488 FUNDAMENTALS OF FRUIT PRODUCTION 



fruits, like the banana, mature their fruits though they bear no mature 

 seeds. This should be emphasized because fruitful plants are often 

 spoken of as being fertile, when, as a matter of fact, they may or may not 

 be. Fertile plants are necessarily fruitful. Self fruitfulness, therefore, 

 refers to the ability of the plant to mature fruit without the aid of pollen 

 from some other flower, plant or variety, as the case may be ; self fertility 

 indicates a similar ability to mature viable seed without the aid of pollen 

 from some other flower, plant or variety. 



Sterility and Unfruitfulness Classified. — In a general way the causes 

 of sterility, unfruitfulness and of the failure of the fruit to set may be 

 grouped in two main classes — those internal to the plant and those ex- 

 ternal, that concern more directly its environment. Frequently it is 

 difficult, if not impossible, to differentiate between these groups of 

 factors, for they are interdependent to an important extent; nevertheless 

 it is convenient to make such a grouping. 



Summary. — The essential organs of the flower as they concern fruit 

 setting and fruit production are the pistils and stamens, though other 

 parts may enter into the structure of the fruit. The changes taking 

 place in the ovule and anther just previous to the time of pollination and 

 fertilization are described in detail. Pollination is followed by the germi- 

 nation of the pollen grain and the growth of the pollen tube, under the 

 influence of chemotropic factors, down the style. With the penetration 

 of the nucellus by the pollen tube and the fusion of one of the generative 

 nuclei of the latter with the egg cell, fertilization is complete, though a 

 secondary fertilization of one of the polar nuclei by the second generative 

 nucleus occurs frequently. The embryo results from the segmentation 

 and growth of the embryo cell and the endosperm is the tissue developing 

 from the polar nuclei. Fertilization is usually followed by a growth of 

 the surrounding ovarian tissues, resulting in a "setting" of the fruit. 

 As a rule only a small percentage of the flowers of most deciduous fruits 

 "set" and many of those that remain fall before the fruit reaches 

 maturity. In many fruits there are several distinct periods of dropping, 

 these distinct waves being referred to as the first, second and June drops. 

 These periods of dropping generally are closely associated with definite 

 stages in the development of the tissues of the ovule. Fruit setting, 

 fruitfulness and fertility are distinguished. The factors responsible for 

 unfruitfulness may be classified for convenience into those which are 

 external and those which are internal to the plant. 



