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 i.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 or as the pollen-parent that is to say, the starchy 

 character is dominant, a dominant character being one 

 which appears in F 1 to the complete or almost com- 

 plete exclusion of the corresponding character ex- 

 hibited by the other parent, which is spoken of as 

 recessive. " In the 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 



