Neo-Mendelism 55 



ample, in the course of numerous breeding experiments 

 BATESON (i) obtained two strains of white sweet peas, 

 each of which when normally "selfed" bred true to the 

 white color ; but when these two were artificially crossed 

 all the progeny had purple flowers, like the wild Sicilian 

 ancestors of all cultivated varieties of the sweet pea. 

 This appeared to be a typical case of reversion. Further 

 breeding, however, showed that this was just such a 

 case of complementary factors as we have been con- 

 sidering. One of BATESON'S white strains had one of 

 the factors for purple and the other strain had the other 

 factor. 



Complementary factors have been denned and the 

 method of their inheritance described, but is there 

 any mechanism to explain the situation ? A suggestion 

 may be obtained from plant chemistry (2). The most 

 prominent group of pigments in plants is the group of 

 anthocyanins, which are produced as follows. Plants 

 contain compounds called chromogens, which are color- 

 less themselves but wliich produce pigments when acted 

 upon by certain oxidizing enzymes or oxidases. This is 

 a sufficient mechanism for the behavior of comple- 

 mentary factors. If one of EAST'S white strains of corn 

 contained a chromogen capable of producing red but 

 lacked the necessary oxidase it would remain colorless. 

 If the other white strain contained the oxidase but no 

 chromogen it would remain colorless. In crossing them, 

 however, chromogen and oxidase would be brought 

 together and a red-grained hybrid would be the result. 

 Inbreeding such red-grained individuals of course would 

 give red and white progeny in a ratio of 9 : 7, as explained 

 in connection with EAST'S com. This seems to be the 



