244 A TEXTBOOK OF GENERAL BOTANY 
as C and its absence as ¢, while the other is represented as # 
and its absence as e. | 
Many pigments in plants are produced by the action of 
enzymes on a colorless substance, known as chromogen. What 
may be the explanation of the above case of inheritance in corn 
is that one of the strains of white-grained corn contained a factor 
for chromogen and the other a factor for an enzyme capable 
of acting on the chromogen and producing red. When these 
two strains were crossed, the resulting plants contained both 
chromogen and enzyme, and so the grains were red. 
A consideration of complementary factors shows that more 
than one factor may be necessary to produce a given character, 
and it is probable that any character is the result of several or 
many factors. When the inheritance of a pair of contrasting 
characters appears to be due to a single pair of factors, this does 
not mean that only one factor is necessary for the production of 
a character, but simply that a difference between two factors of a 
pair results in the appearance of a pair of contrasting characters. 
In the case of the inheritance of red color in corn, illustrated in 
Fig. 236, the color is due to at least two factors. However, if 
we were to cross the individuals represented by squares 1 and 6 
in the lower part of the diagram, red would appear to be a simple 
Mendelian dominant, conditioned by a single factor, as the two 
individuals differ from each other only in the factors # and e. 
Not only is one character the result of the interaction of many 
factors, but one factor may influence more than one character. 
Cumulative factors. Some plants contain more than one pair 
of factors which produce similar results. Such factors are 
known as cumulative factors. These may be illustrated by 
certain strains of wheat. In breeding experiments a strain of 
wheat with white kernels was crossed with one with red kernels, 
and the individuals of the #, generation were intermediate in 
color. In the F’, generation there were fifteen red to one white. 
Moreover, the red individuals were represented by four shades 
of red. The explanation of the results is that the red strain 
contained two pairs of factors for the production of red, that 
