CONTROL OP HEREDITY: EUGENICS 381 



acters have been made repeatedly, and with 

 almost the same certainty of results as when 

 the chemist makes combinations of elements 

 or radicals. 



In Fig. 90, A and B, are shown two 

 guinea-pigs, one having long (i), rough and 

 tumbled (T), white {W) hair, and the other 

 having short (xS"), smooth (/S'm),red {B) hair. 

 When such animals are crossed one should get 

 in the F2 generation 64 genotypes and 8 

 phenotypes, one of each of the latter being 

 homozygous and breeding true, as is shown in 

 Fig. 54 for trihybrid peas. These 8 pheno- 

 types of this cross are STB, STW, SSmB, 

 SSmW, LTB, LTW, LSmB, LSmW. In 

 Figs. 90, C and B, and 91, A, B, C, are 

 shown 5 of these 8 phenotypes which were ob- 

 tained by Castle from this cross. These fig- 

 ures well illustrate the new combinations of 

 Mendelian characters which may be obtained 

 by cross breeding. 



This is the chief method employed by Bur- 

 bank in producing his really wonderful "new 

 creations in plant life." By extensive hybridi- 

 zation he brings about many new combinations 



