i 9 o8] YAMANOUCHI— APOGAMY IN NEPHRODIUM 311 



touch any cvtological particulars. Since the announcement of Stras- 

 burger's view of the antithetic origin of alternation, the first to be 

 based on cvtological details, chief attention has been directed by many 

 workers to the behavior of chromosomes during the reduction division 

 in the normal life-cycle. As to the results of such accumulated studies, 

 the various views arc not readily grouped. However, the majority of 

 cases confirms the view that the periodic reduction of chromosomes 

 is necessary; in other words, the gametophyte with the x number 

 of chromosomes is entirely distinct from the sporophyte with the 2X 

 number, and the transition from one generation to the other is marked 

 by the reduction of chromosomes in sporogenesis and the doubling 

 of chromosomes in fertilization, in connection with which the pre- 

 dominant characteristics of one generation are entirely lost and the 

 potentialities of forming the other generation are regained. 



As stated above, the cytological work on apogamy and apospory has 

 been chiefly among flowering plants; and quite recently our knowledge 

 concerning these phenomena in ferns was extended by the contribution 

 of Farmer and Digby (24) on Lastrea, Athyrium, and Scolopendrium, 

 and of Strasburger (68) on Marsilia. According to these investi- 

 gations, apogamy, whatever its cause may be, is always preceded 

 either by apospory or the fusion of two vegetative nuclei, which seems 

 to favor the view that the 2X number of chromosomes is necessary to 

 establish the sporophyte. Apogamy and apospory, which have been 

 the chief argument for the theory of homologous origin, now seem to 

 support the theory of antithetic origin. 



As a matter of fact, the nuclear condition in Nephrodium in the 

 normal life-cycle confirms the antithetic theory; but apogamy in 

 Nephrodium introduces a new situation. In this case apogamy 

 is preceded neither by apospory nor fusion of vegetative nuclei, but 

 the sporophytes are developed with the haploid number of chromo- 

 somes. If it might be questioned whether the situation in Nephro- 

 dium— in which the nucleus of the gametophyte with the x number 

 can establish the sporophyte — may favor the idea of homologous 

 origin, it must be remembered that we have such abnormal cases of 

 apogamy and apospory in flowering plants, where the embryo sac 

 (probably gametophytic) does not contain the characteristic x number 

 of chromosomes, but always the 2X number. 



