. Fecundation in plants. Plant embryology; Plants, Sex in; Karyokinesis. THE EMBRYO-SAC OR FEMALE GAMETOPHYTE. 171 rise to the axial row of four cells, correspond, as in other Gymno- sperms, precisely with the first and second divisions in the microspore mother-cell of this plant. In my own opinion the only legitimate conclusion to be drawn from this morphological and cytological evi- dence is that the macrospore mother-cell of Larix is homologous with that of Helleborus and other Angiosperms in which the embryo-sac develops similarly. In the development of the embryo-sac, as typified by Lilit
. Fecundation in plants. Plant embryology; Plants, Sex in; Karyokinesis. THE EMBRYO-SAC OR FEMALE GAMETOPHYTE. 171 rise to the axial row of four cells, correspond, as in other Gymno- sperms, precisely with the first and second divisions in the microspore mother-cell of this plant. In my own opinion the only legitimate conclusion to be drawn from this morphological and cytological evi- dence is that the macrospore mother-cell of Larix is homologous with that of Helleborus and other Angiosperms in which the embryo-sac develops similarly. In the development of the embryo-sac, as typified by Lilitim and many other monocotyledonous plants, the hypodermal cell does not produce an axial row of four cells, but becomes at once the functional macrospore. With the growth of the nucellus this hypodermal cell increases greatly in size, as does also its nucleus (Fig. 71). The nucleus, after its characteristic period of growth, divides heterotypically. The two resulting daughter-nuclei lie in the ends of the cell. No cell-division follows this nuclear division, although the thickening of the connecting fibers in the equatorial region seems to indicate that a tendency toward cell- division existed (Fig. 72, A). The macro- spore continues its growth, and the daughter- nuclei divide. This division is homotypic and coiTesponds exactly to the second mitosis in the pollen mother-cell. The four resulting nuclei have, as a rule, the orientation shown in Fig. 72, B. Very frequently no vacuole is present at this stage, and the four nuclei are connected with each other and with the plasma membrane by systems of kinoplasmic radiations and connecting fibers. The increase of the cell in length is now rapid, and, as a result, one or more large vacuoles are formed at the center or near the micropylar end of the sac. Two of the four nuclei which are sisters move into the upper, and the other two into the lower end of the cell. In normal cases the nuclei in each end divide so that a group of four n
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