122 BOTANICAL GAZETTE [February 



of twin hybrids and one mutation. The soUtary 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 ? 

 gamete, which if pollinated by 0. 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 0. pratincola and numismatica does 

 not yield mut. nummularia, or anything resembling it, with greater 

 frequency than does imhybridized 0. pratincola. Perhaps O. nu- 

 mismatica is itself a mutation from 0. 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. nummularia itself is partially seK-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 poUen 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 0. Lamarckiana. 



2. The most striking of the mutations, 0. 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 fomid in both the 

 Fi and F2 generations from the parent plant. In a third strain 

 the mutation was found only in the F2 generation, but a sufl&cient 

 number of Fi plants had not been grown to insure its detection 

 in that generation. 



4. Mut. nummularia 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. 



