352 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



Waite ('95) has shown that 22 varieties of pears are self-sterile 

 (unfruitful) and 14 are self-fertile. In many of the "self-fertile" 

 varieties the fruits formed were entirely seedless, while fruits on 

 the same tree resulting from intervarietal pollination were well 

 supplied with sound seeds. In these experiments no essential 

 differences were noted in intervarietal fertility and fruitfulness. 



Lewis and Vincent ('09) report 59 varieties of apple that are 

 self-sterile, 15 varieties that are self- fertile and 13 varieties that are 

 partially self-fertile. The Spitzenberg variety, for example, was 

 found to be feebly self-fertile, giving only about 3 per cent of 

 fruit with self-pollination. While no marked cases of intervarietal 

 sterility were found, there were rather decided differences in the 

 degree of fruitfulness. In many of the " self- fertile " varieties the 

 fruits were seedless. In these varieties, especially, the number of 

 seeds was increased and the quality and size of the fruit were 

 decidedly improved by intervarietal pollination. 



All varieties of the sweet cherry, 16 in number, which were 

 tested by Gardner ('13) were found to be self-sterile under enforced 

 natural self-pollination; 3 per cent was the highest "set" of fruit 

 obtained from any variety. Under field conditions there is 

 evidently greater fruitfulness, although for purposes of fruit- 

 growing the varieties are "practically self-sterile." It was found 

 that at least three varieties are strongly inter-sterile, necessitating 

 the use of other varieties as pollinizers. It is also to be noted 

 that in a few cases reciprocal intervarietal crosses gave different 

 results; crossed one way they were sterile, but crossed the other 

 way they were fertile. The relation of intervarietal sterility to 

 descent is considered by Gardner. It w^as determined that seedling 

 trees in and about orchards of self-sterile varieties are often good 

 pollinizers to these varieties. Also from the knowm pedigrees of 

 several varieties it appears that a seedling variety may be inter- 

 fertile with its seed-parent variety, and that two seedling varieties 

 derived from the same variety may be inter-fertile to some degree. 

 The inter-relationships in respect to sterility are shown to be 

 widely fluctuating and, Gardner concludes, do not show correla- 

 tion with closeness of relationship. While environmental factors 

 are influential in the production of fruit, the marked self-sterility 

 of individual plants, the intra-varietal sterility, and the cases of 

 inter-varietal sterility are not due to "any inherent weakness of 

 cither ovaries or pollen grains" (Gardner '13, p. 17). 



