CORN BREEDING 11 
alike genetically and endosperm characters may be taken as an index 
of the hereditary composition of the embryo to a certain extent: This 
fact is of much importance in some genetic studies, as it may permit 
classifying* the kernels before planting. Examples of xenia are 
illustrated in Plate 5, in which A shows the effect of partial pollina- 
tion of a colorless strain by a purple strain and B shows the effect of 
^ partial pollination of a colorless sweet strain by pollen from a color- 
less starchy and from a purple starchy strain. 
The statement that the endosperm and the embryo are identical 
must be made with reservations. The endosperm develops from the 
fusion of two polar nuclei with a single sperm nucleus. The female 
parent thus contributes twice as many chromosomes as the male 
parent in endosperm formation, instead of an equal number as in the 
formation of the embryo. In the case of certain endosperm char- 
acters this " double dose " coming from the female is dominant over 
a single dose coming from the male parent. In such cases the ap- 
pearance of the endosperm is determined exclusively by the female 
parent and xenia does not occur. In cases of complete dominance, 
xenia occurs only when the dominant factor is introduced by the male 
parent. The inheritance of endosperm characters has been investi- 
gated intensively and affords some of the best examples of Mendelian 
inheritance in corn. 
MULTIPLE-FACTOR INHERITANCE 
As has been stated, most characters are controlled by two or more 
factor pairs rather than by a single pair as in the case of japonica 
striping. These factors are independent of one another, except for 
linkage, which may be disregarded here to avoid unnecessary compli- 
cation. The principles are the same regardless of the number of 
factors involved. Each pair of factors segregates at the reduction 
division and recombines at fertilization to produce 1 homozygous 
dominant, 1 homozygous recessive, and 2 heterozygous individuals. 
The complexities arise from the interaction of the different factors 
in controlling the characters and from their recombination in a series 
of such 1 to 2 to 1 ratios. 
INHERITANCE OF ALEURONE COLOR IN CORN 
The inheritance of aleurone color in corn may be used to illustrate 
the possibilities of multiple-factor inheritance. The aleurone con- 
sists of a layer of cells surrounding the endosperm just inside of the 
pericarp (fig. 2). It is a part of the endosperm, and its character 
in a cross is controlled immediately by both the male and the female 
parents. The pigment of certain colored types of corn, notably 
those with reddish and purplish kernels, is formed within these cells. 
This color must not be confused with that of corn having red or 
9 reddish pericarps, as in red, strawberry, and bloody-butcher varieties. 
The pericarp is a part of the maternal tissue, as already noted, and 
pericarp characters therefore do not exhibit xenia. 
It has been determined that at least five major factor pairs interact 
to determine the aleurone color of corn ('22). Factors A, C, and R 
are necessary for the formation of red aleurone color, and as they 
are dominant over their respective allelomorphs, a, c, and r, color is 
formed in kernels heterozygous for these factors (A a, G c,R r) as 
