224 



BREEDING CROP PLANTS 



1. The heterozygous condition of most varieties. 



2. The difficulties of obtaining crossed seed. 



The heterozygous condition need not be further emphasized. 

 Conditions are much the same as in the fruit crops. 



The Difficulties of Obtaining Crossed Seed. The technic 

 of making a cross is very simple. According to East (1908a), 

 "The flowers close slightly about dusk and open in the morning 

 between five and six o'clock. The pollen appears to be in the best 

 condition for use on the second day of blooming." Stuart (1915) 

 collects flowers to be used as the male parent in small sacks. 

 After the pistil is removed from these flowers the anthers are 

 tapped sharply with a pair of forceps, the pollen is collected 



FIG. 54. Emasculated and unemasculated potato blossoms. (After Stuart.) 



on the thumb nail and then applied to the pistil of the emascu- 

 lated flower. The flowers are receptive two to four days after 

 emasculation. East ( 1908a) stated the belief that the potato is 

 usually self-fertilized. He also observed the fact that insects were 

 seldom seen to visit the flower. Salaman (1910-11) believes 

 it unnecessary to cover the flower before or after pollination. 

 Stuart, however, used 1-lb. bags and found that if a certain 

 amount of foliage was included in the bag the use of bags did 

 not cause a lowering of the number of seeds set. An average of 

 between one and two hundred seeds was obtained from each suc- 

 cessful cross by Stuart. 



The chief difficulty is that many varieties do not bloom very 



