OENOTHERA LAMARCKIANA MUT. VELUTINA. 



(with plate 1) 



One of the rarest mutations of Oenothera Lamarckiana is that in 

 which those qualities are changed which constitute the characters 

 of the twin hybrids laeta and velutina 1 ). This is the more striking 

 because in hybrid combinations these twins appear often and, as 

 it seems, easily. But in the same way many other mutations, which 

 apparently might reasonably be expected, have not as yet been 

 observed and therefore must be assumed to be at least very rare. 

 Why some mutations are common and others rare is still an open 

 question. 



From the behavior of the twin hybrids in crosses we may deduce 

 that the mutant velutina must be in the main recessive to the parent 

 species, and that the mutant laeta should be dominant over the 

 velutina. If there were but one character involved, this would mean 

 that the mutant laeta must be externally like 0. Lamarckiana, 

 and the same conclusion would have to be admitted if there were 

 more characters indissolubly bound together. This being granted, 

 the laeta could, of course, never be expected to appear as a mutant. 



For some years, however, my cultures tend to show that the 

 mutations observed in the group of the Oenotheras are far more 

 compound phenomena than I was formerly inclined to assume. 

 This also seems to be the case with the splittings which so often 

 occur after hybridization, and especially with those which appear 

 in the first hybrid generation. If we apply this view to the twin 

 hybrids laeta and velutina, the possibility is at once revealed that 

 the components of this group of characters might not always be 

 so indissolubly connected, and that some deviating combination 

 of these qualities might still produce a mutant laeta, different from 

 the type of Lamarckiana. As a matter of fact, a pure and complete 

 mutant velutina has appeared in my cultures, but a laeta has never 

 been seen as a mutant. In crossing this velutina with the parent 

 species, however, twin hybrids arose, one of which may be designated 

 as laeta, as will be shown later. 



!) On twin hybrids. Bot. Gaz. 44 : 401-407. 1907. Opera VI, p. 472. 



