Reproduction 



363 



established an important principle in fruit-growing when 

 he showed that many varieties of the pear are self-sterile. 

 In the case of some varieties the capacity to set fruit when 

 self-pollinated is wholly lacking ; in other cases when the 

 varieties are limited to their own pollen, normal fruits 

 may be developed, yet even then fruit production is con- 



FIG. 103. Difference in size of pears self (a) and cross pollinated (6). 



[After Waite.] 



sidered to be less certain and the size often slightly re- 

 duced. These results, and many others since reported by 

 various observers, are particularly interesting, since self- 

 pollination has reference not merely to the use of pollen 

 from the same plant, but also from other individuals within 

 the variety. We are dealing, in this case, with clonal 

 varieties, such varieties being maintained by budding and 

 grafting. Different individuals are looked upon, therefore, 

 as very closely related. In most instances all are de- 



