COBN BREEDING 15 
in which the characters merge into one another by more or less 
imperceptible stages. The former was spoken of as alternative in^ 
heritance, the latter as blending inheritance. Now, although the 
names are still used, it is recognized that they are merely different 
forms of the same thing and that there is no clear line of distinction 
between them. Thus, in the inheritance of aleurone color, kernels are 
either colored or colorless. Or, looking at it in another way, they 
range from colorless to dark purple. Aleurone color in corn has 
been chosen for discussion because it is a simple example showing 
the possibilities of multiple-factor inheritance. Careful analysis has 
shown that the inheritance of other characters that intergrade by 
steps so slight as to be almost imperceptible are but more complex 
cases of the same kind, and it now is generally believed that this is 
the way in which many characters are inherited. 
SOME HERITABLE CHARACTERS OF CORN 
The mode of inheritance has been determined for more than 60 
specific factors in corn, many of which are known to affect more than 
a single character. Though it is beyond the scope of this bulletin to 
consider these in detail, some of them may well be described briefly. 3 
It should be pointed out that in describing the method of inherit- 
ance of any given character, only those factors can be considered 
that are known to be operative. In the case of a cross between 
strains having purple and white aleurone, for example, if all of the 
F t kernels are purple and the F 2 segregates into three purple to one 
colorless, it is known that the purple parent differed from the parent 
having colorless kernels by a single factor. That other factor pairs 
were involved could not be recognized until crossing with other ma- 
terial demonstrated the fact. In other words, the genetic relations 
determined in any case represent only the simplest conditions neces- 
sary to account for the observed facts. The evidence is positive for 
the action of certain factors, and the negative evidence that no other 
factors are involved is strengthened as each cross with unrelated 
strains fails to show a more complex condition. Like all negative 
evidence, however, this can be refuted by a single conclusive case to 
the contrary. 
ENDOSPERM COMPOSITION 
The endosperm of corn may be sugary, waxy, or starchy. In the 
sweet or table corns there is a much larger quantity of sugar and a 
smaller proportion of starch than in the field corns, resulting in the 
wrinkled, translucent appearance which they have when dry. The 
composition of the endosperm in waxy varieties differs from that of 
either of the preceding groups. The flint, dent, pop, and flour corns 
all have starchy endosperms, but they differ in the proportions of 
soft and horny endosperm. 
Starchy and sugary kernels differ in a single-factor pair Su su. 
Starchy kernels are either Su Su or Su su, and sugary kernels are 
su su. The factor for waxy, was, is recessive to its allelomorph for 
nonwaxy, Wx. Kernels carrying su su are sugary regardless of 
whether they are Wx or wx. If, therefore, starchy kernels heterozy- 
3 The mode of inheritance of a large number of factors is described in a paper published 
by Lindstrom in 1923 (5k). 
