578 



THE AMERICAN NATURALIST 



[Vol. XLV 



centuries ago which are not known to occur in America 

 to-day. 



The 0. LamarcMana of de Vries's cultures is not the 

 only Oenothera which is no longer known to be wild in 

 this country. The same is true of the " European bi- 

 ennis " so-called, and of a race of 0. biennis having very 

 crinkled leaves, which I have cultivated from the Chelsea 

 Physic Garden. It is not sufficiently kept in mind that 

 the collector or species-maker necessarily abstracts. 

 One form, or at best a very few, arc selected for seeds or 

 for description as types, from a population containing 

 often a large number of closely allied races; for nature 

 does not select between these races unless the differen- 

 tiating characters are of value in the survival of the 

 organism, and this appears often not to be the case. In 

 this manner two or three centuries ago various races of 

 (Enothera were selected and taken to Europe to be 

 propagated in botanical gardens, but it is evident that 

 many more races were left behind, and since the incom- 

 ing of civilization some of these have probably disap- 

 peared. In nature, among open-pollinated (allogamous) 

 plants (and presumably among a great many animals) 

 there is no such thing as a "pure" species which will 

 breed true in all its characters, showing only purely 

 fluctuating variability. It is only by selecting and in- 

 breeding for a few generations, that we get "pure lines." 

 The only pure lines in nature are to be found among 

 strictly self-fertilized (autogamous) forms. This idea, 

 which has been emphasized by Cook ('07), seems to be 

 too frequently lost sight of in evolutionary studies. The 

 pure line, while a valuable and necessary means of 

 analyzing various problems of heredity, is essentially a 

 laboratory product seldom duplicated in nature among 

 allogamous plants. By continued inbreeding and selec- 

 tion to smaller and smaller differences, races which are 



must (unless regularly self-fertilizing) be looked upon 



be obtained, as the "pure 

 lut the natural wild species 



