HERITABLE DIFFERENCES 41 



species. To this end he marshaled evidence in support of 

 the gradual transition of one species into another, 

 emphasizing fluctuating modifications rather than muta- 

 tions which seemed to him to play a minor role in the 

 origin of species. 



It remained for the Dutch botanist Hugo deVries to 

 be the first to analyze the character of mutations and 

 to focus attention upon them. There is something 

 distinctly suggestive of Darwin's method in the fact 

 that deVries worked in silence for twenty years before 

 he gave the world the "Mutationstheorie" with which 

 his name will be forever connected. 



2. A SUMMARY OF THE MUTATION THEORY 



The main features of the mutation theory of deVries 

 may be indicated as follows: 



a. New species arise abruptly regardless of environ- 

 ment without transitional forms, and at present they 

 are not known to arise in any other way. 



6. New forms arise as unusual deviations from the 

 parent form, which itself remains unchanged although 

 it may repeatedly give rise to similar deviations. 



c. New mutations are, from the first, constant, that 

 is, they produce their like. They do not become 

 gradually evolved as the result of natural selection 

 although natural selection may act upon them after 

 they appear. 



d. Among mutations there may occur forms char- 

 acterized by the addition of something new, progres- 

 sive elementary species, as well as forms lacking 



