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Oomycetes Black & White Stock Photos
RMRDJ5CR–. Microbes, ferments and moulds . Bacteria; Fungi; Fermentation. 28 MICROBES, FERMENTS, AND MOULDS. cells is larger than the other, and persists alone up to the moment when the oospore is mature. It must, therefore, be regarded, as the female cell; while the. Fig, 15.—Reproductive organs of Mucor mucedo (much magnified). other, which is smaller and soon withers away, is the male cell. The mycelium of the oomycetes is developed in a more or less liquid medium, like all other decomposing and putrefying substances. The ordinary spores are. Please note that these images are extracted from scanned
RMRE3CRX–. A handbook of cryptogamic botany. Cryptogams. OOMYCETES 33» Schenk) ; or different individuals produce the oogones and the antherids (Lagenidium, Ancylistes). A perforation having been made in the oogonial wall, the whole of the protoplasm of the antherid empties itself into the oogone (there being no periplasm), and the united mass rounds itself off and becomes the oosperm. The germination of the oosperm has not been observed. Propagation takes place by means of zoospores (Lagenidium), and to this end either the whole thallus-hypha becomes transformed into a. zoosporange, or it is divided i
RMRDYG2W–. A textbook of botany for colleges and universities ... Botany. THALLOPHYTES 67 of zoospores, a feature which distinguishes the genus from Peronospora, under which the grape mildew was placed formerly. In the life history of Plasmo- para, therefore, zoospores, characteristic of Oomycetes, have been eliminated. This disease is of American origin and was unknown in Europe until American grape stocks were introduced as a protection against the destructive phylloxera. Peronospora. — These forms are very common parasites on ordinary vegetables, as peiis, beans, spinach, etc., and differ from Plasm
RMRE2MY9–. Elementary botany. Botany. 214 MORPHOLOGY. these views, might be presented here to show the general relationships of the fungi studied, with the addition of a few more in orders not represented above. It should be borne in mind that the author in presenting this view of classification does not necessarily commit himself to it. It is based on that presented in Engler & Prantl's Ptlanzenfamilien. There are three classes. I. Class Phycomycetes (Alga-like Fungi). 1. SUBCLASS OOMYCETES. 432. These arc the egg-spore fungi. They include the water mold (Saprolegnia), the downv mildew of the grap
RMRE3CRP–. A handbook of cryptogamic botany. Cryptogams. OOMYCETES 333' emerge again outside the oogonial wall, but they remain closed at all points, and after a day or two perish. In the case of certain species, the- antherids never produce these pro- cesses, or the oogones may be without antherids. In other cases antherids are never produced fit all, or only by way of rare exception. In the meantime the oospheres ripen into oosperms, while the antherids, if present, perish. Pringsheim has recently endeavoured to show that impregnation takes place in certain species by the transference into the oosphe
RMRDWPNH–. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. PHYTOPHTHORA 233 the ground, they can, in the presence of moisture, produce zoo- spores, as in Cysiopns. The first signs of disease are discoloured spots exhibiting a dark central region surrounded by successive zones of greyish and pale green tissue, which rapidly become brown or even blackish ; closer inspection discloses the white. Fig. 124.—Asexual reproduction in various Oomycetes. A, Small part of epidermis of Potato-leaf, infected with Blight (Phytophthora infes- ians), showing branched hypha; bearing
RMRDXNTG–. Botany of the living plant. Botany. PHYCOMYCETES.—(a) OOMYCETES 417 in America assumed epidemic virulence in Ireland, causing the great famine. Since that time the Potato crop has never been entirely free from it. The disease makes its appearance upon the leaves and stems as spots at first small and pale-coloured, but as they enlarge the centre of each becomes brown, and extends, though still with a pale margin, till the spots run together, and the whole leaf or even the whole shoot may be affected (Fig. 352). If leaves with young infected patches be examined on a damp still day, or better,
RMRDXNRT–. Botany of the living plant. Botany. PMYCOMYCETES.—(a) OOMYCETES z|2i moving freely in water, offers an interesting parallel with the pollen- tube in Seed-Plants. In both cases the male gamete is conveyed to the female by a method suitable for land-living plants. Comparison shows that both are modifications of organs originally developed to secure fertilisation through the medium of external water. The question will naturally arise whether any fungal type still shows a motile male gamete. This is found in Moiwblepharis, a fungus that lives saprophytically in water (Fig. 35S). Here a terminal
RMRDXNT6–. Botany of the living plant. Botany. PHYCOMYCETES.—(a) OOMYCETES 419 like those of Pythium, they are motile for a time by means of two cilia (Fig. 355). Coming then to rest, the cilia are dropped : each zoospore rounds itself off, and, investing itself with a wall, puts out a hyphal tube. If this takes place on the surface of a potato leaf, as it well might do under conditions of rain or heavy dew, all is ready for the infection. This may either be by entry through the pore of a stoma or by direct perforation through the epidermal wall (Fig. 356). By either route the parasite may reach the in
RMRE3CW0–. A handbook of cryptogamic botany. Cryptogams. OOMYCETES 323 ReessâUeber d. Entstehung d. Flechte Collema glaucescens (Monber. Berl. Acad., 1871). ReessâUeber d. Natur d. Flechten (Samml. wiss. Vortrage von Virchow u. v. HoltzendorfiF, 1879). SchwendenerâDie Algentypen d. FlecHengonidien (Basel, 1869). SchwendenerâErorterungen z. Gonidienfrage (Flora, 1872). SchwendenerâDie Flechten als Parasiten d. Algen (Verh. d. Basel, naturf. Ges., 1873). StahlâBeitr. z. Entwickel. d. Flechten, ii. (Leipzig, 1877). TreubâLichenencultur (Bot. Zeit., 1873). TreubâOnderzoek. over d. Natuur d. Lichenen (Diss.
RMRDXNW1–. Botany of the living plant. Botany. PHYCOMYCETES.- OOMYCETES 415 ends ol the hyphae, by their swelHng to an oval form, their storage with fine-grained protoplasm, and being shut off by a septum. The. Fig. 350. Portion of tissue near d in Fig. 348, higUy magnitied. The liyphae are seen running in all directions : at a, one passes through a stoma ; at c, a sporangium is about to form. (After Marshall Ward.) sporangium is readily detached, and germinates directly if the circum- stances are favourable. It then grows out into a fresh hypha, which may directly infect a new victim. If one is not wi
RMRDXT8E–. A manual of poisonous plants, chiefly of eastern North America, with brief notes on economic and medicinal plants, and numerous illustrations. Poisonous plants. EUTHALLEPHYTA—EUMYCETES—OOMYCETES 207. aiut.1* Fig. 51. At the left, leaf of Green Foxtail (Setaria zdridis), containing the oospores of Schrospora graminicola, a single spore at o. After Trelease. At the right, spike affected by the same fungus; b spikelet enlarged. The figure at the right, oospores from Hungarian grass; oog—Oogonium, oos—oosphere; oo—Oospore. The middle figure, Halsted; the right hand, Charlotte M. King.. Please no
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