156 



The Principles of Fruit-growing 



keeping in touch with discussions in societies, articles in 

 the rural press, and publications of institutions. . 



6. To a certain extent, one may improve one's varieties 

 by breeding, particularly in the fruits that bear early or 

 young, as the berries, grapes, and even peaches and plums. 

 If one does not care to go to the trouble of raising seedlings 

 of known parentage, one should at least be on the lookout 

 for interesting variations, and should exercise discrimina- 

 tion in the taking of cuttings and cions. 



Self-sterile varieties. 



Choice should be made also with reference to inter- 

 pollination. It is known that some varieties of fruits are 

 self-sterile, that is, they are not fruitful with their own 

 pollen and when planted alone. This 

 sterility may be due, as in the case of 

 the strawberry, to imperfect (or uni- 

 sexual) flowers, or, more commonly, 

 to pollen that is impotent on the pistils 

 of the same flower. This infertility 

 or self-sterility is largely a varietal 

 characteristic, yet it is no doubt 

 modified by seasonal and environ- 

 mental conditions. It is probable that 

 varieties may sometimes be self -fertile 

 and at other times self-sterile. The 



FIG. 25. Strawberry , a _.. _ _ , . , 



flowers modified by strawberry flowers in Fig. 25 show the 

 marked influence on pollen -bearing 

 that is exerted by different conditions. The flowers are 

 of the same variety, and were grown under glass. The 

 lower one shows the small development of stamens in a 

 long cloudy spell, and -the upper one the profusion of 

 stamens that appeared in other flowers after a few 



