Abstract
In the literature there is disagreement about the existence of a coleorhiza in cycad embryos. In this paper the terminology of the cycad ovule, seed and embryo is revised. It was confirmed that the cycad ovule and seed are pachychalazal and that the seed coat is exclusively formed by the pachychalaza. The term ‘pleurotesta’ as a substitute for the so-called ‘endotesta’ is suggested to describe the inner, membranous part of the seed coat. The anatomy of the cycad embryo was studied in comparison with the grass embryo and it was found that a coleorhiza does exist in cycad embryos and derives from the distal part of the suspensor. It is postulated that the coleorhiza in grasses also derives from the distal part of the suspensor and that the two structures are therefore structurally homologous.
Zusammenfassung
In der Literatur gibt es Unstimmigkeit über die Existenz einer Coleorhiza in Palmfarn-Embryonen. In diesem Dokument werden die Termen der Palmfarne Samenanlage, Saatgut und Embryo überarbeitet. Es wurde bestätigt, dass die Palmfarnen-Samenanlage und Saatgut Pachychalazal sind, und dass das Saatgut-Fell ausschließlich durch das Pachychalaza gebildet wird. Der Begriff * Pleurotesta * wird also als Ersatz für die so-genannten * Endotesta * vorgeschlagen, den inneren, Membranöse Teil des Saatgut-Fells zu beschreiben. Die Anatomie der Palmfarn-Embryos wurde untersucht, im Vergleich zu Gras Embryonen und es wurde gefunden, dass eine Coleorhiza in Palmfarn-Embryonen vorhanden ist und stammt von dem distalen Teil des Suspensors. Es wird postuliert, dass die Coleorhiza in Gräser auch abgeleitet ist aus dem distalen Teil des Suspensors und das beide Strukturen daher struktur-gemäss homolog sein.
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Robbertse, H.P.J., Grobbelaar, N. & du Toit, E. Origin of the Coleorhiza in Cycad Seedlings and its Structural Homology with That of the Poaceae. Bot. Rev. 77, 1–10 (2011). https://doi.org/10.1007/s12229-010-9058-4
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DOI: https://doi.org/10.1007/s12229-010-9058-4