22 



BREEDING CROP PLANTS 



which are not present in either parent, appear. These may 

 result from the interaction of two or more factors all of which 

 are necessary for the production of the character and part 

 of which were contained in one parent and part in the other 

 parent. These facts may be illustrated by the results of certain 

 crosses. 



A Cross in Which the Parents Differ by a Single Factor. 

 Sweet corn when mature bears wrinkled seed while flint corn 

 produces smooth seeds filled with starch grains. If sweet corn 



FIG. 6. Inheritance of starchy and sweet endosperm in maize. A, Ear 

 of sweet corn with wrinkled seeds; C, ear of flint corn with starchy seeds; B, 

 immediate result of pollinating ear of starchy parent with pollen from sweet 

 parent; D, produced by self-fertilizing an ear of an Fi plant of cross between 

 sweet and starchy parent. Note the segregation into sweet and starchy seeds; 

 E. An ear produced by planting wrinkled seeds of D; F, G, H, ears produced by 

 planting starchy seeds of D. Note that one out of every three ears is pure for 

 the starchy character. (After Babcock and Clausen.) 



is pollinated with pollen from a flint variety the resultant seed 

 is starchy. There is an immediate effect due to double fertili- 

 zation in which the endosperm results from the union of the 

 polar nuclei with one of the gametes of the pollen grain. If the 

 crossed seeds are planted and the resultant plants self-fertilized, 

 the ears produced will contain starchy and sweet seeds in a 3 : 1 

 ratio. The facts may be presented by the use of the factor 

 hypothesis. One of the chromosome pairs contains the factors 

 for either the starchy or the sweet condition. Let S represent 

 the sweet factor, F the starchy factor. In the following diagram 

 only one of the chromosome pairs, which contains the starchy 

 and sweet factors, will be shown. 



