266 THE FACTORIAL HYPOTHESIS 
does not assume that any one factor produces a 
particular character directly and by itself, but only 
that a character in one organism may differ from a 
character in another because the sets of factors in the 
two organisms have one difference. This point is 
not likely to be misunderstood by any one who grasps 
the meaning of the factorial hypothesis. The ‘‘or- 
ganism-as-a-whole”’ argument, so long as it is not a 
vague and mystical sentiment incapable of clear 
expression, has no terrors for the factorial hypothesis, 
for this hypothesis disclaims any intention of making 
one unit character the sole product of one factor of 
the germ. 
2. No one disputes that characters vary, but it has 
become necessary to explain what we mean by this 
statement. Many populations have been shown to 
be mixtures of different genetic types. This means 
that many of the individuals have different germ 
plasms. In man, for instance, there are blue-eyed, 
brown-eyed, black-eyed and pink-eyed individuals, 
and these variations of eye color have been shown 
by Hurst, the Davenports, Holmes and others to 
depend on different factorial constitutions. It has 
been shown in several cases, notably in corn, by 
Shull, and by East and Hayes, that populations may 
contain differences in many factors that have 
similar effects on the same character. In this case 
too the different factors that affect a part in the same 
way are shown to separate and recombine in succes- 
sive generations. The result is variability, but 
variability of a sort that is compatible with the 
