Placodium 

L. coilocarpa Nyl. , 30 

L.crassa Ach., 79, 81,201, 2 18,367, 368, 373,389 

L. crenulata Hook., 361, 377 

L. Dicksonii Nyl., 250, 375 

L. dispersa Nyl., 261, 369, 377, 384 

L. ejffusa Ach., 204 

L. epanora Ach., 246 

L. epibryon Ach., 378, 389 

L. epulotica Nyl., 392 

L. esculenta Eversm., 21 1, 257, 265, 298, 389, 

404 (Fig. 130), 422 

L. exigna, see Rinodina 

L.ferrnginea Nyl., 30 

L. galactina Ach., 254, 

384. 386 

262, 360, 369, 377, 

L. gelida Ach., 135, 

375 

136, 137 (Fig. 77), 140, 

L. gibbosa Nyl., 375, 384, 386 

L, glaucoma Ach., see L. sordida 

var. corrugata Nyl., 84 (Fig. 46) 

L. Hageni Ach., 366, 367, 369, 377, 383 

L. hypnorum Ach., see Psoroma 

L. lacustris Th. Fr., 233, 250, 391, 392 

L. lentigera Ach., 81, 90, 298, 367 

L. muralis Schaer., 242 

L. ochracea Nyl., 373 

L. pallescens Mudd, 213' 

L. pallida Schaer., 78 

L.parella Ach., 72, 375, 382, 384, 417 

/,. peliocypha Nyl., 375 

L. picea Nyl., 374 

L.piniperda Koerb., 204 

L. polytropa Schaer., 237, 376, 394 

L. prosechoides Nyl., 383, 384 

L. rubina Wain., 390 

L. ragosa Nyl., 366 

L. Samiuci VSyl., 204 

L. saxicola Ach., 79, 80, 81, 233, 252, 349, 

369, 384, 386, 393, 396 

Z. simplex Nyl. (see Biatorella], 75, 77, 382 

Z. smaragdula Nyl., 382 

Z. sophodes Ach., 30; see Rinodina 

L. sordida Th. Fr., 194, 236, 261, 374, 375, 

380, 382 

L. squainulosa Nyl., 374 

L. sitbfusca Ach., 22, 30, 49, 65 (Fig. 34), 70 

Fj g- 88 )' l64. '66, 167, 168, 

(F'g- 57). W ( 

2 3 6 > 347' 3 6 5> 3 66 

L. sulphured Ach., 226, 238, 376, 384 

L, tartarea Ach., 57, 147. 183 (Fig. 102), 224, 

225, 227, 237, 262, 346, 358, 359, 371, 375. 

387, 389, 414 (Fig. 134) 

L. umbrina Massal., 377, 385 

L. upsaliensis Nyl., 387 

L. urbana Nyl., 361 

L. varia Ach., 227, 346, 360, 36?, 362, 366, 

367. 377 

L. ventosa, see Haematonuna 

L. verntcosa Laur., 378 

L. xantholyta Nyl., 373 

Lecanoraceae, 136, 311, 337, 353 

Lecanorales, 297 

Leddea Ach., 78, 184, 261, 279, 292, 304, 308, 

328, 346, 347, 349, 351, 353. 3 64, 3^5, 372, 

373, 385,. 39 

L. aglaea Somm., 375 

INDEX 455 

Leddea albocoerulescens Ach., 392 

L. alpestris Somm., 387 

L. arctica Somm., 387 

L. aromatica (see ftilimbia) 

L. atrofusca Nyl., 248, 387 

L. auriculata Th. Fr., 375 

L. Berengeriana Th. Fr-.'^Sj 

L. coarctata Nyl., 247 

L. 

