11'2 THEORY OF EVOLUTION 



tion ( back cross ) . This is what is exj)ected if 

 several factor-differences were involved, be- 

 cause the hybrids of the first generation are 

 expected to be more uniform in factorial com- 

 position than are those in the second generation 

 wliicli are produced by recombination of the 

 factors introduced through their grandparents. 

 Excellent illustrations of the same kinds of 

 results have been found in Indian corn. As 

 shown in figure 85 the length of the cob in F^ 

 is intermediate between the parent types while 

 in F:. tlie range is wider and both of the original 

 types are recovered. East states that similar 

 relations have been found for 18 characters 

 in corn. Emerson lias recently furnished 

 further illustrations of the same relations in 

 the length of stalks in beans. 



A similar case is shown by a cross between 

 fantail and common pigeons (fig. 86). The 

 latter have twelve featliers in the tail, while the 

 selected race from which the fantails came had 

 })etween 28 and 38 feathers in the tail. The Fi 

 offspring (forty-one individuals) showed (fig. 

 87) between 12 and 20 tail feathers, M'hile 

 in Fo the numbers varied between 12 and 



