770 THE AMERICAN NATURALIST. [Vol. XXXVI L 



So far as the origin of mutations is concerned, it seems well 

 decided that the premutative alterations in seed-plants ensue in 

 the vegetative and sexual cells previously to the formation of the 

 embryo in which they first appear, and that no environmental 

 disturbances may bring about the alterations in question by 

 direct action on the seedling. 



It is not the purpose of this paper to discuss the various theo- 

 ries which have been put forward from time to time to account 

 for the origin of species, but to bring under c onsideration the 

 facts upon which the conclusions as to the origin of species by 

 discontinuous variation have been based by deVries. These 

 facts make inevitable the conclusion that new types of specific 

 rank, taxonomically separable, and physiologically distinct and 

 constant, without intergrading and connecting forms, have arisen 

 in CEnothera by discontinuous variation. That mutation is 

 the principal method of evolutionary procedure is not proven. 

 That natural selection is universally prevalent is certainly dis- 

 proven : that natural selection or any other method is capable of 



proven with the finality offered by the evidence of discontinuous 

 variation. It may be said, therefore, that species have actually 



Nothing in the nature of living organisms demands that all spe- 

 cies should have originated in the same manner, or that one 

 simple, or single method of procedure should have been followed. 



New York Botanical Garden, 

 August, 1903. 



