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freely, although the general belief is that all varieties may bloom 

 under certain conditions of environment. East (1908a) classified 

 varieties as follows: 



"1. Varieties whose buds drop off without opening. 



"2. Varieties in which a few flowers open, but which immediately 

 faU. 



"3. Varieties whose flowers persist several days, but which rarely 

 produce viable pollen. 



"4. Varieties which under most conditions always produce viable 

 pollen." 



In 487 out of 721 varieties under observation the buds fell off 

 before the flowers opened. Stuart, however, obtained a much 

 higher percentage of varieties which produced flowers in which 

 the blossoms opened before the buds fell. These results are 

 given to emphasize the fact that conditions widely influence 

 seed production. 



The lack of fertile or healthy pollen in many varieties prohibits 

 their use as parents. The relation between the percentage 

 of healthy pollen and fruit production was determined by East 

 (1908a) for a considerable number of crosses (see Table LIV). 



TABLE LIV. RELATION BETWEEN PERCENTAGE OF VIABLE POLLEN AND 

 FRUIT PRODUCTION 



Somewhat similar results were obtained showing a positive 

 correlation between fruit production and the percentage of multi- 

 nucleate pollen grains. Such grains may be determined under 

 the microscope by their slight protuberances. Germination tests 

 in seven per cent, sugar solution showed that a pollen tube grew 

 from each protuberance in a multinucleate grain. These results 

 obtained by East have been corroborated by the studies of 

 Stuart. In some cases, however, seed production is not difficult 

 to obtain as the data from Stuart show (Table LV). 



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