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 

 zoologists 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 



