140 THE THEORY OF MUTATION 



his facts, amounts to. De Vries made observations 

 upon a large proportion of the plants of his district 

 by the method of growing great numbers of their 

 seedlings, but he failed to find the same phenomenon 

 going on in any of them. He therefore supposes that 

 species are subject to comparatively short periods of 

 mutability which recur at relatively long intervals, 

 and that all the species he examined except the 

 (Enothera were in this intermediate staple period of 

 their existence. Direct proof of this suggestion is 

 naturally out of the question. 



It will be well to summarize briefly the conclusions 

 at which de Vries has arrived, as the result of his 

 observations upon (Enothera. 



The following are the points to which he attaches 

 chief importance : 



1. The new species arise suddenly at a single step, 

 without transitional forms. 



2. They are usually fully constant from the first 

 moment of their origin. 



3. The distinctive characters of the new forms agree 

 in kind with those which distinguish from one another 

 such old and established species allied to (Enothera 

 Lamarkiana as 0. biennis and 0. muricata. Only one 

 of the new forms namely, 0. nanella, a dwarf type 

 is analogous with any ordinary kind of variety of 

 garden origin. 



4. A considerable number of individuals of the same 

 sort usually make their appearance at the same period. 



5. Although the new types vary in a normal fashion, 

 and frequently transgress the limits dividing them 