coeruleonigricans Schaer., 37} 

L. colludeus Nyl., 3*84 ; see Bui-Ilia 

L. confluens Ach., 375, 388 

f. oxydata Leight., 250 

L. consentiens Nyl., 134, 135 

L. contigna Fr., 375, 376, 388, 392 

v&i.jlavicunda Nyl., 250 

L. crustiilata Koerb., 369' 

L. (Bilimbia) cuprea Somm., 387 

L. cupreiformis Nyl., 387 

L. dedpiens Ach., 291, 367, 368 

L. dccolorans Floerk, see L. granulosa 

L. demissa Th. Fr. , 369, 387 

/,. diduccns Nyl., 375 

L. enterolenca Nyl., 164, 168, 365 

L.fumosa Ach., 159 

L.fuscoatra Ach., 200 (Fig. 114), 375 

L. gelatinosa Floerk., 368 

Z. granulosa Schaer., 218, 237, 269, 291, 36: 

369. 37, 377 

Z. grisella Floerk., 243 

Z. helrola Th. Fr., 245 

L. herbidnla Nyl., xxi 

L. iltita Nyl., 136 

L. iinmena Ach., 217 (Fig. 117), 398 

L. inserena Nyl., 375 

L. insularis Nyl., 236, 261 

Z. irregiilaris Fee, 192 

L. Kochiana Hepp, 375 

L. lapicida Ach., 375 

L. lavata Nyl., 384 

L. limosa Ach., 387 

L. lucida Ach., 246, 376 

L. lurida Ach., 79, 195, 241, 367 

Z. mesotropa Nyl., 375 

L. Metzlen"T\\. Fr., 398 

Z. nigroclavata Nyl., 384 

Z. ostreata Schaer., 79, 145, 291, 366 

L. pallida Th. Fr., 135 

L.panaeola Ach., 134, 135, 136, 375 

/,. parasema Ach., 183 (Fig. 101), 366 

L. pelobolrya Somm., 135, 136 

Z. phylliscocarpa Nyl., 31 

Z. phyllocaris Wain., 31, 327 

Z. plana Nyl., 375 

Z. platycarpa Ach., 375 

Z. pycnocarpa Koerb., 375 

Z. quernea Ach., 236, 349, 386 

Z. rivulosa Ach., 374, 375, 376 

Z. sanguinaria Ach., 187 (Fig. 105), 248 

Z. sanguineoatra Ach., 370 

Z. steilitlata Tayl., 376 

Z. sulphurella Hedl., 242 

Z. sylvicola Flot., 372 

Z. testacea Ach., 195 (Fig. in) 

Z. tricolor Nyl. (Biatorina Grijfithii), 361 

Z. tumida Massal., 375 

Z. uliginosa Ach., 254, 291, 370, 385, 387 

Z. wrnalis Ach., 66 (Fig. 35)

456 

Lecideaceae, 135, 241, 279, 291, 298, 310, 327, 

328, 341, 346, 353 

Lecideales, 290, 308 

Leciophysma Th. Fr., 334 

Leighton, 16, 17, 18, 19, 134, 306, 342, 353, 388 

Leiosoma palmicinctum, 397 

Lemming rats, 401 

Lemmopsis A. Zahlbr., 334 

Lenzites Fr., 261, 371 

Leorier, 41 1 

Lepidocollema Wain., 81, 336 

Lepidoptera, 399 

Lepolichen Trevis., 318 

L. coccophora Hue, 57, 318 

L. granulatus Miill.-Arg., 318 

Lepra Hall., 143 

L. viridis Humb., 23 

Lepraria Ach., 143, 237, 305 

L. botryoides, xx 

L. chlorina, 376 

Leprieur, 15 

Leprocollema Wain., 285, 354 

Leproloma Nyl., 325 

Leptodendriscum Wain., 284, 332 

Leptogidium Nyl., 284, 332, 350 

L. dendriscum Nyl., 332 

Leptogium S. F. Gray, 69, 84, 87, 232, 285, 335, 

37 

L. Burgessii Mont., 245 

L. byssinum Nyl., 368 

L. Hildenbrandii Nyl., 364 

L. lacerum S. F. Gray, 243, 254, 373 

L. myochrotim Nyl., 365 

L. scolimim Fr., 385 

L. tnrgidum Nyl., 385 

Leptorhaphis Koerb., 263, 316 

Lesdain, Bouly de, 140, 270, 271, 366, 369, 376, 

398 

Letharia A. Zahlbr., 84, 340 

L. viilpina Wain., 95, 105, 226, 228, 246, 265, 

349, 364, 410, 417 

Lett, 19 

Lettau, 225, 227, 369, 391, 417 

Lichen, xxvi, i, 5, 9, 303 

Lichen albineus Ludw. , 354 

Lichen candelarius L., 371, 415 

Lichen dneretis terrestris, 407 

Lichen dichotomus Engelh., 354 

Lichen diffusus Ludw., 354 

Lichen gelatinosus Rupp, 6 

Lichen juniperinus L.. 415 

Lichen orbiculatus Ludw., 354 

Lichen parietinus L., 371, 415 

Lichen Roccella L., 415 

Lichen saxatilis L., 415 

Lichen tartareus L., 415 

Lichen tenellus Scop., 371 

Lichenacei, 306 

Lichenes Coralloidei etc. Hall. , 7 

Lichenodium Nyl., 334 

Lichenoides, i, 6, 7, 304, 415 

Lichenophoma Keisz., 201 

Lichenoxanthine, 418 

Lichina Ag., 163, 195, 201, 233, 281, 284, 334, 

383 

L. confinis Ag., 383, 384 

L- pygfnaea Ag., 195, 201, 383 

INDEX 

Lichinaceae, 55, 99, 310, 333 

Ltchtnella Nyl., 354 

Lightfoot, 9, 280/303, 407, 415 

Limax, 396 

Lindau, 18, 34, 36, 48, 64, 67, 78, 108, 149, 164, 

168, 170, 176, 178, 184, 233, 269, 330 

Lindsay, xx, 16, 17, 19, 120, 193,203, 252, 262, 

266, 348, 354, 358, 391, 401, 415, 417 

Link, 371 

Linkola, 141 

Linnaeus, 7, 142, 154, 304, 312, 392, 401, 409, 

Lister, 267 

Listerellaparadoxa]2hn., 267 

Lithographa Nyl., 322 

Lithoicea Massal., see Verrucaria 

L. lecideoides Massal., 373 

Lithothelium Miill.-Arg., 317 

Litmus, 413 

Lobaria Schreb., 136, 182, 287, 336 

L. laciniata Wain., 133, 134 

L. laelevirens A. Zahlbr., 2, 196 

L. pulmonaria Hoffm., 2, 3, 10, 90, 96, 126 

(Fig. 127), 130, 195, 252, 267, 336, 400, 406, 

408, 411, 416, 418 

L. scrobiculata DC., 130, 143 

L'Obel, 2 

Lopadiopsis Wain., 327 

Lopadium Koerb., 191, 329 

Lophothelium Stirt., 319 

Loxa (Cinchona), 364 

Ludwig, 354 

Luffia lapidclla, 399 

Lung-wort, 406, 409 

Lutz, 1 08 

Luyken, xx, 156, 184 

Lycoperdaceae, 307 

Lyell, 14 

Lyngbya Ag., 136 

Mackay, 13 

McLean, 385 

Macmillan, 357, 391 

Maheu, 243, 387 

Maire, 185, 186, 189 

Malinowski, 74, 371, 374 

Malme, 261 

Malpighi, 5, 142, 155 

Manna, 404, 422 

Marchantia L., i, 5 

Maronea Massal., 331 

Martindale, 19 

Martius, 15 

Massalongia Koerb., 287, 335 

Massalongo, 16, 188, 305 

Massee, 308 

Mastoidea Hook, and Harv., 315 

Mastoidiaceae, 60, 309, 315 

Mattirolo, 152 

Maule, 162, 164 

Mayfield, 368 

Mazosia Massal., 59, 323 

Mead, Richard, 407 

Megalospora Mey. and Flot., 329 

Melampydium Miill.-Arg., 325 

Melanotheca Miill.-Arg., 317 

Melaspilea Nyl., 321, 322

Mereschkovsky, 258 

Merrett, 3 

Metzger, 176, 240 

Meyer, 13, 46, 51, 126, 143, I5 6, 187, 252, 258, 

35 

Micarea Fi:, see Biatorina Massal. 

Michael, 397 

Michaux, 14 

Micheli, i, 6, 142, 155 

Microcystis Kiitz., 52, 319 

Microglaena Lonnr., 314 

Micrographa Miill.-Arg., 322 

Microphiale A. Zalilbr., 328 

-Wicrotkelia Koerb. , 316 

Microtheliopsis Miill.-Arg., 318 

Minks, 26 

Minksia Miill.-Arg., 323 

Mites, 395, 397 

Miyoshi, 256, 403 

J\Iniu>H hornutn L. , 65 (Fig. 35) 

Moebius, 62 

Mohl, 185, 1 86 

Molisch, 250 

Moller, 49, 154, 196, 202, 203 

J\Ioia orion, 399 

Monas Lens, xx 

Monasats, Van Teigh. , 1 78 

Montagne, 15 

Moreau, xxi, 168, 175, 176, 212, 266 

Moriola Norm., 313 

Moriolaceae, 309, 313 

Morison, i, 4, 5, 155, 304 

Moss, 356 

Mousse des Chenes, 418 

Mudd, 16, 17, 19 

Muenster, 354 

Mtihlenberg, 14 

Mulder, 210 

Miiller(-Argau), 18, 26, 191, 192, 205, 278, 307, 

353' 4r 

M filler, K. 212 

; 

