558 



THE AMEBIC AX NATURALIST 



[Vol. XL VII 



Curiously the tendency in this group appeared not to be 

 progressive as to the size of flowers and other plant or- 

 gans, but, instead, retrogressive. There were no plants 

 with flowers larger than those of grandiflora, but in con- 

 trast a large number had flowers (petals 1-1.5 cm. long) 

 much smaller than those of the biennis parent type 

 (petals about 2 cm. long) . The general tendency through- 

 out this group, as well as that of group A, was distinctly 

 downward as regards the size of the plant's organs. 

 This is the first time that I have met with such a phe- 

 nomenon in my observations on second generation hy- 

 brids of Oenothera. 



Considering the culture, as a whole, it presented the 

 same sort of extreme variation that has appeared in 

 other F 2 generations. Many types were present which 

 were taxonomically distinct from either parent of the 

 cross and from the Y 1 hybrid plant 11.35L«. The 

 groups of dwarfs included few individuals, but these were 

 quite as puzzling in their extreme reduction in size as 

 were the dwarf types described from the F t plants 

 10.30L« and 10.30L6. 



4. A Discussion of the Behavior of the Hybrids in the 

 Second and Third Generations with Eeference 

 to the Stability of Mendelian Factors 

 I wish briefly to point out what seem to me difficulties 

 in interpreting the F 2 generations described in this paper 

 in accordance with a strict Mendelian conception of the 

 stability of factors. These difficulties are not presented 

 as a criticism of Mendelism, for the data are not suffi- 

 cient to justify conclusions, but it is well to note the 

 problems. 



As I understand the tenets of strict Mendelism it is 

 assumed that the factors believed to be responsible for 

 characters are stable. New characters are believed to 

 appear either by the loss of factors or by their recombi- 

 nation in the gametes, with possibly the occasional intro- 

 duction of new factors or modification of the old to give 



