XXI.] REMEDY FOR SELF -STERILITY. 355 



never go — are differences in the time of maturity of 

 the two sex -elements and the failure of pollen to im- 

 pregnate its associated pistils. Subsequent steps are 

 the failure of many normal flowers to set fruit, and 

 diminution of the pollen supply. The extensive 

 multiplication or division of impotent or self -sterile 

 individuals, and the setting of the resulting plants in 

 large blocks, have given us unfruitful orchards. If 

 increasing amelioration tends toward a sexual unbal- 

 ance, it must follow that unfruitful orchards are 

 likely to increase unless intelligent mixed planting 

 is brought to the rescue. 



