532 



THE AMERICAN NATURALIST [Vol. XLIV 



To the writer the differences between the egg and the 

 spore appear to be such as may depend primarily on a 

 greater vigor and vitality given to the egg by the fusion 

 of the gametes, a vigor which has expressed itself in such 

 varied morphological manifestations because of the dif- 

 ferent conditions under which the sporophyte generations 

 have become established in the numerous phyla char- 

 acterized by their presence. The conditions affecting the 

 sporophyte are not alone those of physical environment ; 

 there are also those evolutionary factors that operate to 

 adjust the plant, as far as is possible, to its place among 

 other organisms. One conclusion stands out clearly 

 among the difficulties of these problems : as in the case of 

 sex, the sporophyte has probably arisen independently a 

 number of times in the evolution of plants. 



So we are brought to the end of our discussion of the 

 nuclear phenomena of sexual reproduction in the algae to 

 the problems of the origin of the sporophyte and the re- 

 lations of the sexual and asexual generations to one 

 another, whether or not they are essentially homologous 

 or antithetic in the alternation of generations. It is not 

 ■the purpose of this symposium to consider these matters, 

 but allusions and inferences could not be kept out where 

 the vital connections between the subjects under consid- 

 eration and these larger speculations are so close. The 

 immediate need of such discussion is perhaps not so great 

 for the reason that the pages of the New Phytologist for 

 1909 have presented two important papers of Lang and 

 Blackmail representing the opposite schools together with 

 a report of a discussion in which a number of the leading 

 British botanists took part. That the writer's sympathies 

 are strongly with the hypothesis of antithetic alternation 



of this paper. 



