166 BOTANICAL GAZETTE [march 



egg in Nephrodium accords with Thom's and Shaw's accounts. The 

 presence of the resting nucleus including both maternal and paternal 

 chromatin within a common nuclear membrane as described in 

 Nephrodium was also described by Ikeno (43, 44) in Cycas and 

 Ginkgo, these two being the only forms among Cycadales and Ginkgo- 

 ales in which fertilization has been traced to the complete union of the 

 two gamete nuclei. 



There is only one paper that gives details of fertilization in a 

 bryophyte, a contribution by Kruch (56) on Riella. In this form 

 he states that after the sperm enters the egg, a male nucleus is organ- 

 ized which increases in size until it is about equal to the egg nucleus. 

 This differs from the condition in Nephrodium, for the sperm does 

 not enter into the egg nucleus, but two nuclei fuse side by side with 

 their chromosomes fully organized. 



With respect to the cytoplasmic structures of the sperm, all inves- 

 tigations among cycads and in Ginkgo agree that they are left behind 

 in the cytoplasm of the egg before the gamete nuclei unite. A similar 

 condition is reported in both Adiantum and Aspidium. In Nephro- 

 dium the author cannot confirm the foregoing view, since cases were 

 observed in which the blepharoplast was not left behind in the cyto- 

 plasm. However, such cases do not of course necessarily mean that 

 this structure takes part in what may be regarded as an essential part 

 of the process of fertilization. 



Conclusion 



Since the present investigation on spermatogenesis, oogenesis, and 

 fertilization, together with the preceding study on sporogenesis, has 

 been made to trace out the complete history of the chromosome in 

 the normal life-cycle of Nephrodium as preparatory to the study of 

 apogamy, the general conclusions will be given in the subsequent 

 paper. However, the two principal points established by the present 

 investigation may be stated here: (1) the counting of the number of 

 chromosomes is possible in the gametophyte; (2) the number of the 

 chromosomes in the gametophyte is constant (64 or 66). 



In closing I wish to express my thanks to Professor John M. 

 Coulter and Doctor Charles J. Chamberlain who gave important 

 advice and valuable suggestions in the course of the study. 



