256 THE AMERICAN NATURALIST. [Vol. XXXIX. 



of the origin and evolution of the endosperm in angiosperms 

 there is some evidence in favor of the second possibiUty. 



Strasburger (:00b) holds that the double and triple nuclear 

 fusions in the embryo sac are not true sexual acts even though 

 they may involve an important principle of fertilization, namelyl 

 a stimulus to growth. According to him, sexual processes pre- 

 sent two distinct features which he designates as " generative 

 fertilization " and " vegetative fertilization." Generative fertili- 

 zation deals with the mingling of ancestral hereditary substances 

 in the nuclei and establishes the basis for such characters as 

 hold the species true to its past or introduce new qualities as 

 variations into the germ plasnv. Vegetative fertilization brings 

 to the fusion nucleus simply a stimulus to growth such as may 

 be given to unfertilized eggs by changes in their physical and 

 chemical environment. We might apply this classification to 

 many of the examples of asexual nuclear fusions which we have 

 discussed, as in the apogamous development of the fern and the 

 origin of the paired nuclei in the rusts, and they have the ele- 

 ments of vegetative fertilization in Strasburger's sense. But 

 such distinctions are very subtle and it seems rather doubtful 

 whether they add much to the clearness of our conceptions. 

 The growth stimulus of "vegetative fertilization" is always 

 an accompaniment of " generative fertilization " and would be 

 expected of any cell unions or nuclear fusions. The pecul- 

 iarities of sex lie in the phylogenetic features of the phenomena, 

 i. e., in the union of differentiated gametes . with their long evolu- 

 tionary history and not in the mere fusion of any nuclei at any 

 time. 



From this point of view the double fusions of polar nuclei or 

 the triple fusions, when a sperm nucleus becomes involved in 

 the phenomenon, are of very doubtful sexual nature since no 

 phylogenetic connections have been established with the normal 

 sexual processes of the spermatophytes. Indeed, there are many 

 irregularities in the process of endosperm formation which com- 

 plicate the discussion and make it very difiQcult to trace relation- 

 ships. Thus nuclear fusions are described in the late stages of 

 endosperm formation when several of the free nuclei become 

 included in the same cell area by the formation of the cell walls 



