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THE AMEBIC AN NATURALIST [Vol. XL VII 



tors or combination of factors that shonld give classes of 

 small-leaved plants to balance the mass of the culture 

 with its progressive advance in leaf size and degree of 

 crinkling. 



I present these problems not altogether as a criticism 

 of the hypothesis of multiple factors which has been so 

 ably applied in the recent CEnothera study of Heribert- 

 Nilsson ('13), and by East, Hays and other investiga- 

 tors in various groups. This hypothesis has amply 

 justified the confidence of its advocates, but it does not 

 seem to me to be established as wholly satisfactory. 

 There has been abundant evidence in my cultures of a 

 segregation of size in the F 2 , but my question is whether 

 this segregation may not be accompanied by a modifica- 

 tion of factors whereby new sets wholly, or in part, take 

 the place of the old. I do not think that East ( 12) quite 

 met the problem in his recent discussion of my data. 



It has been suggested to me that the marked progressive 

 advance in the size of organs in an F 2 generation may 

 result from the continuance of the stimulus of heterozy- 

 gosis (East and Hays, '12) apparent in the F v Is it not, 

 however, possible to view the phenomenon in the F 2 as 

 the direct modification of the factors for size as a result 

 of the cross? One of the most extreme illustrations that 

 I have observed of such an advance is illustrated in Fig. 

 17, which shows rosette leaves of a certain F 2 hybrid 

 plant (12.4124?) in comparison with those of its parents. 

 This plant failed to mature flowers and its study could 

 not be continued. There was certainly indicated very 

 profound changes in its vegetative organization. 



Advocates of the hypothesis of multiple factors for 

 size allelomorphic to their absence may claim the possi- 

 bility of selective fertilization in the formation of zy- 

 gotes preceding an F 2 or later generations. This possi- 

 bility can not be disregarded, but we have no data for the 

 Oenotheras. There has been, however, in my experience 

 usually a high degree of sterility in the seeds of CEno- 