Miillerella Hepp, 275 

Mitsco-fnngns, \ 

Mnsens, i 

Must-its cranii huinani, 413 

Musk, 419 

Mycetozoon on Lichens, 267 

Ulycoblastus Norm., 329 

J/. sangitinarius Th. Fr., 188 ; see Lecidca 

Mycocalicium Rehm, 277 

M. parietinuin Rehm, 277 

Mycoconiocybe Rehm, 277 

Mycoidea Cunningh., 35, 59, 309, 318, 352, 363 

.}/. parasitica Cunningh., 36, 59 (Fig. 31), 

60 

Mycoideaceae, 59 

Mycoporaceae, 309, 318, 352 

Mycoporellum Zahlbr., 159, 3x8 

Mycoporum Flot., 159, 276, 318 

Mycosphatrella Johans., 39 

Mycosphaerellaceae, 275 

Myriangiacei, 306 

Myxodictyon Massal., 338 

Myxophyceae, xix, *i, 52-55, 60, 68, 272, 324, 

385 

Narcyria monilifera, 399 

INDEX 457 

Necker, 123, 154 

Nees von Esenbeck, xxiv 

Neophyllis Wils., 330, 351 

Nephroma Ach.,63, 135, 136, 169, 244,186, 337, 

348 

N. expallidum Nyl., 139 (Fig. 79) 

Nephromium Nyl., 63, 158, 175, 200, 122, 244, 

283, 286, 337, 349, 351 

N. laevigatutu Nyl., 195 

N. lusitanicum Nyl., 218, 246 

N. tomentosum Nyl., 87, 128, 169 

Nephromopsis Miill.-Arg., 158, 244, 339 

Neubert, 410 

Neubner, 62, 175, 189, 188 

Neuropogon Flot. and Nees, 346 

Nienburg, 38, 64, 123, 166, 167, 168, 169, 177, 

185, 196, 240 

Nilson, 147, 151, 250, 358, 389 

Norman, 16, 313 

Normandina Nyl., see Corisciutn 

Normandina Wain., 315 

Nostoc Vauch., 20, 21, 23, 24, 26, 27, 32, 41, 53, 

61, 63, 69, 136, 138, 232, 246, 266, 285, 

yxêtseq., 396 

N. coernlescens Lyngb., 53 (Fig. 18) 

N. lichenoides Kiitz., xx, 54 

N. Linckia Born., 53 (Fig. 18) 

ff. sphaericum Vauch., 54 

N. symbioticum, 45 

Nostocaceae, 25, 53 

Notaris, De, i, 15, 16 

Notaspis lutontm, 397 

Nyc tails Fr., 261 

Nylander, xxi, 7, 8, 16, 18, 25, 30, 52, 126, 131, 

'35. 136, 152, 197, 228, 262, 306, 325, 350, 

353, 3' 383 

Nylanderitlla Hue, 315 

Obryzum Wallr., 363 

Ocellularia Spreng., 326 

Ochrolechia Massal., 338 

O. pa'.lescens Koerb., 187 (Fig. 106), 213 

Ochrophaeae Wain., 295 

Officinal barks, 15 

Ohlert, 234 

Oidia, 189 

Olivier, 342 

Omphalaria Dur. and Mont., 348, 3/3, 393 

O. Heppii MUll., 63 

O. pulvinata Nyl., 373 

Oniscus, 396 

Oospora Wallr., 45 

Opegrapha Ach., n, 13, 35, 184, 304, 321, 321, 

353- 354. 36 ' 

O. atra Pers., 15, 202 

O. calcarea Turn., 383 

O. endoleuca Nyl., 243 

O. hapalea Ach., 243 

O. saxicola Ach., 216, 219 

O. subsiderella Nyl., 50, 202, 349 

O. Thomasiana Goepp., 354 

0. varia Pers., 354, 365 

O. vulgata Ach., 30 

O. zonata Koerb., 392 

Opegraphella Miill.-Arg., 322 

Orbilia coccinella Karst., 261 

Orchil lichen, 412, 416

458 

Oribata Parmeliae, 397 

Oribatidae, 397 

Oropogon Fr., 340 

O. loxensisTh. Fr., 130, 210, 352 

Orphniospora Koerb., 329 

Orthidium, 191 

Orthoptera, 397 

Oscillaria Bosc., 24 

INDEX 

Pachyphiale Lonnr., 328 

Padina Pavonia Gaillon, 153 

Palmella Lyngb., 24, 57, 232, 278, 282, 289, 309, 

3 2 *> 338, 353 

P. botryoides Kiitz., 313 

Pannaria Del., 61, 79, 81, 135, 168, 175, 336, 

39 2 

P. brunnea Massal.', 244, 370 

P. microphylla Massal., 81, 244 

P. pezizoides Leight., 63 

P. rtibiginosa Del., 283 

P. triptophylla Nyl., 244 

Pannariaceae, 54, 135, 285, 287, 311, 335 

Pannoparmelia Darbish., 338 

P. anzioides Darbish., 90 (Fig. 51) 

Paracelsus, 407 

Paratheliaceae, 309, 316, 352 

Parathelium Mull.-Arg., 317 

Parfitt, 95 

Parkinson, 3, 407 

Parmelei, 353 

Parmelia Ach., 84, 86, 93, 94, 95, 133, 200, 213, 

227, 231, 238, 241, 242, 249, 260, 264, 267, 

269, 299, 300, 305, 346, 347, 348, 349, 351, 

354. 364, 372, 4M 

P. acetabulum Dub., 30, 167, 169 (Fig. 90), 

170, 180, 195 (Fig. in), 231, 255, 259, 360 

P. adgluthiata Floerk., 365 

P. aleurites Ach., 364 

P. alpicola Fr., 18, 350, 387 

P. aspidota Rosend. (see P. exasperata), 92 (Fig. 

53). 17. 338 

P. Borreri Turn., 265 ; 

see P. dubia 

P. caperata Ach., 88 (Fig. 49), 253, 255, 365, 

366, 395 

P. cetrata Ach. , 92 

P. conspersa Ach., 194, 

376, 416, 417 

P. crinita Nyl., 365 

P. dubia Schaer., 377 

241, 242, 355, 369, 

P. encausta Ach., 268, 388, 393 

P. enteromorpha Ach., 131 

P. exasperata Carroll, 62, 129 (Fig. 74), 132, 

196 

P.farinacea Bitt., 131, 143 

P.fuligitwsa Nyl., 247, 361, 376, 386 

P.glabra Nyl., 87, 170, 176 

P. glabratula Lamy, 1 70 

P. glomellijera Nyl., 249, 251 

P. hyperopta Ach., 261 

P. isidiophora A. Zahlbr., 66 

P. Kamtschadalis Eschw. , 300 

P. lacunosa Meng. and Goepp., 355 

P. lanata Wallr., see P. pubescens 

P. locarensis Zopf., 249 

P. molliuscula Ach., 265 

P. Mougeotii Schaer., 375 

P. obscurata DC., 64, 131, 176, 242 

Parmelia olivacea Ach., 247, 365 

P. omphalodes Ach., 3, 260, 37=;, 387, 415 

(Fig. 135) 

