CORST BREEDING 17 
and the cross-fertilization that is common under field conditions 
largely prevents their expression. Close inspection of open-fertilized 
corn, however, shows a surprising number of ears with two, three, or 
more defective kernels. An idea of the prevalence of these defectives 
may be had from the fact that among 320 ears of a good strain of 
Boone County corn self -fertilized for the first time, 44 ears (13.75 per 
cent) had heritable defective kernels. 
ENDOSPERM COLOR 
There is at least one specific factor for yellow endosperm color 
(Yy). The color of heterozygous kernels is intermediate in most 
cases. Thus, in general, kernels with Y Y Y are a dark yellow, and 
those with Y Y y and Y y y are successively lighter. Three factors 
are shown in each case, because endosperm color is a kernel character 
in which the female parent contributes two sets of chromosomes and 
the male parent one. A well-known example of this fact is that yel- 
low corn pollinated by white corn tends to be lighter than the pure 
yellow corn, but darker than white corn pollinated by yellow. These 
tendencies, however, sometimes are modified by other factors, so that 
they do not always hold. It seems probable from the several tones of 
yellow in different varieties of corn that other factors for yellow en- 
dosperm also may exist, although these tones may be due to modify- 
ing factors or to differences in kernel structure and the like. A yellow 
or brownish pigmentation of the aleurone cells, determined by the 
factor pair Bn hn (51), also occurs, which gives the kernels an ap- 
pearance of having a pale-yellow endosperm. 
■ 
PERICARP COLOR 
The color and composition of the endosperm and the color of the 
aleurone may show the immediate effect of the pollen parent. The 
color of the pericarp or hull, on the other hand, is determined ex- 
clusively by the female parent in the season in which crossing occurs, 
as the pericarp is formed entirely from the tissue of the female 
parent. Thus, if a variety of corn with a colorless pericarp is 
pollinated by pollen from a variety with a red pericarp there is no 
evidence of this fact when the crossed ears are harvested. When 
planted the next season, however, all of the ears from crossed kernels 
will have red pericarps, and in the next generation three-fourths 
of the ears will have red and one-fourth colorless pericarps. 
Pericarp color is controlled by the factor P, which is dominant 
to its allelomorph p for colorless pericarp; and just as the inter- 
action of J and j gave three green plants to one japonica plant, so 
the interaction of P and p gives three plants with reel ears to one 
having ears with colorless pericarps. There are several allelomorphs 
in the P p series which have to do with variegation of the pericarp, 
cob color, etc. (#,#). Moreover, the factor A, which already has been 
considered in connection with aleurone color, must be present with 
P if the pericarp is to be red. P a gives a brown pericarp instead 
of reel (08). 
Here again the basic facts are simple enough when each is con- 
sidered separately, but become complicated in their interrelations. 
36919°— 27 3 
