CONTROL OF HEREDITY: EUGENICS 393 



types of this cross are STR, STW, SSmR, 

 SSmW, LTR, LTW, LSmR, LSmW. In 

 Figs. 90, C and £>, 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 

 of old characters, a few of which may be com- 

 mercially valuable, and sometimes actually 

 new characters or mutations appear, possibly 

 as a result of the interaction of old characters, 

 or rather of their factors. Lotsy, for example, 

 maintains that the sole source of variation is 

 crossing, and Bateson says that the new breeds 

 of domestic animals made in recent times are 

 the carefully selected products of recombina- 

 tions of pre-existing breeds, and that most of 

 the new varieties of cultivated plants are the 

 outcome of deliberate crossing. 



