386 BOTANY OF CROP PLANTS 



Siebold, Mikado, and Japanese Sand are a few of the varieties 

 growniin;the United States. It is also often used to hybrid- 

 ize with ourjcommon pear, the Kieffer variety being the 

 best-known on^ resulting from such a cross. 



Self -sterility in Pears. — The work of Fletcher has pointed 

 out the reasons for the barrenness of many pear orchards. 

 Much of this is due to self-sterility, that is, the inabihty of 

 the pollen of a variety to fertihze the ovules in the pistils of 

 that variety. It has been frequently observed in many 

 portions of the country that when a certain variety of pear, as 

 well as other fruits, was planted thickly, there was often pro- 

 nounced seK-sterility. This is particularly true, it seems, of 

 Bartlett and Kieffer pears. Fletcher obtained the following 

 average results, under Virginia conditions, in self-fertilizing 

 Bartlett, and in crossing with a number of varieties (in the 

 table, the last mentioned variety of a cross furnished the 

 pollen) : 



Pollinations Av. number of Av. weight of 



blossoms set mature fruit, 



ounces 



Bartiett X Bartlett i in 513 2 .00 



Bartlett X Kieflfer i in 10 3.00 



Bartlett X Anjou i in 7 3-75 



Bartlett X Lawrence i in 9 3 . 50 



Bartlett X Duchess i in 10 3 . 50 



The following table shows similar relations in the case of 

 Kieffer pears: 



Pollinations Av. number of 



blossoms set 



Kieffer X Kieffer i in 253 



Kieffer X Bartlett i in 5 



Kieffer X Le Conte i in 7 



Kieffer X Lawrence i in 6 



Kieffer X Duchess i in 5 



Kieffer X Anjou i in 4 



Kieffer X Clairgeau i in 3 



Kieffer X Garber i in 7 