P. papulosa Rosend., 150, 214, 219 

P. perforata Hook. (?), 365 

P.perlata Ach., 92, 114, 213, 237, 243, 262, 

353. 363. 403. 4i6 

P. pertusa Schaer. , 131 

P. physodes Ach., 64, 91, 144 (Fig. 83), 146 

(Fig. 84), 156, 194, 234, 237, 242, 253, 262, 

299> 355. 361, 363. 366, 384, 385, 416 

P. pilosella Hue, 92 

P. proboscidea Tayl., 92, 150 

P. prolixa Carroll, 241, 249, 382 

P. pubescens Wain., 85, 299, 300, 350, 375, 

387 

P. revoluta Floerk., 247, 259 (Fig. 121) 

P. saxatilis Ach., 169, 170, 242, 243, 253, 

260, 355, 361, 365, 366, 375, 386, 387, 393, 

407 (Fig. 131), 416 

P. scortea Ach., 150, 366 

P. stygia Ach., 130, 299, 350, 375, 387, 393 

P. subaurifera Nyl., 143, 226, 246, 377 

P. sulcata Tayl., 144, 361 

P. tiliacea Ach., 164, 170, 252, 365 

P. tristis Wallr., 88, 130, 247, 375, 387 

P. vemuulifera Nyl., 87, 143, 214 

P. vittata Nyl., 131, 143 

Partneliaceae 200, 287, 298, 311 

Parmeliales, 308 

Parmeliella Mull.-Arg., 81, 286, 336 

Parmeliopsis Nyl., 339 

Parmentaria Fee, 3 1 7 

Patellaria Fr., 280 

Patellariaceae 278 

Patinella Sacc., 279 

P. atryviridis Rerun, 278 

Patouillard, 389 

Paulia Fee, 284, 333, 352 

Paulson, 244, 254, 366 

Paulson and Hastings, 28, 38, 44, 56, 260 

Paulson and Thompson, 254, 361, 369, 377, 397 

Peccania Forss., 284, 333, 373 

Peirce, xxiii, 33, 34, 108, 258, 359 

Peltati, 305 

Peltidea Ach., 63, 286, see Peltigera 

Peltigera Willd., 3, 42, 53, 6r, 63, 88, 135, 136, 

137, 168, 175, 186, 204, 212, 213, 222, 232, 

242, 257, 266, 283, 286, 337, 346, 349, 355, 

367, 384, 385, 392 

P.americana Wain., 351 

P. aphlhosa Willd., 26, 87, 133, 138 (Fig. 

78 A, B), 141, 211, 262, 347, 359, 370, 406 

P. canina Willd., 24, 51, 84 (Fig. 47), 87, 89 

(Fig. 50), 93 (Figs. 54, 55), 97, 185, 213, 

254, 262, 359, 367, 370, 394, 396, 407, 418 

P. horizontalis Hoffm., 169, 244 

P. lepidophora (Nyl.) Bitt., 140 

P. leptoderma Nyl., 351 

P. malacea Fr., 169, 370 

P. polydactyla Hoffm., 51, 244, 266, 368 

P. ntfescens Hoffm., 169, 386 

P. spuria Leight., 268, 369 

P. spuriella Wain., 351 

P. venosa Hoffm., 244, 347 

Peltigeraceae, 54, 135, 283, 286, 287, 311, 336 

Pelvetia canaliculata Dec. and Thur., 39

Pentagenella Darbish., 83, 324 

Perforaria Mlill.-Arg., 337 

Persio, 413 

Persoon, 10, 21, 123, 156, 395 

Pertusaria DC., 34, 73, 85, 86, 88, 170, 180, 

186, 213, 246,253, 337, 4 [ 4 

P. amara Ach., 148, 236, 243, 349, 361, 366, 

408 (Fig. 132) 

P. comtnunis DC., 50, 202, 214 (Fig. 116), 

255, 269, 366, 393 

P. concreta Nyl., 382 

P. corallina (Ach.) Bachm., 374 

P. dactylina Nyl., 387 

P.dealbataC., 215, 375, 376 

P. faginea Leight., 396 

P. globulifera Nyl., 33 (Fig. 12), 236, 237, 262, 

357, 366 

P. glomerata Schaer., 387 

P. lactea Nyl., 374, 376 

P. leioplaca Schaer., 365 

P. hitescens Lamy, 226 

P. melaleuca Dub. ,417 

P. oculata Th. Fr., 387 

P. velata Nyl., 265 

P. Wulfenii DC., 226, 366 

Pertusariaceae, 147, 311 

Petch, 397 

Petiver, 4, 10 

Petractis Fr., 327 

P. exanthematica P'r., 61, 75, 215, 216 

Peziza Dill., 157, 213, 307 

/'. resinae Fr., 355 

Pfaff, 221 

Pfeffer, 220 

Phacopsis vulpina Tobl., 265 

Phaeographina Miill.-Arg., 322 

Phacographis Miill.-Arg., 322 

Ph. Lyellii A. Zahlbr., 350 

Phaeotrema Miill.-Arg., 326 

Phalena, 395 

Phascum cuspidatum Schreb., 45 

Phialopsis rubra Koerb., 174, 249; see Gyalecta 

Phillips, 252 

Phleopeccarua Stein., 284, 333, 352 

Phlyctella Miill.-Arg., 338 

Phlyctidia Miill.-Arg., 338 

Phlyetis Wallr., 338 

P. agelaea Koerb., 174 

Phycolichens, 22, 282, 283, 285 

Pliycopeltis Millard., 59, 278, 318, 321, 322, 323, 

3 2 7. 35 2 , 3 6 3 

P. expansa Jenn., 35 (Fig. 13), 60 (Fig. 32) 

Phyllactidium Moeb., 59, 62, 288, 309, 310, 318, 

327, 363 

P. tropiciim Moeb., 59 

Phylliscidinm Forss., 333 

Phylliscum Nyl., 286, 33} 

Phyllobathelium Miill.-Arg., 318 

Phyllophora Grev., 1 1 1 

Phyllophthalmaria A. Zahlbr., 326, 352 

Ph. coccinea A. Zahlbr., 352 

Phylloporina Miill.-Arg., 318 

Phyllopsora Mull.-Arg., 329 

P. furfuracea A. Zahlbr., 329 

Phyllopsoraceae, 310, 329 

Phyilopyreniaceae, 309, 318 

Phymaloidei, 304 

INDEX 459 

Physda Schreb., 90, 94, 166, 186, 238, 301, 351, 

37?. 399 

P. aipolia Nyl., 20 (Fig. i), 249 

P. aquila Nyl., 380, 382, 384 

P. ascendens Bitt., 270, 369, 377 

P. caesia Nyl., 226, 369, 384 

P. chrysophthalma, see Teloschistes 

P. ciliaris DC., 3, 46, 84 (Fig. 48), 92, 94, 99, 

103, 155, 165 (Fig. 94), 166, 167, 182 (Fig. 

too), 184, 185 (Fig. 104), 187, 189, 191, 

243, 246, 247, 355, 360, 411, 419 

P. granulifera Nyl., 365 

P. hispida Tuck., 29, 92, 146, 164, 166, 169, 

194 ( Fi g- IIO )> 2 4i, 271, 360, 366 

P. hypoleuca Tuck., 399 

P. intricata Schaer., 301 

P. Uncomelas Mich., 99 

P. obscura Nyl., 243, 360, 365, 369, 377 

P. parietina (see Xanthoria), 29 (Figs. 7, 8) 

P. picta Nyl., 349, 353 

P. puherulenta Nyl., 28, 164 (Fig. 93), 166, 

181, 248, 360, 365, 366, 377, 399 

P. punctieulata Hue, 33 

P. sciastrella Harm., 369 

P. stdlaris Nyl., 29, 365, 384 

P. slellaris var. teiulla Cromb. , see P. hispida 

Tuck. 

P. subobscura A. L. Sm., 384 

P. tenella Bitt., 366, 384, 386 

P. tribacia Nyl., 365 

P. villosa Dub., 268 

Physciaceae, 136, 200, 267, 300, 308, 311, 341 

Physcidia Tuck., 299, 339 

Ph. Wrightii Nyl., 352 

Physma Massal., 163, 284, 334, 341 

P. chalazanum Arn., 32 (Fig. 9) 

P. compaction Koerb., 163, 266 

P. franconicum Massal., 263 

Pilocarpaceae, 310, 325 

PMocarponVfain., 325, 353; see Pilophorus 

P. leiicoblepharum Wain., 325, 363 

Pilophorus Th. Fr., 17, 125, 133, 135, 201, 292, 

294, 297, 330 

P. robuslus Th. Fr., 136 

Pinus sylvestris L., 94, 271 

Piptocephalis De Bary, 261 

Placidiopsis Beltr., 288 

Placodium DC., 80, 339, 340, 346, 360, 372 

P. atroflawm A. L. Sm., 386 

P. aurantiacum Hepp, 365 

P. bicolor Tuck., 136 

P. callopismum Mer., 349 

P. cerinum Hepp, 262, 365, 366, 367 

P. ritrinum Hepp, 224, 271, 349, 373. 377. 

P'. dedpiens Leight., 218, 369, 383 

P. elegans DC., 225, 241, 34?- 39 39 

P.ferntgineum Hepp, 346, 384 

P.flavescens A. L. Sm., 377 

P. fruticulosum Darbish., 34? 

F. Gray, 367 

P.fulgensS. 

