16 BULLETIN 1489, U. S. DEPARTMENT OF AGRICULTURE 
gous for both these pairs, Su su Wx wx, are planted and the plants 
are selfed, the following kinds of kernels will be obtained : 
a 1 Su Su Wx Wx "1 e 1 Su Su wx wx \ q 
b 2 Su Su Wx wx L „ fnT , phv f 2 Su su wx wx r waxy * 
c 2 Su su Wx Wx r stdrcny. g 1 m m Wx W(ff 
d 4 Su su Wx wx I 
h 2 su su Wx wx )4: sugary. 
i 1 su su wx wx 
Although groups g and i are indistinguishable in outward appear- 
ance and will breed true, they would give entirely different results 
in the segregating generations following a cross with group a. The 
cross between groups a and g would give a simple Mendelian ratio 
of 3 starchy to 1 sugary, whereas the cross between a and i again 
would give 9 starchy, 3 waxy, and 4 sugary in the F 2 generation (10). 
This is a good example of the way that the presence of a factor or 
character may remain unsuspected for generation after generation 
until an appropriate cross permits its expression. 
ENDOSPERM TEXTURE 
Whether a starchy kernel is a flint or a flour depends upon the 
factor pair Fl fl. This is one of those interesting cases in which 
two doses of a factor coming from the polar nuclei of the female 
are dominant over a single dose of the allelomorph coming from 
the male parent. Thus, a true-breeding flint corn (Fl Fl) shows 
little or no immediate effect if pollinated by a true-breeding flour 
variety (fl fl). Similarly, a flour variety shows no immediate effect 
of pollen from a flint corn. When either of such crosses is self- 
pollinated the kernels segregate into 1 flinty to 1 floury, the condition 
being determined by the two factors from the polar nuclei without 
any appreciable effect from the pollen. Thus kernels having Fl Fl 
Fl or Fl Fl fl in the endosperm are flinty, whereas those with fl fl fl' 
or fl fl Fl are floury. It should be noted that the three doses of the 
factor are present only in the endosperm cells, the embryo being 
Fl Fl, Fl fl, or fl fl, as the case may be (18) . 
The difference between dent and flint and between dent and flour 
corns is more complicated and has not been fully determined. Inden- 
tation probably is due largely to differential shrinkage while drying, 
the soft starch in the center of the kernel shrinking more than the 
horny starch around the sides of the kernel. It is influenced also by 
the shape of the kernels, their closeness on the ear, and other mechan- 
ical effects. Apparently there is a difference in one or more major- 
factor pairs, with further differences in modifying factors, making 
classification difficult. In general, denting is a maternal character. 
That is, the indentation is not immediately affected by the pollen 
parent, and the entire ear has about the same type of indentation. In 
other cases, however, the individual kernels differ, indicating that 
some of the minor factors may produce xenia effects. 
DEFECTIVE KERNELS 
A group of kernel characters closely related in their mode of inheri- 
tance to endosperm composition embraces several different types of 
defective kernels (57). Two types commonly found in corn are 
shown in Plate 5, C and D. These are not found in large numbers 
in open-fertilized corn, as they are recessive to the normal condition 
