No. frfS ] 



MUTATION IN (ENOTHERA 



5T9 



as an intercrossing population of races, whose appear 

 anee is ever changing (within limits) from generation 

 to generation, according to the particular series of en>s>e- 

 or selfings which happen to occur in each generation. 

 Some of the races are likely to fluctuate in numbers or 

 be dropped out entirely as conditions change. The way 

 in which the face of the population changes from one 

 generation to another will, of course, depend upon how 

 the character-differences are inherited, hut we need not 

 consider that question here. 



It therefore seems to be idle to inquire whether in 

 this sense crossing of the allogamous Oenotheras, such 

 as 0. Lamarckiana and 0. grandifiora, has taken place, 

 for we must assume that it has occurred, in the wild 

 condition as well as in gardens. Our " species" (par- 

 ticularly the earlier ones, when less fine distinctions 

 were drawn than now) are founded upon certain chance 

 combinations resulting from such crosses, which have 

 attracted attention and been abstracted and rendered 

 uniform by continued self-pollination. Nature herself 

 is oblivious of the boundaries between "species" so 

 long as, when crosses occur, the progeny are fertile, and 

 this is frequently the case in (Enothera. 



I am greatly indebted to Dr. B. Dayton Jackson, gen- 

 eral secretary of the Linmean Society, for the privilege 

 of examining the type specimens of Linnaeus '& "Species 

 Plantarum," and to Dr. A. B. Rendle and his colleagues 

 of the British Museum (Natural History) for courtesies 

 in connection with the examination of extensive (Eno- 

 thera collections, including the plants of Linnaeus 's 

 "Hortus Cliffortianus" and various early American 

 collections. 



The species of (Enothera which need particularly to 

 be accounted for are what we now know as 0. muricata 

 L., 0. biennis L., 0. Lamarckiana Ser. and 0. grandi- 

 flora Ait. Each of these "species" is really an aggre- 



nany 



