MUTATION THP:()RY OF PROFESSOR DE VRIES. 637 



must be prepared to admit who accepts the proposed mutation theory. 

 I may add that for reasons which I will state further on I am much 

 inclined to view this theory with fav'or, but the affirmative manner in 

 whicii J present this sketch of it may be regarded as indicatino- my 

 purpose to discuss the subject from the author's standpoint. 



This theory does not require that one should go l)ack to the view 

 held by devout naturalists before Darwin's time, that species are cate- 

 gories of creative thought in the Divine mind, but it does require that 

 one shall regard species as having a more real entity than he has been 

 accustomed to conceive of in connection with the theory of natural 

 selection. Professor de Vries expressly claims that nnitation, although 

 suddenly accomplished, is strictly a physiological process, coincident 

 in its incipient manifestation with the function of reproduction. It is 

 therefore plain that his theory does not in any way oppose the funda- 

 mental fact of evolution, but offers a new theoretical explanation of 

 the method of its accomplishment. 



Considering the completeness and success of the experimental studies 

 made b}- Professor de Vries with (Enotheyxi^ one naturally infers that 

 other plants also now exist in the fullness of their mutative period, 

 and that these would 3aeld similar results under similar treatment. 

 Perhaps, also, certain species which are immutable in some regions 

 will be found to be mutable in others. Indeed, results that evidently 

 belong in the same category with those obtained by Professor de Vries 

 have, from time to time, been obtained by naturalists and horticultur- 

 ists from various plants, but those cases have not hitherto received the 

 interpretation that will be given to them by the mutation theor}'^, 

 although they were known to be incompatible with the theory of nat- 

 ural selection. I have lately recordecl a case of this kind,'' and several 

 others have more or less fully engaged my personal attention. 



Professor de Vries is confident that his theory is as applicable to 

 animals as to plants, and that conclusion is plainly a logical one; but 

 he makes no suggestion as to methods of experimental studies of that 

 kind, and 1 can make none. I have, however, in my paleontological 

 studies, been often confronted with facts with relation to both animal 

 and vegetable fossil forms that seem to be quite inconsistent with the 

 theory of their origin by the slow process of natural selection. Dem- 

 o.istrations of the truth of the mutation theory must, of course, always 

 1)6 made with living organisms, but as much of its support mustdou))t- 

 less come from apriori reasoning, especiall}^ with reference to extinct 

 organic forms, I will close b}- mentioning a few of the many paleonto- 

 logical facts referred to. These seem to relate with peculiar force to 

 the primary proposition of the mutation theory, that all species have 

 originated from one another suddenly, and not by slow degrees; and, 

 also, to two of its secondary propositions. The first of these two is, 



''See "Science," Vol. XVI, n. s., Nov. 29, 1901, pp. 841-844. 



