346 BOTANICAL GAZETTE [October 



is no production of a new individual. The inference is that the 

 mutual attraction and fusion of two protoplasts is not all that is 

 necessary for reproduction, and that mutual attraction is as much 

 a secondary feature of sexual reproduction as is motility, and 

 simply directs motility. There must be some fundamental differ- 

 ence between an ordinary cell, therefore, and one that has matured 

 as an egg, but at the same time probably any protoplast may 

 mature as an egg. It seems fairly well established that whatever of 

 significance there may be in the sex act is found in the fusion of 

 nuclei. When two protoplasts fuse, therefore, and do not produce 

 a new individual, their nuclei must differ in some way from those of 

 functioning sperms and eggs. One may imagine the adjustment 

 of one nucleus to another before fusion can result in reproduction, 

 and this mutual adjustment probably lies at the basis of sex- 

 reproduction. It also probably explains the fact that sperms and 

 eggs vary in their ability to fuse, and in the results of fusion. 



Sexually differentiated individuals 



The appearance of male and female individuals may be regarded 

 as the extreme expression of sexual differentiation, which involves 

 much more than the differentiation of male and female gameto- 

 phytes, with their different sex organs. It is not necessary to 

 present illustrations of the various situations this differentiation 

 includes, for such a presentation would be merely a recital of life 

 histories very familiar to morphologists. When the life histories 



of sexual plants are considered, ranging from the algae to the 

 angiosperms, the following tentative conclusions are suggested: 



Gametes are necessarily differentiated physiologically, and 

 whatever explains this differentiation will explain the sexual differ- 

 entiation of individuals. It seems to be a differentiation in chemical 

 and physical constitution, which may or may not express itself in 

 bodies visible in the sexual cells. 



Whatever may be the cause of sexual differentiation, it is capable 

 of being transmitted through generations of vegetative cells, until 

 conditions favor its expression in the form of gametes and their 

 associated structures. The implication of this statement is that 

 sexuality does not arise de novo when gametes appear, but that 



