Proceedings of the Ohio State Academy of Science 343 



make any decided claims. But it may well be that the sex is 

 determined at the tirst division without any definite shifting of 

 hereditary characters. The anomalous cases can also be ex- 

 plained as examples of abnormal latency or activity. Probably 

 with a large number of ctiltures properly controlled, one could 

 find tetrads giving rise to all males or all females. One can 

 simply say that in Sjjhaerocarpus sex determination is usually 

 coincident with reduction. To say that it is caused by a definite 

 segregation during reduction of male and female hereditary 

 units is another proposition. Closely related Bryophytes are 

 hermaphrodite after reduction. It must be clearly kept in mind 

 that when plants finally developed a condition of complete uni- 

 sexualitv in the heterospores groups it was accomplished with- 

 out any reference to a segregation in the reduction division. 

 This is the one great fact that stands out most prominently. 

 The final evolution of a definite sex determining process was ac- 

 complished independently of the reduction division and there- 

 fore inrlependently of any known segregation of material heredi- 

 tary units or determinants. Alaternal and paternal chrorro- 

 somes do not determine sex whatever determining factors may 

 be present, the only visible and known dift'erence in the male 

 and female producing microspores and megaspores of higher 

 plants is a difi^erence in size of the cell together with a dififer- 

 ence in the amount of cytoplasm and included food materials. 

 If it can be shown that sex is determined independently of re- 

 duction in a large number of cases then it is reasonable to de- 

 mand that the opposite assertion be established with indubitable 

 proofs. 



Not only does the double or single number of chromosomes 

 appear to have nothing to do with sex determination, but ac- 

 cording to Yamanouchi, the apogamously produced sporophyte 

 of nephrodium, which shows constantly the x or gametophytic 

 number, looks like the ordinary 2x or diploid sporophyte. result- 

 ing from fertilization. It is evident, therefore, that the single 

 or double number has little influence upon the general appear- 

 ance of the plant. The conclusion follows that both the mater- 

 nal and paternal chromosomes have all the ordinary hereditary 



