MONO-HYBRID CROSSES 183 
formula. It indicates the proportion in which the 
two pure types and their hybrid brethren will appear, 
on breeding together the offspring of a simple or 
mono-hybrid cross—t.e., one in which attention is 
paid to the behaviour of a single pair of characters only, 
So far we have been dealing with a pair of characters 
consisting in the presence and absence respectively of 
a particular pigment. Precisely similar results are to 
be obtained in the case of a pair of structural char- 
acters. The endosperm, or reserve substance, of cer- 
tain varieties of Indian corn shows a smooth surface, 
and contains an essentially starchy reserve material, 
whilst in other races the surface of the endosperm is 
wrinkled and the reserve product is of a sugary nature. 
This sugary endosperm is characteristic of the kinds 
of corn largely used in the United States of America 
as a table vegetable. 
On crossing together a variety with smooth starchy 
grains and one with wrinkled sugary grains, the grains 
immediately resulting are smooth and starchy, no 
matter whether the starchy strain is used as the seed- 
parent oras the pollen-parent—that is to say, thestarchy 
character is dominant, a dominant character being one 
which appears in F, to the complete or almost com- 
plete exclusion of the corresponding character ex- 
hibited by the other parent, which is spoken of as 
recessive. Inthe present case the sugary character is 
recessive. 
The further behaviour of the cross between smooth 
and wrinkled is precisely the same as that of yellow 
