28 TYPES OF MENDELIAN HEREDITY 
the factor for white both affect the plant in which they 
occur. In this and in similar cases the F, ratio of 
1 :2:1 is obtained, because it is possible to distinguish 
the pure red and the pure white from the heterozygous 
plants. 
Fic. 14.—Diagram to illustrate the cross between a red and a white 
flowered Mirabilis jalapa (4 o’clock), which produces a pink, intermediate 
heterozygote. 
The Andalusian fowl is a similar case. When 
certain races of black are bred to certain races or 
kinds of “white” the hybrid is slate ‘blue”’ in color. 
These blue birds, called Andalusians, when inbred, 
give one black to two blue to one white. Blue is 
