No. 495] 



COXSTAXCY OF MUTAXTS 



175 



and stockmen of the right to hope for the adjustment of 

 a species to new surroundings in which at first it does 

 not fit. 



It is hard to comprehend a philosophy which recognizes 

 the old conception of species yet breaks it into countless 

 " elementary species," and at the same time claims abso- 

 lute constancy for the characters of the elementary forms. 

 If mutations, which all agree may occur, do not come from 

 irritations of environment, internal or external, from 

 what cause may they arise? Must we say that each plant 

 with an observable unit character is a species and, with 

 Linnaeus, that it always was? My observations do not 

 allow of this thought; neither have I ever seen an acci- 

 dent in nature. The only observed accidents of nature, 

 when known, have always been found to have direct nat- 

 ural causes. I could not work with faith upon plant breed- 

 ing if I could convince myself that any plant was ever 

 the result of an accident. 



The fact that plants mutate and that new types arise 

 in regular mathematical relations due to cross breeding, 

 and that selections from individuals give the correct 

 methods of breeding, seems evident, but I have seen noth- 

 ing to convince me of absolute constancy of either indi- 

 vidual or species. Mutation seems to be just a good name 

 for a grade of natural changes and no more. We have 

 still to look for the causative feature in the environment 

 behind the mutation or change of character; and, if we 

 wish to improve upon agricultural species or varieties or 

 individual strains, we must select from among the occur- 

 ring changes, whether we call them mutants, elementary 

 species or unit characters. The demonstrations of mu- 

 tations and the new knowledge that arises from a better 

 understanding of the laws governing union of and correla- 

 tion of characters must eventually greatly facilitate the 

 studies looking toward an understanding of direct special 

 causes for the changes which occur in the evolution of a 

 type. DeVries' original experiments were of immense 

 value, but I believe his philosophy of constancy to be 



