292 POMOLOGY 



and when insect pollination is the rule, they are called en- 

 tomophilous. 



261. Nature's methods of avoiding self-pollination.^ 



Several means have been developed in nature to prevent 

 self-pollination. Not all of these obtain with fruit-trees 

 but several are very effective. The chief devices among 

 flowering plants are: 



1. Special devices or contrivances of the flower which 

 ensure cross-pollination when insects enter the flower. Or- 

 chids exhibit these adaptations to a greater degree than any 

 other group. 



2. Difference in time of maturity of the stamens and pis- 

 tils. This phenomenon is called dichogamy. When they 

 mature simultaneously, it is homogamy. When the stamens 

 precede the pistils in maturity, it is termed proterandrous, 

 and if the reverse they are said to be proterogynous. 



3. Even though flowers may exhibit homogamy, the 

 relative position of the pistils and stamens or their rela- 

 tive lengths may be such as to prevent self-pollination. 

 Such a condition is termed kerkogamy (dimorphous of 

 Darwin). 



4. Separation of sexes. With most fruits the flowers are 

 perfect, i. e., possess both stamens and pistils, but with some 

 forms this condition does not exist. The strawberry is par- 

 ticularly notorious in this regard, as some varieties possess 

 perfect flowers and others have pistillate flowers only, while 

 others which are perfect have more or less abortive and hence 

 worthless stamens. The grape also exhibits the same set of 

 conditions. That cross-pollination is necessary under such 

 circumstances appears evident. 



262. Effect of cross-pollination on the fruit. — Entirely 

 aside from the results of cross-fertilization on the off- 

 spring, the horticulturist is interested in any effect cross- 

 pollination would have on the somatic tissue of the fruit 



