226 MULTIPLE FACTORS 
following case, is the production of a white-seeded 
wheat. A cross between white-seeded and red- 
seeded wheat gave in F, one white to sixty-three reds, 
showing that three independent recessive factors 
were involved. 
Nilsson-Ehle also found that in oats a type without 
ligules reappeared in F, in such a ratio that four 
recessive factors must have combined to have pro- 
duced the type without ligules. East found certain 
kinds of yellow corn that gave in F, fifteen yellows 
to one white. We may here also interpret the white 
as the double recessive. East has pointed out that 
in crosses of certain strains of red corn white appears 
in F, in such a way as to suggest that three or possi- 
bly four recessive factors combine to produce white. 
In other cases of multiple factors, the two factor- 
differences differ in the intensity of their effect, and 
so in F, the two classes aB and Ab can be distin- 
guished from each other, and a 9:3:3:1 ratio there- 
fore results. In some of these cases, however, the 
factors are in a sense non-cumulative in that one of 
the factor-differences produces no effect when a given 
allelomorph of the other pair of factors is present. 
Thus, in the ratio 9AB:3aB:3Ab:lab if, in the 
presence of b, a and A produce no different effect 
there would be a ratio of 9:3:4. This is true ina 
cross of a black mouse (AB) with a white mouse 
carrying both the recessive factor (b) for producing 
an absolutely white color and also the recessive 
(a) which merely “dilutes” the black to blue. The 
“diluter”’ a of course can not have any visible effect 
