330 THE AMERICAN NATURALIST [Vol.L 



earlier, and considers this to be evidence of dominance, 

 but I am inclined to think it should be interpreted differ- 

 ently, for F 2 plants having the genetic properties of F 5 

 plants are in some cases at least (Hoshino's Tables T and 

 V) much earlier in flowering time, being in fact almost 

 exactly intermediate between the parent races, although in 

 one family (S) the F 2 plant was late like F x , but its F 3 and 

 F 4 descendants covered the entire range, as did those of 

 T and U. I am inclined to interpret the inheritance as 

 truly intermediate and to explain the lateness of F } and 

 of an occasional F 2 individual as due to physiological non- 

 genetic causes. Eecent observations made on size in- 

 heritance in guinea-pigs together with certain observa- 

 tions recorded by Hoshino lead me to this conclusion. 

 When the small Cavia cutleri is crossed with the rela- 

 tively large guinea-pig, the F 1 hybrids are larger than 

 either parent, but the F 2 hybrids as a group are close to 

 intermediate and only a little more variable than F x . A 

 stimulus due to crossing makes Fj larger than its genetic 

 constitution would otherwise make it, but the added size 

 due to this stimulus does not persist to any great extent 

 beyond F,. Hoshino's Fj peas probably possess a simi- 

 lar vigor due to crossing, which quickly disappears in 

 later inbred generations. If this vigor due to hybridiza- 

 tions causes extra growth it may delay flowering time, 

 for Hoshino, confirming Keeble and Pellew, has shown 

 that late-flowering plants have longer internodes than 

 early-flowering ones. 



Hoshino, as we have noted, divides his F 2 families 

 into two portions, early-flowering (chiefly white) and 

 late-flowering (chiefly red). But we have seen reason 

 to think that the F 4 families fall naturally into three 

 portions, early, medium and late, and it is possible 

 to divide the F 2 families in a similar way, though of 

 course somewhat arbitrarily, classing as early those fall- 

 ing within the range of the early parent or a little beyond 

 it, and as late those which fall within the range of the 

 late parent, while those which lie between a^re placed in 



