xi SEX II3 



crossed the double - throwing singles with pure 

 singles belonging to strains in which doubles never 

 occur. The cross was made both ways, and in 

 both cases all the F l plants were single. A distinc- 

 tion, however, appeared when a further generation 

 was raised from the F l plants. All the F plants 

 from the pollen of the double throwing single behaved 



FIG. 27. 



Single and double stocks raised from the same single parent. 



like double throwing singles, but of the F I plants 

 from the ovules of the double throwers some behaved 

 as double throwers, and some as pure singles. We 

 are led to infer, therefore, that the ovules and pollen 

 grains of the double throwers, though both produced 

 by the same plant, differ in their relation to the 

 factor (or factors) for doubleness. Doubleness is 

 apparently carried by all the pollen grains of such 



I 



