146 THE THEORY OF MUTATION 



which have been published by de Vries are brought 

 to our notice, we are naturally disposed to reserve our 

 acceptance of the conclusions which they seem to indi- 

 cate until observations have been made in confirma- 

 tion of them by some competent observer. This has 

 now been done by Professor MacDougal at the New 

 York Botanic Garden.* MacDougal has carried out 

 observations similar to those above described upon 

 the offspring of seeds sent by de Vries from Holland, 

 and with closely similar results. Thus he has observed 

 all the new forms which de Vries described, as well as 

 some additional ones ; and he has obtained an even 

 higher percentage of ' mutants ' than de Vries him- 

 self namely, about 3 per cent, of the total number 

 of seedlings grown. This last result is probably only 

 due to the application of more thorough methods of 

 investigation, and to a smaller mortality of the weakest 

 plants, arrived at by greater care, and rendered pos- 

 sible by the warmer summer climate and by American 

 efficiency in method. De Vries himself, in one of his 

 later generations, when particular care was applied to 

 the methods of cultivation, obtained nearly 3 per cent, 

 of new forms. MacDougal also states that he has 

 observed undoubted cases of mutation taking place 

 in other species besides (Enothera Lamarckiana. 



It appears, then, that there can be no doubt about 

 the genuineness of the phenomenon described by de 

 Vries. But it is, of course, quite a different thing to 

 assert that all natural species arise in this fashion, and 

 this is what de Vries' theory, as distinguished from 



* Reference should also be made to the work of R. R. Gates ; 

 see his ' Mutation Factor in Evolution/ 1915. 



