. A manual of botany. Botany. MORPHOLOGY OF REPRODUCTIVE ORGANS 221 Fig. 481. antheridium consisting of an incomplete wall and two internal cells, each of which gives rise to two antherozoids or male gametes; in the Phanerogams even this differentiation dis- appears. In Marsilea and Selaginella, the microspore gives rise to a small, somewhat oval multicellular body which pro- duces antherozoids in its internal cells. The fenaale gametophyte also shows a gradual degeneration. In Salvinia the megaspore bursts at its apex (fig. 481), and the prothallium is developed as a curiously shaped green bo
. A manual of botany. Botany. MORPHOLOGY OF REPRODUCTIVE ORGANS 221 Fig. 481. antheridium consisting of an incomplete wall and two internal cells, each of which gives rise to two antherozoids or male gametes; in the Phanerogams even this differentiation dis- appears. In Marsilea and Selaginella, the microspore gives rise to a small, somewhat oval multicellular body which pro- duces antherozoids in its internal cells. The fenaale gametophyte also shows a gradual degeneration. In Salvinia the megaspore bursts at its apex (fig. 481), and the prothallium is developed as a curiously shaped green body, the greater part of which remains within the spore. The free part bears the archegonia. In Selaginella and Isoetes the development is still more markedly en- dosporous. The prothaUiuiu is developed inside the mega- spore (fig. 482), which does not open till the former is well advanced; in some oases, indeed, until the archegonia are rnature and the oospheres, or female gametes which they contain, are ready for ferti- lisation. In the Phanerogams the megaspore is never ex- posed, and the prothallium or gametophyte is therefore always completely internal. In verj' rare cases it partly projects from the apex of the megaspore, but this is very exceptional. In the Gym- nosperms {fig. 483) it still consists of a large number of cells; while its morphological nature was not understood, it received the name endosperm, which still continues to be applied to it. In the Angiosperms the reduction is still ixiore complete. "When the gametophyte is mature, it consists of only a few cells or masses of protoplasm, some of which have no cell-wall {fig. 484). In the Gymnosperms the archegonia, usually several in number, are well developed, and are much like those of Fi'/. 481. Gametophyte produced by the megaspore of Salvinia. pro. Prothallium bearing r(, youug sporophyte. Alter Please note that these images are extracted from scanned page images that may have
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