. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. REPRODUCTION, VEGETABLE (VEGETABLE OVUM). completely in their mode of germination. After lying a certain time on a damp surface, their inner cavities are found to be occupied by a number of small spherical cellules, each of which contains in its interior a spirally coiled fibre (antherozoid). By the dehis- cence of the valves of the external tegument, Fig. 179. Vulvate dehiscence of microspore of Selayinella hel- vetica, six months after sotciitg, showing escape of antherozoids, 300 dium. the antherozoa are set free; and
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. REPRODUCTION, VEGETABLE (VEGETABLE OVUM). completely in their mode of germination. After lying a certain time on a damp surface, their inner cavities are found to be occupied by a number of small spherical cellules, each of which contains in its interior a spirally coiled fibre (antherozoid). By the dehis- cence of the valves of the external tegument, Fig. 179. Vulvate dehiscence of microspore of Selayinella hel- vetica, six months after sotciitg, showing escape of antherozoids, 300 dium. the antherozoa are set free; and it is presumed, that it is by their agency that the archegonium is fructified, after the prothallium has been laid bare by the bursting of the macrospore at its apex. 90. RtrizocarpefE.—In describing the mode of reproduction of the Rhizocarpeae, we shall confine our attention to the genus Pilularia, respecting which the most exact researches have been made. 97. The macrospore of Pilularia is an egg- shaped body, presenting an equatorial constric- tion. It consists of an internal proper mem- brane (endospore), the so-called embryo sac, Fig. Section of macrospore of Pilularia some time after germination, 50 diam. a, two layers of the exospore, the outer, vertically striated, the inner, homogeneous; b, cavity of endospore bounded superiorly by the prothallium, the papilkcform summit of which projects through the canal of the exospore. which is surrounded by a white coriaceous exospore. This last exhibits two distinct layers, of which the internal is colourless and vitreous, without trace of structure ; while the external appears to be formed of prismatic columns fitting closely together, which are more distinct at the lower end of the spore, while they disappear entirely towards its smaller end or apex, at which point the exo- spore forms a papilliform projection open at its summit. From this arrangement there results a canal, which is immediately sur- rounded by the thi
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