708 
GENETICS: B. M. DAVIS 
which produce the twin hybrids and that homozygous combinations of 
gametes axe represented in the sterile seeds. Occasional fertile com- 
binations of gametes varying from the usual type may then be respon- 
sible for the so-called mutants which owe their peculiarities to segrega- 
tion phenomena, to be expected in a hybrid, rather than to spontaneous 
modifications such as are assumed by the mutation theory. 
Finally, in this brief criticism of Oenothera Lamarckiana as repre- 
sentative of a pure species and therefore suitable material for conclu- 
sions on the importance and character of mutations in organic evolution 
it should be pointed out that there is no evidence that this plant is a 
wild species native to the American continent which was the original 
habitat of the group. On the contrary we have reason to believe that 
Lamarckiana was brought into cultivation from material growing in 
England where the early introduction of Oenotheras established some 
extensive colonies probably of mixed and hy^Dridized character. It has 
also been found possible by crossing two carefully selected species of 
Oenothera (franciscana X biennis) to synthesize a hybrid scarcely to be 
distinguished in its systematic characters from Lamarckiana and this 
product which has been named neo-Lamarckiana forms twin hybrids 
when crossed with certain species that give twin hybrids with Lamarck- 
iana. Neo-Lamarckiana when selfed throws a much larger progeny 
of variants than does Lamarckiana but this fact seems to be correlated 
with its much higher seed fertility, from 84 to 87 %. These variants 
have been repeated in their essential characteristics through three gen- 
erations and the parallel of this behavior to that of Lamarckiana is 
very close although as would be expected, the types of variants are not 
the same. Thiis an undoubted hybrid among the Oenotheras has been 
shown to present breeding habits similar to those of Lamarckiana. 
The behavior of neo-Lamarckiana when selfed appears most readily 
explained as due to the breaking up of a hybrid rather than by prin- 
ciples of mutation since characters more or less similar to those of the 
parents appear among the derivatives. 
In addition to the studies on Oenothera Lamarckiana and its 'mutants' 
there has been a very large amount of work by De Vries, Gates and 
others involving other species of Oenothera and more recently exten- 
sive studies by ShuU, Bartlett and Atkinson. These have brought out 
some very puzzling situations in the behavior of Oenothera species in 
crosses. In some cases the first generation hybrids show pronounced 
resemblance to the paternal parent of the cross, in other cases to the 
maternal parent, and still other combinations give blends with inter- 