P. lacteum Lesil., 377 

P. lobulatum A. L. Sm., 379, 382, 34 

P. luteoalbum Hepp, 301 

P. murorum DC., 42, 80 (Fig. 42), / *4' 

243. 347, 369, 3o 

P. nivale Tuck., 301

460 

INDEX 

Placodium pyracewn Anzi, 369, 377 

P. rupestre Br. and Rostr., 301 

P. subfruticulosum Elenk., 347 

P. sympageum, see P.flavescens 

P. tegularis (Ehrh.) Darbish., 379, 384 

P. teicholytum DC., 369 

Placodium Hill (non DC.), 8 

Placodium Web. (non DC.), 9 

P. Garovagli (Koerb.) Fried., 8 1 

P. saxicolum S. F. Gray, 146, 168; see 

Lecanora 

Placolecania Zahlbr., 338 

Placothelium Miill.-Arg., 285, 319 

Placynthium Ach., 336 

P. nigrum S. F. Gray, 248, 373 

Plagiothecium sylvaticum Buch. and Schimp., 

237 

Plagiotrema Miill.-Arg., 317 

Platygrapha Nyl. , 325 

see Cetraria 

Platysma Nyl., 8, 200, 257; 

P. commixtum Nyl., 375 

P. corniculatum Hill, 8 

P. Fahlunense Nyl., 375 

P. glaucum Nyl., 10, 375, 376, 418 

P. lacunosa Nyl., 375 

Pleospora collematum Zuk., 163, 266 

Pleurococcus Menegh. (?), 22, 29, 62 

P. Naegeli Chod., 28 

P. vulgaris Menegh., 28, 55 (Fig. 22), 223 

P. vulgaris Naeg., 28 

Pleurocybe Mull.-Arg., 320 

P. madagascarea A. Zahlbr., 289 

Pleurothelium Miill.-Arg., 317 

Plenrotrema Miill.-Arg., 317 

Plot, 4 

Plowright, 207 

Plukenet, 5 

Poa eompressa L., 393 

Podtiridae, 256 

Polyblastia Massal., 48, 314 

P. catalepta (Ach.) Fuist., 30 

P. Vouauxi Lesd., 378 

Polyblastiopsis Nyl., 316 

Polycauliona Hue, 339, 340, 346 

P. regale Hue, 339, 346 

Polycaulionaceae, 339 

Polychidium A. Zahlbr., 284, 332 

Poly coccus Kiitz., 24 

P. punctiformis Kiitz., 24, 54, 61 

Polyporus Mich., 261 

Polysticlus versicolor (Fr.), 152 

Polystigma rubrum DC., 178, 207 

Polystroma Clem., 326 

P. Ferdinandezii Clem. , 326 

Polytrichum L., 392 

P. commune L. f 237 

Polyxenus, 270 

Porina Ach., 204, 316 

P. lectissima A. Zahlbr., 249, 251, 392 

P. olivacea A. L. Sm., 159 (Fig. 90 A) 

Porocyphus Koerb., 332 

PororuaVfiOA., 13, 178 

Porta, 5 

Porter, 109, 270 

Prasiola Ag., 60, 309, 315 

P.parietina Wille, 60 (Fig. 33) 

