MULTIPLE FACTORS 231 
differ in several factors that affect their size. If the 
parent strains were pure the F, hybrids would all be 
alike, or rather would show little if any more varia- 
bility than either parent stock, because all these F, 
plants receive the same contributions from the 
Fie. 56.—At left, a flower of Nicotiana alata grandiflora; at right N. 
forgetiana; between them are four F, flowers, showing the result of 
re both in the length and the spread of the corolla. (After 
parents. But when in the gametogenesis of the F, 
plants these factors segregate, many new combina- 
tions will be formed, and among them will be a few 
combinations like those in the original varieties; 
hence we expect in the F, a wider variability, with a 
return to the grandparental types in a certain per- 
centage of the plants. East suggests that four 
pairs of factors may cover the results in this instance. 
