. A textbook of botany for colleges and universities ... Botany. SPERMATOPHYTES 215. consisting usually of two (fig. 478) or three cells, but in Podocarpus it sometimes becomes a massive structure of about twenty-five cells. There is no well-defined archegonial jacket, and when it is remem- bered that there is no special digestive zone about the mother cell, it is evident that the nutritix-e mechanism is not differentiated in this group as it is in Ginkgo, or even in the cycads. In the division of the nucleus of the ventral cell, which precedes the formation of the egg, there is no separating
. A textbook of botany for colleges and universities ... Botany. SPERMATOPHYTES 215. consisting usually of two (fig. 478) or three cells, but in Podocarpus it sometimes becomes a massive structure of about twenty-five cells. There is no well-defined archegonial jacket, and when it is remem- bered that there is no special digestive zone about the mother cell, it is evident that the nutritix-e mechanism is not differentiated in this group as it is in Ginkgo, or even in the cycads. In the division of the nucleus of the ventral cell, which precedes the formation of the egg, there is no separating wall formed, and hence no ventral canal cell. The ventral nucleus is its only representative, and in Torreya it is doubtful whether even this appears. The disappearance of the ven- tral canal cell and its nucleus is the last stage in the reduction of the axial row, which thereafter is represented only by the egg- Male gametophyte. â In the development of the male gametophyte, the podocarps and taxads show a striking contrast. In the r-^ 478.â Young arche- podocarps two to six vegetative (prothallial) gonium of Torreya, showing the cells appear (fig. 480); while in the taxads '^° '^'"'^ '^'^"^ ""^^ *^ <=â¢"^^' â ,7 , , ,⢠, cell. âAfter Coulter and no vegetative cells have been discovered, l^j^j. The division of the generative (primary spermatogenous) cell into the sterile stalk cell and the body cell is as described for the preceding groups (fig. 480); but a striking change appears in the fact that there' are no blepharoplasts in the mother cell, which means that ciliated (hence swimming) sperms are not formed. The nucleus of the body cell divides, and this division may be accompanied by a separating wall, so that two sperm mother cells are formed (taxads); or the nuclear division may not be accom- panied by wall formation, so that there are only two mother cell nuclei in the general cytoplasm of the body cell (podocarps). In either case
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
