MUTATION AS RECENTLY EXPOUNDED BY DE VrIES. 77 



21 . Mutation as recently expounded by De Vries. 



As "Species and Varieties, Their Origin by Mutation," by De Vries, 

 1905, has appeared while the present volume is being put into type, I 

 add a few words on the very interesting experiments there described. 

 In his first lecture he fully endorses Morgan's interpretation of the 

 mutation theory and speaks of the lectures that are to follow as "a 

 review of the facts obtained from plants which go to prove the asser- 

 tion that species and varieties have originated by mutation, and are, 

 at present, not known to originate in any other way." (See p. 9.) 

 The experiments described in Lecture XIX show that I^amarck's 

 evening primrose, as it now exists in Holland, is subject to mutation; 

 for over two per cent of the seed taken without selection from plants 

 that have been grown without crossing and in rich soil for two or three 

 generations, produce clearly marked digressions from the original 

 stock. About half of these mutations produce the variety with ob- 

 long leaves, while the remaining half produce several other types. 

 (See p. 556.) In all, twelve new types have been observed, of which 

 nine are entirely constant as long as they are kept isolated, and three, 

 though kept unmixed, produce both the original type of the species 

 and the new type. His record indicates that selection has not been 

 used in producing these results ; but how different are the facts given 

 in the production of the double-flower variety of the corn-marigold. 

 His description indicates that careful selection, during successive 

 generations, of seed from flowers furnishing the largest number of 

 ray- florets brought the average number of these rays up to 2 1 in the 

 third generation, to 34 in the sixth, to 47 in the eighth, and to 55 in 

 the ninth generation. In the seventh generation three heads were 

 produced with a few rays in the midst of the disk; in the eighth 

 generation the maximum number of rays (counting both internal 

 and external ones) was 100, in the ninth generation 200. "All the 

 children of this original mutated plant [the plant producing the three 

 heads just mentioned] showed the new character. * * * jv^Qt 

 on all the heads, not even on the majority of the heads on some 

 individuals, but on some heads all gave clear proof of the possession 

 of the new attribute." (See p. 504.) My only suggestion is that 

 since the selection of fluctuating variations for six generations was 

 necessary in order to reach the new character which is called a 

 mutation, and for three more generations in order to perfect the 

 type, selection should be regarded as a part of the process produc- 

 ing the new type. On pages 468-478 he describes another experi- 

 ment with another species, commencing with successive selections of 



