CONTROL OF 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 (L), rough and 

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

 having short (S), smooth (Sm), red (R) hair. 

 When such animals are crossed one should get 

 in the F 2 generation 64 genotypes and 8 

 phenotypes, one of each of the latter being 

 homozygous and breeding true, as is shown ya 

 Yig. 54 for trihybrid peas. These 8 pheno- 

 types of this cross are STR, STW ', SSmR, 

 SSrnW, LTR, LTW, LSmR, LSmW. In 

 Figs. 90, C and D, 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 