Prasiolaceae, 60 

1 1 

Propagula, 

Protocaliceaceae, 277 

Protococcaceae, 55, 288, 291, 309, 310, 313 et 

seq., 353 36 3 

Protococcus Ag., xx, 28, 56, 62, 63, 65, 287 

P. botryoides Kirchn., 65 

P. -viridis Ag., 22, 28, 44, 48 (Fig. 15), 55, 

(Fig. 22), 65, 313 

Pseudopyrenula Miill.-Arg., 316 

Psocus, 397 

Psora (Lecided) decipiens Hook., 388 

Psorella Miill.-Arg., 329 

Psoroglaena Miill.-Arg., 315 

Psoroma S. F. Gray, 136, 285, 286, 335 

P. hypnorum S. F. Gray, 63, 8i, 88, 89, 135, 

246, 283, 370 

Psoromaria Nyl., 285, 286, 335 

Psorotichia Massal., 68, 163, 333, 373 

Ps. higubris Dal. Tor. and Sarnth., 375 

Ps. lutophila Arn., 368 

Psychides, 399 

Pterygiopsis Wain., 332 

Pterygium Nyl., 333 

Pt. Kenmorensis A. L. Sm., 392 

Ptychographa Nyl., 321, 322 

Pulteney, 4, 14 

Pulvis antilyssus, 407 

Pulvis Cyprius, 419 

Pycnothelia ( Cladonia] papillaria Duf., 369 

Pyrenastrum Eschw., 317 

Pyrenidiaceae, 53, 54, 275, 285, 309, 319 

Pyrenidium Nyl., 285, 319 

P. actinellum Nyl., 99 

Pyrenocarpeae, 158, 273, 308 

Pyrenocarpei, 306, 307, 353 

Pyrenocarpineae, 273, 275, 288, 308 

Pyrenocollema Reinke, 334 

Pyrenographa Miill.-Arg., 323 

Pyrenolichens 159, 241, 276, 352, 391 

Pyrenomycetes 158, 267, 273 

Pyrenopsidaceae, 282, 284, 310, 352 

Pyrenopsidium Forss., 333 

Pyrenopsis Nyl., 60, 68, 163, 175, 333 

P. haematopis Th. Fr., 195 

P. impolita Forss., 175 

P. phaeococca Tuck., 175 

Pyrenothamnia Tuck., 99, 315 

P. Spraguei Tuck., 288 

Pyrenothamniaceae, 309, 315 

renothea Ach., 192 

thrix Riddle, 319 

enula Ach., 200, 316 

P. tinerella Fink, 365 

P. leucoplaca Koerb., 365 

P. nitida Ach., 174, 194, 240, 255, 350, 354, 

3 6 4, 365 

P. thelena Fink, 365 

Pyrenulaceae, 50, 276, 309, 316, 365 

Pyrgidium Nyl., 319 

P. bengalense Nyl., 353 

Pyrgillus Nyl., 289, 320 

Pyronema Carus., 167 

P. confluens1v\., 178 

Pyxidium Hill, 8 

Pyxine Nyl., 301, 341 

P. Cocoes Nyl., 353 

P. Meissnerii Tuck., 353

Quercus alba, 359 

Q. chrysolepis, 359 

Q. Douglasii, 359 

Racodium Pers., 35, 328 

K. rupestre Pers., 291, 328 

Radais, 42 

Ramalina Ach., 3, 84, 103, no, 195, 213, 238, 

244, 257, 270, 305, 340, 347, 348, 351, 359, 

361, 363 

R.calicaris Fr., 3, 104, 147, 210, 353, 355, 

365, 366, 418, 419 

A', ceruchis De Not., 103 

R. Curnowii Cromb., 104, 109 

A*. cuspidataN'y\,\ 225, 271 (seeR.siliquosa),^^ 

R. dilacerata Hoffm., 106, 130 

R. Eckloni Mont., 130 

R. evernioides Nyl., 103, 300 

A'.farinaceaAch., 10,239, 2 ^9> 271,353, 3^6, 

400, 411 

R.fastigiata Ach., 109, 365, 366, 400, 411 

R.fraxinea Ach., 104, 106, 130 (Fig. 75 A), 

155, 164, 170, 195, 200, 212, 215, 300, 355, 

365, 366, 400, 411. 418 

A', gracilenta Ach., 349 

R. homalea Ach., 103 

A'. Landroensis Zopf, 109, 130 

A 1 

, mimtscula Nyl., 103 (Fig. 62), 147 

R. pollinaria Ach., 109, 227, 349, 366 

R. reticulata Krempelh., 33 (Fig. u), 99, 106 

(Fig. 64), 253, 257, 359 

A', scopulorum Ach., see R. siliquosa 

R. siliqitosa A. L. Sm. , 104, 109 (Fig. 65), 

130, 224, 225, 271, 300, 379 (Fig. 122), 381 

(Figs. 123, 124) 

A', strepsilis Zahlbr., 104, 130 (Fig. 75 B) 

R. subfarinacea Nyl., 380 

R. tertiaria Engelh., 354 

Ramalinaceae, 339 

Ramalinites lacerns Braun, 354 

Ramalodei, 306 

Romania Stizenb. , 328 

Rathapu, 403 

Ray, 4 , 407, 409 

Rees, 27 

Rehm, 277 

Reindeer, 401 

Reindeer moss, 400 et passim 

Reinke, 18, 31, 41, 68, 123, 125, 130, 144, 253, 

277, 284, 291, 307, 324 

Reinkella Uarbish., 83, 324 

Relhan, 9 

Rhabdopsora Mtill.-Arg., 319 

Rhizina unditlata Fr. , 181 

Rhizocarpon Ramond, 248, 302, 329, 341 

A", alboatrum Th. Fr., 365, 369, 373, 383 

A', concentricum, see R. petraettm 

R. confervoides DC., 71 (Fig. 38 A, B), 369, 386 

R. distinctnm Th. Fr., 261 

R. epipolium (Ach.), 265 

R. geographicum DC., 73, 74 (Figs. 40, 41), 

226, 236, 243, 246, 249, 252, 261, 264, 291, 

346, 372, 374, 37 6 - 38o 

A", obscuratum Massal., 392 

A'. Oederi Koerb., 375 

A', petraenm Koerb. (?), 374 

Jf.petraeumM&ssai., 171 (Fig. 97), 375, 392 

INDEX 461 

Rhizocarpon viridiatrum Koerb., 249, 37*, 

3/6 

Rhizomorpha Roth, 12 

Rhymbocarpus pututiformis Zopf, 164 

Ricasolia De Not., 94 (see Lobaria), 168, 175 

R. amplissima De Not., 133, 134 (Fig. 76), 

'95, 197- 357 

R. lattevirens Leigh t., 357 

Richard, 377, 411 

Richardson, Dr, 6 

Richardson, Sir John, 388 

Riddle, 137 

Rinodina S. F. Gray, 301, 302, 341, 371 

A', archaea Wain., 346 

A'. Conradi Koerb., 370 

R. f i a s - F. ? S? Gray, 366, 367, 377, . 

383. 384 

A', isidioides Oliv., 301 

R. oreina Wain., 301, 374, 390 

R. sophodes Th. Fr., 367 

A', turfacea Th. Fr., 262, 377 

Rivularia, 55, 136, 138, 284, 333 

A'. Biasolettiana, 54 (Fig. 21) 

A', minutula Born, and Fl., 54 (Fig. 21) 

R. nitida Ag. , 55 

Rivulariaceae, 54 

Roccella DC., 3, 34, 35, 83, 103, 200, 125, 233, 

242, 278, 292. 324, 351, 359, 363 

R.fudformis DC., 83 (Fig. 45), 98 (Fig. 57), 

101, no, 227, 228, 349, 350, 412 

R.fucoidfs Wain., 349, 350 

A'. Alontagnei Bel., 213, 413 

R. , peritensis Kremp. 413 

A', phycopsis Ach., 1 10 ; see R. futaides R. portentosa Mont., 413 

R. sinnensis Nyl., 413 

R. tinctoria DC., 213, 215, 227, 349, 350, 413 

(Fig- '33) 

Roccellaceae, 59, 83, no, 279, 290, 309, 333 

Roccellaria Darbish., 323, 324 

Roccellina Darbish., 83, 290, 323, 324 

Roccellographa Stein., '83, 290', 323, 324 

Rock tripe, 404 

Roebuck, 401 

Ronceray, 213, 413 

Rosendahl, 86, 90, 93, 129, 170, 176, 214, 218, 

249 

Roses, spirit of, 419 

Roy, 41 1 

Ruel, 2 

Rupp, 5 

Russula Pers., 161 

Sachs, 17, 23 

Sagedia, see Verntcaria 

S. declivum Arn., 251 

Sagiolechia Massal., 328 

Salix repens L., 357 

Salter, 51, 393 

Sandstede, 233, 384, 385 

Sappin-Troufty, 207 

Sarcographa Fee, 323 

Sarcographina Miill.-Arg., 323 

latericola Stein., 76 

Sarcogyne ( = Biatorella) 

Sarcopyrenia Nyl., 314 

Saltier, 113, 173, 296, 358 

Schade, 376 

Schaerer, 15, 192

462 INDEX 

Schellenberg, in. 

