No. 561] GENETIC AL STUDIES ON OENOTHERA 



5C1 



tain characters appears to advance as a whole presents 

 the second problem to be considered. This phenomenon 

 was also best exhibited by the F 2 generations from the 

 hybrids 10.30La and 10.30L6. A large number of plants 

 in these cultures bore flowers with petals 1 cm. longer 

 than those of the grandiflora parent (petals about 3.3 cm. 

 long), and the smallest flowers were, for the most part, 

 two or more times larger than those of the biennis pa- 

 rent (petals about 1.3 cm. long) ; between these ex- 

 tremes was a very perfect range of intermediates. An 

 explanation for the advance in flower size over that of 

 grandiflora may, of course, be offered as a recombina- 

 tion of factors for large size on the hypothesis of mul- 

 tiple factors for the size of petals, but why was there not 

 a balancing group of plants with flowers as small as or 

 smaller than those of biennis? Even the dwarfs of these 

 cultures had flowers larger than those of the biennis pa- 

 rent. The only plant having smaller petals was the ex- 

 traordinary form 11.42 j (Fig. 15). What had become 

 in these cultures of the factors responsible for small 

 size? 



A similar situation was presented by the character of 

 the foliage most markedly exhibited by the F 2 genera- 

 tions from 10.30La and 11.35a. The leaves throughout 

 the mass of these cultures were much larger than those 

 of the parents of the cross and much more crinkled. 

 There was thus a marked progressive advance in leaf 

 size with the absence of small-leaved classes of plants 

 unless such were represented in the F 2 from 10.30La by 

 the dwarfs. Admitting that possibility, the same prob- 

 lem must be faced as was discussed for the explanation of 

 the dwarfs themselves which were present in a ratio of 

 about 1 : 9, suggesting the 1 : 15 ratio with the presence of 

 two factors for leaf size. Thus two factors for leaf size 

 should give through the culture other classes besides 

 those of the recessives, and these were not evident. Ap- 

 plying the hypothesis of multiple factors for leaf size 

 one is compelled to enquire what has become of the fac- 



