SIGNIFICANCE OF THE SEXUAL PROCESS. 59 
their greatest value in the suggestiveness of their results and the new 
points of view to which these results lead. They do not show that 
the reactions brought about by these stimuli are the same as those 
resulting from the union of sexual cells. Although the development 
of a rudimentary embryo induced by artificial means may proceed in 
the same manner as the product of normal fecundation, yet the arti- 
ficial stimulus cannot be looked upon as being equivalent to the sexual 
process. In the case of the former, we are dealing with a stimulus 
which merely starts growth, but a mature individual is never developed. 
The sting of an insect or some similar stimulus may call forth a 
growth in a leaf of an oak, which results in a gall, a local and limited 
growth, but never in an oak tree, and we cannot for one moment 
think of comparing such a stimulus to a sexual process. 
The author does not agree with those who regard the sexual process 
merely as a restoration to the egg of the power of growth and division. 
We are not quite ready to lay aside, as yet, the facts won by twenty 
years of the most careful morphological research for any chemical or 
electrical theory of heredity. 
Our knowledge of sexual reproduction in the plant kingdom indi- 
cates beyond question that that which is of primary significance in the 
sexual process is the fusion of the nuclei, and the question still 
remains, which imparts the growth stimulus, the nucleus or the cyto- 
plasm of the sperm? Or are both necessary? 
Strasburger has suggested that the stimulus to growth and division 
is given by the cytoplasm, and especially a particular part of the same, 
the kinoplasm, brought into the egg by the spermatozoid. Some 
zoblogists have attributed this stimulus to the centrosome of the sperm, 
but in the plant kingdom no case is definitely known in which a 
centrosome is brought into the egg by a spermatozoid. The doctrine 
of Strasburger is perhaps the best that has been proposed, and it seems 
to have some basis in fact. According to this view the egg is rich 
in food material, trophoplasm, and poor in kinoplasm, while in the 
sperm the reverse obtains. The unfecundated egg is incapable of 
developing, therefore, on account of the lack of energy. 
This theory, however plausible it may seem, leaves much to be 
desired. In the first place, it is not known as a fact that the egg is 
poor in kinoplasm, and that the sperm is correspondingly rich in that 
substance. In many cases the quantity of cytoplasm of the male cell 
is so small that it seems almost incredible that it could have such a 
powerful influence. The spermatozoid of the fern, for example, con- 
sists of a relatively very small amount of cytoplasm, and the kino- 
plasmic part of this constitutes an organ of locomotion. Although 