Schenk, 213 

Schikorra, 178 

Schimper, 354, 355 

Schismatomma Flot., 325 

Schizopelte Th. Fr., 83, 324 

Schneider, 7, 135, 136, 139 

Schreber, 126 

Schrenk, 231, 258, 359 

Schulte, 1 104, 105, 06, 177 

Schvvarz, 224 

Schweinfurth, 405 

Schvveinitz, 15 

Schwenckfeld, 3 

Schwendener, xx, 2, 16, 17, 18, 25, 27, 36, 71,82, 

86, 92, 126, 128, 129, 142, 147, 168, 213, 

224, 307 

Sderophyton Eschw., 323 

S. circumscriptum A. Zahlbr., 322 

Scopoli, 8, 21, 154, 409 

Scott-Elliot, 253 

Scutellati, 305 

Scutovertes maculatus, 397 

Scytonema Ag., 54, 57, 61, 68, 75, 136, 153,216, 

232, 281, 284, yyjetseq., 318 

S. mirabile Thur., 53 (Fig. 19) 

Scytonemaceae, 54 

Secoliga (Gyalecta) bryophaga Koerb., 368 

Segestria, 

see Porina 

Senft, 223 

Septoria Fr., 204 

Sernander, 94, 140, 355 

Servettaz, 45 

Servit, 374 

Sherard, 4, 6, 7 

Sibbald, 409 

Sibtborp, 9 

Sievers, 230 

Simonyella Steiner, 324 

Siphula Fr., 340 

Strosiphon pulvinatus Breb. , 54 

Sloane, 10 

Smith, Lorrain, 328 

Smith, Sir J. E., 10 

Solorina Ach., 56, 63, 85, 94, 135, 136, 168, 175, 

176, 183, 287, 337," 39 2 

S. bispora Nyl., 135 

S. crocea Ach., 63, 88, 140, 210, 228, 246, 287, 

346, 388 

S. octospora Am., 85 

S. saccata Ach., 155, 244, 388 

S. spongiosa Carroll, 135, 186, 368 

Solorinetta Anzi, 337 

Sorby, 418 

Sowerby, James, 10 

Speerschneider, 17, 25 

Sphaeria Hall., 192, 213 

Sphaeriaceae, 307 

Sphaerocephalum Web., 9 

Sphaerophoraceae, 135, 309, 320 

Sphaerophoropsis Wain., 291, 329 

S. stereocauloides Wain., 292 

Sphaerophorus Pers., 83, 105, 184, 277, 289, 320, 

3 6l 375, 387, 393 

S. foralloides Pers., 83 (Fig. 44) (see S. globo- 

). 355, 375, 387, 388, 389 

S.fragihs Pers., 375, 387 

Sphaerophorus globosus A. L. Sm. , 346 

S. stereocauloides Nyl., 135 

Sphagnum Dill., 231, 355 

Spheconisca Norm., 313 

Sphinctrina Fr., 277, 319, 353 

Sphyriditim byssoides, 177 

S.fungiforme Koerb., 177 

Spilonema Born., 68, 333 

Spirographa A. Zahlbr., 322 

Spirogyra Link, 188 

Splachnum L., 5 

Sporocladus lichenicola Corda, 200 

Sporodinia Link, 188 

Sporopodium Mont., 327, 352 

S. Caucasium Elenk. and Woron., 353 

Sprengel, 21, 142, 156, 184 

Squamuria DC., 200, 298 

S. saxicola, see Lecanora 

Stahel, 220 

Stahl, 28, 30, 62, 160, 163, 173, 266, 395 

Stahlecker, 76, 235, 371, 374 

Staurothele'KoTm., 31, 62, 76, 314 

S. clopima Th. Fr., 391 

S. dopismoides Anzi, 249 

S, hymenogonia A. Zahlbr., 361 

S. umbrinum A. L. Sm., 373, 393 

Steganosporium cellulosum Corda, 201 

Steiner, 75, 179, 190, 198, 215, 276, 312, 353, 

389 

Steinera A. Zahlbr., 333 

Stenberg, 411 

Stenhouse and Groves, 228 

Stenocybe Nyl., 177, 319 

Stereocaulon Schreb., 17, 23, 83, 105, 125, 133, 

135, '76, 201, 283, 292, 294, 297, 330, 346, 

358, 361, 387 

S. alpmum Laur., 137, 346, 387 

S. condensation Hoffm., 319, 388 

S. coralloides Fr., 125, 375 

S. Delisei Borg., 375 

S. denudatum Floerk., 137, 375, 387 

S. evohitum Graewe, 375 

S. paschale Fr., 211, 372, 385, 391, 401 

S. ramulosum Ach., 125, 136 

S. salazinum Borg., 227 

S. tomentosum Fr. , 125, 136, 387 

Stereochlamys Miill.-Arg., 316 

Stichococcus Naeg., 62 

S. bacillaris Naeg., 42 

Sticta Schreb., 13, 63, 85, 86, 94, 136, 138, 200, 

283, 287, 336, 350, 351, 364, 392 

St. aurata Ach., 126, 128, 223, 226, 246, 350 

St. crocata Ach., 128, 246 

St. damaecornis Nyl., 127 (Fig. 73), 128, 210, 

35 

St. Dufourei Del., 128 

St. fuliginosa Ach., 126, 128, 223 

St. intricata Del., 128 

St. limbata Ach., 128 

St. oregana Tuck., 136, 139 

St. sylvalica Ach., 1 28 

Stictaceae, 96, 136, 286,311, 336, 347, 350, 418 

Stictidaceae, 278 

Stictina Nyl., 63, 168, 175, 287 

Stictis Pers., 278 

Stigmatea Fr., 275

Stigonema Ag., 23, 16, 54 (Fig. 20), 68, 136, 283, 

284, 310 et seq., 317 

.S. panniforme Kirchn. , 54 

Stigonemaceae, 54 

Stirton, 331, 350 

Stizenberger, 18, 128 

Stone, 399 

StreptothriA Cohn, 45 

Strigula Fr., 60, 65, 288, 318, 353, 363 

S. Bitxi Chod., 363 

S, complanata Mont., 35, 42, 59, 205, 260, 269 

5. t'legans Miill.-Arg., 205 

Strigulaceae, 59, 60, 204, 309, 318, 363 

Stiide, 2ii 

Sturgis, 97, 168, 175, 197, 289 

Snaeda fniticosa Forsk., 387 

Swartz, 10, 152 

Swedish moss, 415 

Symbiosis 3 1 

Synalissa Fr., 32, 33, 61, 284, 333, 373 

S. symphorea Nyl., 33 (Fig. 10) 

Synarthonia Miill.-Arg., 321 

Tabernaemontanus, 2 

Tapellaria Miill.-Arg., 327 

Taylor, 13, 149 

Tegeocrantis labyrinthicus, 328 

Teloschistaceae, 311, 341 

Teloschistes Norm., 85. 301, 341 

T. chrysophthalimis, Th. Fr., 92, 365, 367 

T. flaviians Norm., 3, 301, 341, 417 

Teras literana, 399 

7'ermes mcnoceros, 397 

Termites, 397 

Tetrany chits lapidus, 398 (Fig. 126) 

