No. 538] MUTATION IN OENOTHERA 



to the contrary merely distorts the facts. If it be as- 

 sumed that 0. Lamarckiana is the sudden product of a 

 single cross between two rather more widely separated 

 species, the situation is slightly though not fundamen- 

 tally changed. As regards 0. Lamarckiana, the only 

 forms we know which could reasonably he supposed to 

 be its ancestors in this way would be 0. biennis and 0. 

 grandiflora, as I have already pointed out (Gates, '11a, 

 ]). 119). There have doubtless been plenty of opportuni- 

 ties for these species to cross in Botanical Gardens and 

 they have doubtless done so, since the evidence seems 

 clear that certain races belonging to these two "species" 

 were recognized as early as 1686 by Kay as under culti- 

 vation. 4 But these species both came from the Virginian 

 region, where there is ample evidence that 0. grandi 

 flora as well as 0. biennis originally grew wild, and 

 where the former species was commonly found as late 

 as 1820 (Barton's "Flora of North America," plate 6). 

 Under these circumstances there must have been plenty 

 of opportunities for 0. grandi flora to be pollinated from 

 0. biennis (these forms are visited by moths in the even- 

 ing when the flowers open), and it would be a bold as- 

 sumption to suppose that such crosses had not taken 

 place centuries before the white man came to America. 

 Hence if this were the manner of origin of 0. Lamarcki- 

 ana, it must have originated in nature long ago. Of 

 course it is well-known that many such species-hybrids are 

 sterile so that when they occur they fail to bridge the 

 gap between species or to take any part in those species' 

 subsequent history and evolution. Assuming that 0. 

 Lamarckiana originated in this way, its fertility makes 

 its presence in the population of forms of equal im- 



