142 



ARCHEGONIATES. 



able in the sperm-nucleus varies greatly in different individuals. In 

 some cases the sperm-nucleus, after two days, showed no further 

 advance than was observed in others after only thirty-six hours. As the 

 reticulation of the sperm-nucleus continues, its structure becomes looser 

 and more open, and its cork-screw shape disappears (Fig. 56, D, E). 

 As far as is known at present the reticulation of*lhe sperm-nucleus 

 continues until its network is no longer recognizable from that of the 

 egg when fecundation is complete. 



During the process of fusion it will be seen that the sperm-nucleus 

 goes through the same series of changes as in the development of the 

 spermatozoid, but in the reverse order. The time elapsing between 

 the entrance of the sperm-nucleus into the egg and complete fusion 

 may vary considerably in individual cases. 



In Pilularia globulifera, according to Campbell ( 5 S8), the sperm- 

 nucleus assumes a loose and more granular structure, and rounds up 

 before penetrating or uniting with the nucleus of the egg. Judging 

 from Campbell's figures, it seems that in Osmunda (Campbell, '92) 

 the sperm-nucleus, as in Onoclea, enters the nucleus of the egg before 

 undergoing any visible change in form or structure. 



In this respect certain ferns are without parallel in the plant king- 

 dom, except, perhaps, in the Gymnosperms, and it would be inter- 

 esting to know how widely distributed the phenomenon is in the 

 Pteridophyta, and whether it occurs in any other plants. 



GYMNOSPERMS. 

 CYCAS, ZAMIA, AND GINKGO. 



THE MALE GAMETOPHYTE. 



The development of the spermatozoid in Cycas (Ikeno, '96, '98), 

 Ginkgo (Hirase, '96, '98; Webber, '97; Fujii, 1900), and Zamia 

 (Webber, '97, 1901), bears a striking resemblance to that in the fern, 

 especially in regard to the origin and behavior of the blepharoplast. 

 There seems now to be no doubt that the blepharoplast in these three 

 genera is homologous to the blepharoplast of the fern, and, in fact, the 

 entire development of both sexual cells indicates with a certainty that 

 these gymnosperms bear a close phylogenetic relationship to the 

 pteridophytes. 



Since the development of the spermatozoid in Cycas and Zamia 

 differs in certain important details according to the two investigators, 

 Ikeno and Webber, a somewhat detailed account of the process will be 

 given for both genera, while Ginkgo will be referred to for comparison. 



