PRESENT TENDENCIES OF MORPHOLOGY 279 



Besides, as Darwin has never denied the existence and the import- 

 ance of mutations, which he called single variations, so from his side 

 De Vries has never sought to destroy the theory of selection. 



Instead of operating slowly upon fluctuating individuals, it acts 

 upon species in process of formation. The struggle for existence 

 exists among mutations and among the forms from which they 

 proceed, as W. Hubrecht has very correctly observed in the clear 

 analysis that he has recently given of the ideas of his compatriot: 

 "Far from having undermined Darwin's Darwinism, De Vries has 

 completed, purified, and simplified it," and only those think otherwise 

 who combat Darwinism for other than scientific reasons, and at the 

 bottom of their hearts wish much evil to the demonstrations of De 

 Vries and to all other possible forms of the theory of evolution. 1 



Another interesting application of mathematics to the morpho- 

 logical sciences is presented by the study of hybrid forms. The laws 

 of Mendel, recently verified by De Vries, Tschermak, Bateson, etc., 

 carry the calculus of probability to the furthest limit. It will be 

 useless to insist longer upon the numerous and important problems 

 relating to morphological heredity whose solution depends on the 

 rational study of numerical data which are as numerous as possible. 



From all of these considerations we deduce at present a conclu- 

 sion of remarkable generality; to wit, that the natural laws of evo- 

 lution seem to enter into the movement toward physical laws which 

 has manifested itself for some time. They assume more and more 

 the character of static laws. Thus guided by the conducting line 

 of the theory of descent, subjected to the precise measure of a per- 

 fect mathematical exactness, and controlled at each instant by 

 the experimental method, morphology each day becomes more the 

 explanatory science par excellence of the world of organized beings. 

 Morphological phenomena are the translation, the tangible expres- 

 sion, the perceivable criterion of physiological experiments, and 

 the latter borrow all their interest from the morphological mani- 

 festations which they engender. 



In connection with breeding and horticulture the morphologist 

 becomes in truth a creator. He is still more so when, in calling up 

 and grouping in thought the conditions under which living beings 

 are successively formed in the course of centuries, he perceives the 

 causal nexus which connects the new forms with those which have 



1 " I have purposely insisted on these points, because here and there a tendency 

 seems to prevail to look upon Darwin's views upon the origin of species as unsatis- 

 factory and obsolete and to proclaim the necessity of replacing them by broad 

 new hypotheses with which the name of De Vries should be coupled. These tend- 

 encies are in great favor with those that bear a grudge to the so-called Darwin- 

 ism for other than scientific reasons, and who in their innermost hearts would at, 

 the same time like to see a similar fate reserved for De Vries's demonstrations, and 

 even for the whole theory of evolution." A. A. W. Hubrecht, Hugo de Vries's 

 Theory of Mutations (The Popular Science Monthly, July, 1904, p. 212). 



