NEO-MENDELISM IN PLANTS 419 
It is obvious that the resulting progeny would be one-half white and 
one-half red, although both parents are white. The same result would 
be secured in crossing Nos. 11 and 14. A cross between Nos. 14 and 
15, both of which are heterozygotes, would result in 3 whites and 1 red, 
the ordinary 3:1 ratio. These illustrations show how differently the 
same phenotype may behave in inheritance. In each case two whites 
were crossed, that is, the same phenotypes, but three different ratios 
were obtained because the genotypes were different. 
The striking feature of this situation is that one can cross two 
whites and getared. This gives an insight into the so-called phenome- 
non of reversion. For example, in the course of numerous breeding 
experiments Bateson 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. Fur- 
ther breeding, however, showed that this was just such a case of com- 
plementary factors as we have been considering. 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 defined and the method of their 
inheritance ‘described, but is there any mechanism to explain the 
situation? A suggestion may be obtained from plant chemistry. 
The most prominent group of pigments in plants is the group of antho- 
cyanins, which are produced as follows. Plants contain compounds 
called chromogens, which are colorless themselves but which produce 
pigments when acted upon by certain oxidizing enzymes or oxidases. 
This is a sufficient mechanism for the behavior of complementary 
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 
explainedin connection with East’s corn. This seems to be the explana- 
tion of the behavior of complementary factors in many cases of color 
inheritance. 
Where other characters are involved the mechanism must be some- 
what different. In some cases the two factors may be the enzyme 
