Oenothera Scintillans. 379 



event is dependent not only on the quality of the varia- 

 tion but also on the environment in which it is placed. 

 The variations which pass through the sieve of the 

 struggle for existence are not different from, but merely 

 part of, those which are put into it. 



The mutation theory admits of the production of 

 such forms as will sooner or later for some reason or 

 other, perish without having contributed materially to 

 the flora or fauna of a district. The causes of such dis- 

 appearance are mainly three: (1) sterility, or at any 

 rate insufficient fertility; (2) constitutional delicacy; (3) 

 inability to breed true. 



Nor is there any a priori ground for supposing that 

 more ''fit" species arise than ''unfit." 



There have arisen in my cultures besides robust forms 

 like 0. gigas and O. riihrinervis, and weak ones like O. 

 ohlonga and 0. alhida, a series of forms which were 

 either sterile, or were fertile but did not come true to 

 seed. I should have called them transitory species, were 

 it not that all species are transitory. I now refer to the 

 former group as infertile and to the latter as inconstant 

 species. 



Neither of these types can last long in nature. They 

 must obviously be excluded from amongst the species 

 with which the ordinary investigation of nature familiar- 

 izes us. It is only when one can witness a period of 

 mutation that there is any chance of seeing such forms. 



I propose to deal now with some types of inconstant 

 species and shall begin with the one I have investigated 

 most thoroughly. 



This is Oenothera scintillans which is figured on Plate 

 V and in Fig. 47 on page 244. I have already stated, 

 in § 3 of this section, that the seeds of this species pro- 