Tetrasporaceae, 57 

Thamnolia Ach. , 83, 101 (see Cerania), 246, 340, 

389 

Th. vermicularis Schaer., 346, 377 

Thamnonia Tuck., 339 

Thaxter, 178 

Thelenidia Nyl., 314 

Thelephora Ehrh., 281, 342 

Thelephoraceae, 152, 273 

Thdidea Hue, 335 

Th. forrugata Hue, 335 

Thelidium Massal., 314 

Th. microcarpiim A. L. Sm., 361 

Th. miniitiihtm Koerb., 253, 367 

Thelocarpon Nyl., 331 

Th. prasinelium Nyl., 367 

Th. turficoium Arn., 370 

Thclopsis Nyl., 316 

Thelotrema Ach., 3-26, 343 

Th. lepadinnm Ach., 397 

Thelotremaceae, 59, 302, 310, 326, 351, 352 

Thelotremei, 353 

Theophrastus, i, 2, 411 

Thernnitis Fr., 68, 284, 332 

Tholnrna Norm., 320 

Th. dissimilis Norm., 289 

Thomas, N., 59 

Thrambium Wallr., 192, 314 

T. epigaetim Wallr., 254, 367, 368 

Thwaites, 1 7 

Thyrea Massal., 284, 333 

Thysanothedum Berk, and Mont., 330 

INDEX 463 

Thysanothecium Hookeri Berk, and Mont., 294 

Ticothecium Flot., 275, 319 

T. pygmaeum Koerb., 267 

Tieghem, Van, 179 

Tobler, 43, 50, 148, 224, 253, 263, 265, 280 

Tomasiella Miill.-Arg., 317 

Toni, De, 60 

Toninia Th. Fr. , 329 

Torrey, 14 

Tournefort, i, 5, 155, 304 

Tournesol, 413 

Treboux, 40, 42 

Trematosphaeropsis Klenk., 266 

Tremotylium Nyl., 326 

Trentepohlia Born., 26, 30, 34, 59, 75, 78, 131, 

246, 276, 278, 287, 289, 291, 309, 316 etc., 

343. 35 2 3 6 5 

T. abietina Hansg., 65, 66 

T. aurea Mart., 34, 35, 58 (Fig. 29 A), 59 

T. jolt thus, 223 

T. umbrina Born. ,2 2, 34, 58 (Fig. 298), 59, 62, 

216 

Trentepohliaceae, 59, 288, 289 

Treub, 28, 394 

Treveris, Peter, 2 

Tricothelium Miill.-Arg., 318 

Trimmatothele Norm . , 314 

Tripe de Roche, 404 

Trypetheliaceae, 309, 317 

Trypethelium Spreng., 276, 317, 351, 364 

Jûbercularia Web., 9 

Tuckerman, 15, 136, 339 

Tulasne, 17, 25, 46, 70, 123, 159, 187, 189, 192, 

193, 200, 204, 263 

Turner, Dawson, 14 

Tutt, 399 

Tylophorella Wain., 320 

Tylophoron Nyl., 289, 320 

Uhlir, 43 

U lander, 21 1 

Uloth, 233 

Utnbilicaria., 17, 82, 200, 241, 262, 268, 331 

U. pushdata Hoffm., 86, 96, 150, 

240, 257, 414 

Unguentum Armarium, 407 

Unguentum sympatheticum, 407 

Urceolaria Ach., 48 ; see Diploschistes 

Urococats Kiitz., 57, 133, 318 

195, 214, 

Usnea Dill., i, 3, 7, 9, 83, in, 195, 213, 233, 

257, 268, 269, 300, 304, 305, 340, 347, 348, 

351, 361, 408, 419 

U. articulala Hoffm., 210, 268 

U. barbata Web., 25, 99 (Fig. 58), 104 (Fig. 

63 A), 130, 143 (Fig. 82), 167 (Fig. 95), 

168, 177, 200, 211, 215, 226, 234, 239, 246. 

339- 348,364, 4' 7 

U. ceratina Ach., 227 

U. compress a Hill, 8 

U. dasypoga Stiz., 359 

U. flonda Web., 91 (Fig. 52), 92, 210, 213, 

348, 363, 4" 

U. hirta Hoffm., 348, 355, 366 

U. laevis Nyl., 177 

U. longissima Ach., 85, 99, 102 (Fig. 61), 105 

(Fig. 638), 106, 215,348 

U. tnacrocarpa Arn., 177

464 

Usnea melaxantha Ach., 346 

U. plicata Web. , 359 

U. Taylori Hook., 104 

Usneaceae, 299, 311, 339 

Vaillant, 6 

Vallot, 253 

Valsa Fr., 317 

Varicellaria Nyl., 337 

V. microsticta Nyl., 77, 92, 187 (Fig. 126) 

Variolaria Ach. (see Pertusaria), 64, 171, 237 

Vaucheria sessilis DC., 65 (Fig. 34) 

Ventenat, 21 

Verrucaria Web. (non Pers.), 9, 174, 200, 275, 

3 1 4' 36 4 

V. aethiobola Wahlenb., 391, 392 

V. anceps Koerb., 377 

V. aquatilis Mudd, 383 

V. cakiseda DC., 176, 215, 219, 241, 373, 

398 

V. Dufourii'DC., 173 

V.fnscella Ach., 373 

V. f. Hoffmanni Hepp ; purpurascens Arn., 

251 

V. hydrela Ach., 391, 392 

V. lecideoides Koerb., 373 

V. mactiliformis Krempelh., 379 

V. margacea Wahlenb., 391, 392 

V. maura Wahlenb., 245, 383, 384, 386 

V. memnonia Flot., 383 

V. microspora Nyl., 256, 383, 386 

V. umcosa Wahlenb., 73, 383 

V. mnralis Ach., 30, 46 (Fig. 14), 70, 243, 

255. 361, 393 

V. nigrescent Pers., 56, 254, 369, 377, 392 

V. papillosa Ach., 377 

V. promimda Nyl., 383 

V. rupestris Schrad., 215, 243, 361 

V. scotina Wedd. , 383 

V. striatula Wahlenb., 383 

V. viridula Ach.', 391 

Verrucariaceae, 749, 309, 314, 353, 367 

Verrucarites geanthricis Goepp., 354 

Verrucula Stein., 265, 276 

V. aegyptica Stein., 276 

V. cahirensis Stein., 276 

Visiani, 405 

Volkard, 228, 410 

Vouaux, 267 

Wahlberg, n, 168 

Wahrlich, 51 

Wainio, 31, 48, 70, 112, 114, 118, 120, 122, 123, 

124, 125, 126, 128, 144, 153, 159, 163, 166, 

175, 177, 179, 188, 191, 240,276, 277, 292, 

294, 308, 344, 346, 348, 411 

Waite, 270 

INDEX 

Wallroth, xx, 13, 21, 22, 123, 133, 142, 156, 

192, 35 

Ward, Marshall, 35, 42, S9 

Watson, Sir W., 8 

Watson, 365, 373, 385 

Watt, 403 

Weber, i, 9 

Weddell, 252, 379 

Wehmer, 220 

Weir, 239 

West, G. F., 52, 54, 55, 56 

West, W., 225, 233, 357, 374 

Wester, 211 

Westring, 412 

Wettstein, 45 

Wheldon, 398 

Wheldon and Wilson, 360, 370, 373, 374, 379, 

384. 385. 3 8 7. 39i> 392 

Wiesner, 211, 241, 244 

Wilde, 395 

Wille, 28 

Willemet, 10, 401, 415 

Wilson, 350 

Winter, 30, 138, 263 

Winterstein, 209 

Wisselingh, 211 

Withering, 9 

Wolff, 124, 163, 170, 172, 176 

Woodward, 152 

Woronin, 28 

Woronina Cornu, 261 

Xanthocapsa (Sect, of gloeocapsa}, 52, 63, 284, 

33 2 i 373 

Xanthoria Th. Fr., 166, 246 

X. lychnea Th. Fr., 233, 252, 365, 417 

X. parietina Th. Fr., 3, 22, 24, 27, 28, 38, 42, 

48 (Fig. 15), 50, 56, 65, 67 (Fig. 36), 86, 

164, 176, 189, 195, 200, 224, 225, 227, 231, 

232, 2 4 I, 242, 253, 269, 270, 301, 341, 348, 

351, 360, 369, 373, 376, 380, 383, 384, 386, 

397, 406, 416, 418 

X. polycarpa Oliv., 365, 390 

Xylaria Hill, 12, 421 

Xylographa Fr., 278, 322 

X. spilomatica Th. Fr., 145 

Xyloschistes Wain., 322 

Zahlbruckner, A., 19, 59, 60, 66, 69, 275, 284, 

38, 335. 413 

Zopf, 19, 43, 108, 151, 188, 213, 221, 233, 238, 

246, 264, 265, 266, 268, 270, 395, 396, 398, 

4oo, 412, 417 

Zukal, 18, 26, 38, 6r, 68, 70, 82, 128, 129, 130, 

163, 179, 187, 215, 219, 230, 237, 244, 267, 

268, 271, 313, 395 

Zwelser, 419 

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