122 BOTANICAL GAZETTE [FEBRUARY 
of twin hybrids and one mutation. The solitary exception 
was broader leaved than the rest of the culture and is inter- 
preted by the writer as the product of a cross between a mutated 2 
gamete, which if pollinated by O. pratincola would have yielded 
mut. nummularia, and a normal ¢ gamete of O. numismatica. 
This hypothesis will be tested later by appropriate crosses. It is 
clear that a cross between O. pratincola and O numismatica does 
not yield mut. nummularia, or anything resembling it, with greater 
frequency than does unhybridized O. pratincola. Perhaps O. nu- 
mismatica is itself a mutation from O. pratincola, or a form which 
has segregated from the cross mut. nummularia X O. pratincola. 
One would expect the latter cross to occur rather often if, as seems 
to be the case, mut. mummularia itself is partially self-sterile. It 
seems not unlikely that in nature self-sterile or nearly self-sterile 
mutations may be perpetuated by effective cross-pollination, either 
as stable hybrids or as homozygous forms resulting from subse- 
quent segregation. It is an interesting fact that although O. 
pratincola has a very high proportion of good pollen grains (90 
per cent or more), mut. nummularia rarely has pollen which is 
50 per cent perfect, and some anthers produce no good pollen 
at all. 
Conclusions 
1. Oenothera pratincola, a recently described small-flowered self- 
pollinating species from Kentucky, is in a mutating condition com- 
parable with that of O. Lamarckiana. 
2. The most striking of the mutations, O. pratincola mut. 
nummularia, occurred in strains derived from 7 wild mother plants 
out of 8 selected at random. 
3. In two of these strains the mutation was found in both the 
F, and F, generations from the parent plant. In a third strain 
the mutation was found only in the F, generation, but a sufficient 
number of F, plants had not been grown to insure its detection 
in that generation. 
4. Mut. xummularia appears to occur with a frequency of about 
one individual to each 300-400 seeds planted. The several proge- 
nies showed no significant variation in the mutation ratio. 
