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ever increased until the last word in this discussion may perhaps 

 be for the physiologist alone. The great question involved in 

 the Mutation Theory is the old, old problem of the origin of spe- 

 cies, a very considerable advance in which has been made by de 

 Vries and those who were stimulated by his work. It is quite 

 wrong to suppose that he has controverted the general results 

 of Darwin's work ; he has supplemented it, brought it within the 

 range of more conclusive proof. 



As the Linnaean or collective species may be regarded to-day 

 they are usually separable into several more or less distinct 

 strains which show no intergrading forms, and the diagnosis of 

 any one species is, so to say, the average impression of them. 

 To these distinct strains de Vries has given the name elementary 

 species, and according to his interpretation they are the really 

 discrete, finally segregable units, between which no intermediate 

 types exist and concerning the origin of which we are really 

 concerned. It matters not whether it was through ignorance or 

 simply from convenience that the earlier taxonomists grouped 

 many of these forms into a single species ; we must conclude, 

 that in general species, as recognized by the books, are quite 

 artificial. It matters not, also, what we call these finally not 

 further resolvable forms. Therefore let us accept de Vries's ter- 

 minology and use the term elementary species ; the real point 

 of the inquiry is how did these forms arise. It is upon this that 

 de Vries's work has thrown a great light. He has shown that 

 they may arise suddenly and without previous preparation from 

 preexisting forms, in which case the elementary species may be 

 termed mutants, and the theory which has to do with the inves- 

 tigation of their origin the Mutation Theory. 



The next task then is to examine more closely the methods 

 which de Vries employed, the evidence which he has to support 

 his views, both as to the observations on the origin of these 

 mutants and their behavior after they have come into being, and 

 further, what success subsequent investigators have had in sup- 

 porting de Vries's evidence, and how far they have extended his 

 conclusions. In the first place, it may be remarked that the 

 conclusions as first published in 1901 and 1902 were not the 



