770 THE AMERICAN NATURALIST. [Vol. XXXV II. 



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 bv 

 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 t(j time to account 

 for the origin of species, but to bring under consideration the 

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

 discontinuous variation have been based by deX'ries. 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 GEnothera 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 

 accounting for the existence of any single species has not been 

 proven with the finality offered by the evidence of discontinuous 

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

 been demon.strated to have arisen by mutation, some are known 

 to have arisen as the result of hybridization, and that evidence 

 has been accumulated which has been interpreted to demonstrate 

 the origin of species by natural selection, and by adaptation. 

 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. 



NkU \()RK HoTANKAI. (JARDEN, 



August, 1903. 



