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 spermatozoón brings 
to the egg the agent of cell division as a centrosome. The 
investigations of several zoölogists 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, : oo, 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 à centrosome or centrosphere. Of course the kinoplasm 
which lies immediately without the nuclear membrane of the 
investing layer around the fusion nucleus. It is reasonable to 
Suppose that the mixing of these masses of kinoplasm with the 
