418 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
The situation is thus explained by the dihybrid ratio, but although 
only one character is involved that character depends upon two com- 
plementary factors. 
Another situation is worth noting. No. 6 of the diagram is white 
because it contains only one of the necessary factors; No. 11 is white 
56 
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Fic. 79.—Diagram illustrating behavior of complementary factors in cross 
between red-grained and white-grained corn. R and C must both be present to 
produce red-grained corn. (From Coulter and Coulter.) 
for the same reason, but its germinal constitution is just the opposite. 
What would happen if these two are crossed? There is only one 
possibility, since each is a homozygote producing only one kind of 
gamete. The result would be red, and thus a cross between two whites 
would produce only reds. What would happen from crossing Nos. 6 
and 15, the former being a homozygote and the latter a heterozygote ? 
