552 HEREDITY 
for a part of the character, that, although they do segregate and 
combine according to Mendelism, they form so many kinds of 
combinations and thus so many kinds of individuals occur in the 
second generation of hybrids that it is difficult to detect Mende- 
lian ratios. For example, in the case of crossing the tall and small 
varieties of Corn, it is assumed that the tall variety has a number 
Fic. 481.— Inheritance of size and beards in Wheat. Parent types 
(Turkey X Bluestem at the left and a hybrid No. 143 at the right) and be- 
tween the parent types the F; generation of the Cross. In the F; generation 
the heads are somewhat intermediate in size and have short beards. After 
Gaines. 
of factors for size that are not present in the small variety. Let 
us suppose the large variety has four extra factors for size that 
are not present in the small variety. These factors may be rep- 
resented by A, B, C, and D. Since the tall variety is pure for 
its height, its extra height over the small variety is due to the 
presence of AABBCCDD, and the corresponding constitution of 
the small variety is aabbccdd, in which the small letters represent 
