44 AN ANALYSIS OF THE EFFECT OF SELECTION. 
flowers of the deep purple Black Prince were among the earliest varia- 
tions to appear, while the intermediate forms have arisen later, as he 
suggests by fractionation. It would seem to follow that they have 
arisen in heterozygous forms, for otherwise the fact that the larger 
variants appeared first would be of no significance. There is, I think, 
no evidence to show that the later variations did actually arise in 
heterozygous forms, either in sweet peas or in rabbits. These factors 
are all inherited separately, and this fact would seem to rule them 
out of consideration if one adopts the chromosome theory of inheritance 
or if one appeals to multiple allelomorphs as evidence in favor of the 
variability of genes. In short, we have no evidence regarding the 
origin of these forms, and their present behavior seems to indicate 
that they are not due to fractionation. The only evidence in favor 
of such a hypothesis is the somatic appearance of the characters. 
10. FLowERING TIME IN P2ras. 
Castle (1916a, p. 324) has summarized this case as follows: 
“Hoshino (1) recognizes that gametic contamination results from cross- 
ing early and late flowering varieties; (2) recognizes also that variation may 
occur among the cross-bred families, as well as in different pure lines of the 
uncrossed races, as regards the ‘quality,’ value, or potency of the same gene; 
(3) although Hoshino does not refer to the fact, his observations show clearly 
that genetic variation of a gradual or fluctuating sort occurs in at least one 
of the varieties which he crossed. 
; What I want to suggest is that in these several agencies we 
have a sufficient explanation of the variation observed in Hoshino’s Fe, Fs, 
and F, generations, without invoking a two-factor hypothesis (as Hoshino 
has done), one factor being enough.” 
Castle’s argument is that a difference in one pair of genes is sufficient 
to account for the result, if contamination be assumed; and that one 
difference is a simpler assumption than two. I have argued here that 
such an assumption is not simpler, unless we can find positive evidence 
that contamination ever occurs. In the present case, then, we must 
turn to the evidence that led Hoshino to suppose contamination to 
have occurred. 
Hoshino crossed an early-flowering pea and a late-flowering one. 
The F, was nearly as late as the late parent; F:, obtained by self- 
fertilizing F,, approximated fairly closely to 3 late :1 early, but the 
two classes were somewhat more variable than the corresponding 
parent varieties, and apparently overlapped slightly. Hoshino self- 
fertilized 236 of these F, plants and obtained 46 families that he 
classified as constant, 7. e., supposedly homozygous. This is a fair 
approximation to the 1 in 4 expected if two pairs of genes are respon- 
sible for the result. Hoshino shows that two pairs of genes will, in fact, 
account for most of the results obtained. There are certain facts not 
thus accounted for, but Hoshino shows (p. 265) that “‘secondary”’ 
