Oenothera Scintillans. 381 



by a very definite selection resulting from the fact that 

 scintillans is much more delicate than Lamarckiana. 



It is now sufficiently clear that a species which pro- 

 duces besides offspring like itself other constant types 

 must inevitably disappear sooner or later. 



If the constant types appear in a smaller proportion 

 than we have considered so far, in each generation, as in 

 the case of 0. scintillans producing 70 % of its kind 

 (p. 246) it will take longer for the form to disappear; 

 but disappear it must.^ It is only by excelling its con- 

 stant offspring in individual strength that it can ever 

 stand a chance of surviving altogether. If it did this 

 it would be in the position in which 0. Lamarckiana 

 finds itself now with regard to the new species arising 

 from it. 



These facts give a simple explanation of the absence 

 (or perhaps rather the great rarity?) of inconstant spe- 

 cies in nature. For it is not necessary to assume that 

 such do not arise or even that they do not arise often. 

 The proof that they cannot maintain themselves is suf- 

 ficient. Left to themselves the}^ will be reduced in a 

 very few years to a hundredth or even thousandth part 

 of the total of their offspring, and they will very soon 

 be lost altogether. They can only continue to exist by 

 being produced continuously or, at least, frequently by 

 the parent species. 



The mutation theory renders the origin and disappear- 

 ance of unfit types intelligible ; moreover the actual origin 

 of such has been observed. These cases constitute an 

 insuperable obstacle in the way of the theory of selec- 

 tion. 



* The I2th generation will bring the form down to about i % ; 

 and generally speaking the xth to (Vio)''. 



