144 ARCHEGONIATES. 



after pollination each spore in the pollen chamber of the macrosporan- 

 gium germinates, the tube cell developing gradually into a branched 

 tube which penetrates the tissue of the nucellus. The tube-nucleus 

 passes into the tube, maintaining a position near the growing region 

 or end as long as the tube continues its growth into the tissue of the 

 nucellus, while the two prothallial cells retain their former position. 

 Contrary to the genus Pinus and other higher Conifers the distal end 

 of the tube does not grow directly toward the archegonia, but later- 

 ally and downward, serving especially as an organ for the absorption 

 of food (Fig. 65, A). The proximal end of the tube, carrying before 

 it the cap of exine, or the remaining outer wall of the spore, finally 

 grows toward the archegonium. The pollen tube has a similar beha- 

 vior in Zamia (Webber, '97) and Ginkgo (Hirase, '98). 



Soon after the germination of the spore the two prothallial cells 

 increase in size, especially the antheridial cell, which becomes spherical 

 (Fig. 57, B, / 2 ). Its nucleus is also correspondingly large, and the 

 cytoplasm presents a looser structure. In the meantime the anthe- 

 ridial cell divides, the daughter-nuclei being of equal size. According 

 to Ikeno ('98, p. 172) a wall is not formed between these two nuclei 

 in Cycasrevoluta. One of them now increases rapidly in size, so that 

 it occupies nearly the entire cavity of the mother-cell, while the other 

 remains small and is crowded out as a naked nucleus (Fig. ^7, C, D, 

 st) . The larger cell is known as the generative cell (Korperzelle of 

 the German literature) and gives rise to two spermatozoids ; the smaller 

 cell is the stalk cell (Fig. 57, C, D, st). 



As we shall see later Webber finds that the antheridial cell divides 

 regularly into the stalk and generative cells, but the plasma membrane 

 separating the two cells is delicate, and the stalk cell arches over the 

 first prothallial cell in such a manner as to give the appearance of the 

 latter being nearly enclosed by the former (Fig. 60, F, G). It is pos- 

 sible that the same is true also for Cycas. The plasma membrane, 

 being very delicate, may have been overlooked by Ikeno, for the posi- 

 tion of the two cells is such as to make it appear that the stalk nucleus 

 was forced out of the mother-cell. 



Soon after this stage of development two small bodies appear in the 

 generative cell (body-cell), lying close to the nucleus and on opposite 

 sides (Fig. 57, C, c}. Ikeno seems to be of the opinion that the two 

 bodies, which he calls centrosomes, are derived from the nucleus, for 

 the reason that just prior to their appearance outside of the nucleus, 

 objects staining similarly appear within the nucleus. These bodies, 

 which are the primordia of the blepharoplasts, move away from the 



