. The classification of flowering plants. Plants. 56 FLOWERING PLANTS [CH. cytoplasm. The mature male cell, which is visible to the naked eye in Zamia, is oval in form, broad and naked behind and spirally coiled in the anterior half with many short motile cilia emerging from the groove. These male cells are physio- logically comparable with the antherozoids of the Ferns, but represent morphologically the antherozoid mother-cells which themselves pass over into motile male cells and do not as in the Ferns develop such in their interior. They are homologous therefore to the non-motile male cells
. The classification of flowering plants. Plants. 56 FLOWERING PLANTS [CH. cytoplasm. The mature male cell, which is visible to the naked eye in Zamia, is oval in form, broad and naked behind and spirally coiled in the anterior half with many short motile cilia emerging from the groove. These male cells are physio- logically comparable with the antherozoids of the Ferns, but represent morphologically the antherozoid mother-cells which themselves pass over into motile male cells and do not as in the Ferns develop such in their interior. They are homologous therefore to the non-motile male cells of the other Seed-plants. In fertilisation the end of the pollen-tube, containing the tube-nucleus and the sperm-cells, grows towards the embryo- sac (fig. 7); the turgid end of the tube bursts and discharges its contents into the liquid of the chamber above the archegonia, towards the necks of which the sperm-cells swim, and make their way down to the large egg-cell. As the male cell passes into the cytoplasm of the oosphere its own cytoplasmic membrane with the ciliated band slips off and remains in the peripheral region of the oosphere, while the nucleus moves on and fuses with the female nucleus. Fig. 7. Longitudinal section of upper end of nucellus in Zamia integrifolia just before fertilisation; enlarged. The ends of three pollen-tubes, on which the remains of the pollen-grain wall can still be seen, are growing down into the archegonial chamber, n. c, pollen-chamber; t, pollen-tube which has penetrated the nucellus ; 0, oosphere; p, prothallium. (After Webber.) In the development of the oospore a pro-embryo is first formed. The oospore-nucleus divides repeatedly and a parietal layer of cytoplasm is formed containing numerous nuclei, between which cell-walls subsequently appear, forming one or two parietal layers of cells surrounding a central cavity caused by the disorganisation of the internal cytoplasm and nuclei (fig. 8, A). At the base of the pro-embryo the cells ar
Size: 1841px × 1357px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectplants, bookyear1904
