394 



POLLINATION AND FRUIT SETTING 



(female gamete), and fertilization is said to have taken place. 

 As soon as fertilization of the egg cell occurs, the embryo, 

 ovary, and other adjoining tissues begin to develop, an increase 

 in size occurs, and the blossom appears to have ^^set." If 

 pollination and fertilization do not occur, the blossoms soon 

 turn yellow, wither, and drop, either at the time the petals fall 



or shortly thereafter. 



Although pollination and 

 fertilization are necessary 

 for fruit setting, this does 

 not mean that all blossoms 

 which are fertilized develop 

 into fruits. Owing to com- 

 petition for water and nu- 

 trients, many of the bios-" 

 soms fall. Some drop at the 

 time of petal fall, some two 

 or three weeks later, and 

 some at the time of the 

 '^June drop/' After fertiliza- 

 tion, those blossoms which 

 have the most seeds and 

 which are borne on the 

 most vigorous spurs, so 

 that more water, nitrates, 

 and elaborated foods are available, are the ones most likely 

 to set. 



2. Self-Fruitful and Self-Unfruitful Tree Fruits. Many 

 varieties of apples, pears, cherries, and plums will not set fruit 

 if the blossoms are pollinated with their own pollen, or with 

 pollen taken from another tree of the same variety. Such 

 varieties are said to be self-unfruitful. If the pollen of such 

 varieties is viable, that is, capable of germination, and the egg 

 cells are normal, the varieties are said to be self -incompatible 

 also. When varieties do set fruit with their own pollen they 

 are said to be self-fruitful and self-compatible. The term self' 

 fertile is used if fruits with viable seeds are produced, following 



{Md, Exp. Sta.) 



Fig. 158. By inclosing trees at blos- 

 soming time under muslin or cheese 

 cloth tents to exclude insects, studies 

 in cross and self-fruitfulness can be 

 made. 



