184 



MULTIPLE FACTORS 



differ in several factors that affect their size. If the 

 parent strains were pure the FI hybrids would all be 

 alike, or rather would show little if any more varia- 

 bility than either parent stock, because all these FI 

 plants receive the same contributions from the 



FIG. 56. At left, a flower of Nicotiana alata grandiflora; at right X. 

 forgetiana; between them are four F 2 flowers, showing the result of 

 segregation both in the length and the spread of the corolla. (After 

 East.) 



parents. But when in the gametogenesis of the FI 

 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 2 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. 



