No. 463.] STUDIES ON PLANT CELL.— VI. 467 
They are accompaniments of sexual processes which may always 
be expected but nevertheless are not the essential characteris- 
tics. The essence of the sexual act (fertilization) is the union of 
germ plasm with such possibilities of new developments as come 
from the inheritance of mixed characters from two lines of ances- 
try. And the more diverse and complex are the characters of 
the parents the more conspicuous are the essential features of 
the sexual act. Among lowly organisms and in simpler types of 
sexual processes the growth stimulus becomes exaggerated in 
our attention because the features of heredity are not so promi- 
nent as in the higher forms. But in the higher groups the 
varied characters of offspring express clearly the subtle factors 
concerned with the mingling of diverse germ plasm in the proc- 
ess of fertilization and the growth stimulus recedes into the 
background. 
For these reasons it seems to me that the term fertilization 
should only be used for the mingling of germ plasm with the 
possibilities of new combinations in the potentialities of the 
resulting sexually formed cell and that the growth stimulus should 
be treated as an accompaniment but quite apart from the essen- 
tials of the sexual act. And for these reasons I was careful to 
include in Section IV under the caption * Sexual Cell Unions 
and Nuclear Fusions" only illustrations in which the sexual 
nature of the phenomena was clearly shown by applying a mor- 
phological or phylogenetic test to the elements concerned in the 
process of cell fusion. The phylogenetic test seems to me the 
only sure way of determining the sexual nature of the members 
of a cell fusion and there are very few cases in which there can 
be any hesitation in deciding whether or not such elements are 
morphologically gametes. 
I included under “Asexual Cell Unions and Nuclear Fusions” 
in Section IV a number of cases in which the sexual nature of 
the act is under dispute for the reason that none of these satisfy 
the phylogenetic test. It is perfectly clear that the growth stim- 
ulus is a conspicuous feature of these cell and nuclear fusions. 
and that in this feature they resemble sexual processes but this 
mind, make them acts of fertilization or the 
does not, to my — 
nion of sporidia in the 
equivalent of sexual processes. The u 
