170 The Origin of Species by Mutation. 



nized up to that time, were only varieties ^ And it will 

 obviously continue to be impossible to demonstrate the 

 origin of a "species" so long as this demonstration is 

 regarded as ''degrading" the form in question to the 

 rank of a variety. This would become a mere juggling 

 with words. 



The conception of a variety held by those who are 

 the best qualified to judge, rests on the view that a single 

 character is not sufficient to confer specific rank on a 

 given form. A beautiful example is afforded by the case 

 which we have already mentioned of Datura Stramonium 

 and Datura Tatula. Each was regarded as a species by 

 Linnaeus himself, but they have been united to form 

 a single species by more recent authors on the ground 

 that Tatula is only distinguished from Stramoniwn by 

 the possession of a blue pigment in its flowers, stem and 

 petioles.^ 



This limitation of the idea of a variety is manifestly 

 desirable scientifically, especially for the reason that the 

 distinguishing feature is very often due to the loss or 

 latency of a character: absence of Petals, of Hairs, of 

 Thorns, of Color in the flower and so forth. Such cases 

 afford the best examples of what we ought to call a vari- 

 ety. But it should not be forgotten that the evidence for 

 the relationship of such forms to their species ordinarily 

 rests only on analogy ; and not, or very rarely, on actual 

 proof. 



Such varieties are just as distinct and just as constant 

 in cultivation as the best species. If it is still considered 

 proper that they should be called varieties, then it fol- 



^ Wallace^ Darwinism, p. 87 



^ In my opinion, Siramoninm is regarded quite wrongly as the 

 species and Tatula as the variety. Every analogy points to the blue 

 as the older and the white as the younger form (See Fig. 5 on p. 31). 



