464 THE AMERICAN NATURALIST. [Vol. XXXIX. 



processes are involved in the sexual act. The first, termed 

 "vegetative fertilization," is simply the stimulus to growth 

 which results from the fusion of two nuclei or other masses of 

 protoplasm. The second, called "generative fertilization," in- 

 volves deeper factors than those of mere growth stimulus. 

 These lie in the union of germ plasm of diverse parentage with 

 the mingling of hereditary racial characters and individual varia- 

 tions and the establishment of a new organism which may have 

 possibilities of development quite different from the parent form. 

 The effects of " vegetative fertilization " may be imparted to 

 protoplasm artificially by chemical and physical stimuli as has 

 been done in the numerous experiments of Klebs and Loeb 

 on the conditions which induce parthenogenetic development. 

 "Generative fertilization" has a phylogenetic significance and a 

 background which is entirely apart from the mere vegetative 

 processes of cell growth and division. 



It is apparent that Strasburger's theory is open to the same 

 line of criticism that has been brought against the universal 

 application of Boveri's hypothesis that the spermatozoon brings 

 to the ^gg the agent of cell division as a centrosome. The 

 investigations of several zoologists indicate that one or both of 

 the centrosomes in the first cleavage-spindle may be derived 

 from the egg or may be formed de novo (see Wilson, : 00, pp. 

 196, 208). The kinoplasm of the plant sperm, whether in the 

 form of a blepharoplast or as an ill defined accompaniment of 

 the sperm nucleus has not been shown to take part in the forma- 

 tion of the first cleavage spindle. There is no evidence that the 

 blepharoplast- retains its organic entity in the egg to pass over 

 into a centrosome or centrosphere. Of course the kinoplasm 

 which lies immediately without the nuclear membrane of the 

 sperm, and there is sometimes a conspicuous amount of this 

 densely granular protoplasm, must merge with similar kinoplasm 

 associated with the egg nucleus at the time of fusion. For 

 example Miss Robertson (:04) and Coulter and Land (:05) 

 note in Torreya that the sperm nucleus brings to that of the egg 

 a large amount of accompanying kinoplasm which forms an 

 investing layer around the fusion nucleus. It is reasonable to 

 suppose that the mixing of these masses of kinoplasm with the 



