130 

 many times observed this refusal of squashes {Cucurbita 

 maxima to in-breed." 



Pears: Waite,^^* in his well known experiments, has 

 shown that certain varieties of pear are self-impotent. His 

 conclusions are as follows: "The results under those vary- 

 ing; conditions have snbstantiplly agreed, in most cases being 

 remarkably uniform. The fruits resulting from the differnt 

 kinds of pollen showed interesting differences, which tend to 

 corroborate the conclusions." 



"It should also be noted that similar experiments were 

 tried on the apple and the quice along with the pear work. 

 The varieties of apples are more inclined to be sterile to their 

 own pollen than the pears. With the former in the great 

 majority of cases no fruit resulted from self-pollination " 



"(I) Many of the common varieties of pears require 

 cross-pollination, being partially or wholly incapable of 

 setting fruit when limited to their own polJen." 



"(2) Some varieties are capable of self-fertilization." 



"(3) Cross-pollination is not accomplished by applying 

 pollen from another tree of the same grafted variety, but is 

 secured by using pollen from a tree of a distinct horticul- 

 tural variety, i. e., which has grown from a distinct seed. 

 Pollen from another tree of another variety is no better than 

 from the same tree. This failure to fruit is due to the steril- 

 ity of the pollen and not to mechanical causes." 



"(4) The impotency of the pollen is not due to any 

 deficiency of its own, but to the lack of aflBnity between the 

 pollen and the ovules of the same variety." 



"(5) The pollen of two varieties may be absolutely self- 

 sterile and at the same time perfectly cross-fertile." 



13a The pollination of Pear Flowers. U. S. Dept. Agrlc, Div. of Teg. 

 Pathology, BuUetin No. 5, pp. 81-83. 



