CORN BREEDING 21 
really simple. Generally it is exceedingly complex in itself and is 
further complicated by the variation in expression resulting from an 
ever-changing environment. 
INHERITANCE OF PRODUCTIVENESS IN CORN 
The production of grain is the final expression of all of the inherent 
characters of size and function, as limited by the environment in 
which the plants are grown. The inheritance of productiveness, 
therefore, must mean the inheritance of all the characters of size and 
function, which probably includes most if not all of the heritable 
characters of corn. It is a convenience in considering the inheritance 
of productiveness to group the characters affecting it into abnor- 
malities, specific adaptations, and size characters. It should be kept 
in mind, however, that this classification is entirely arbitrary, made 
for convenience, and that, in general, any specific character might be 
placed in one group or another, depending upon the point of view. 
ABNORMALITIES 
Such characters as albinism and other chlorophyll deficiencies, 
dwarfness, heritable barrenness, and the like may be included under 
abnormalities. These characters are sufficiently striking to be de- 
tected readily, and their mode of inheritance can be determined in 
more or less detail. A number of these have been considered in 
preceding pages, and their importance in determining productiveness 
is evident. Thus, regardless of how excellent the rest of the genetic 
complex may be, a corn plant can produce nothing if it is barren 
or if it is genetically an albino and so can not live after the nutri- 
ment in the seed is exhausted. Similarly, a partial lack of chlor- 
ophyll may reduce its productiveness to a point proportional to this 
lack. Again, a dwarf plant attaining a height of perhaps 18 inches, 
with other parts proportionately small, can not equal the production 
of a normal plant of 8 or 10 feet; and this, too, regardless of the ex- 
cellence of the rest of its heritage. 
SPECIFIC ADAPTATIONS 
Such characters as resistance to various disease organisms and to 
unfavorable conditions of soil and climate may be considered as 
characters of specific adaptation. The mode of inheritance of such 
characters is essentially the same as that of the preceding group. In 
fact, they differ from the so-called abnormalities chiefly in the point 
of view involved and in the necessity of specific conditions for their 
full expression. Thus, extreme susceptibility to corn smut, in con- 
nection with the presence of smut and conditions favorable to its 
development, may produce plants that are quite as abnormal as 
dwarfs. Similarly, susceptibility to one of the root rots under con- 
ditions favorable to the root rot may result in the death of the seed- 
ling just as certainly as will albinism under any conditions. 
The inheritance of a number of such characters in other plants 
has been shown to be just as definitely Mendelian as, for example, 
aleurone color in corn. Because of complexities due to cross-fertili- 
zation in corn, detailed information is not so abundant regarding 
