THE FLOWER 49 



fore, to have mutual affinity, but of these ''affinities" there is 

 yet much to be learned. In studying flowers of the different 

 fruits the student will find two types that tend to bring about 

 self-sterility. In one type the pollen is discharged from the 

 anthers before the stigmas are ready to receive it ; such flowers 

 are said to be protandrons ; flowers in which the stigmas are 

 mature to receive the pollen before the anthers are ready to 

 discharge are said to be protogynous. Flowers of the apple and 

 pear are usually protogynous. 



79. Effects of cross-pollination on the fruits. — It is a common 

 belief among fruit-growers that when pollen from one variety 

 fertilizes the ovules of another, the characteristics of the pollen 

 parent are impressed on the resulting fruit. Many experiments 

 have proved that fruits are not changed in any of their char- 

 acters by foreign pollen, except, possibly, in size which may be 

 increased through pollen stimulation. A better set of crop and 

 greater uniformity in the fruits may also be a result of foreign 

 pollen, especially when there is an excess. 



80. Fruit development without fertilization. — Some varieties 

 of all hardy fruits are seedless and occasionally individuals are 

 found without seeds. In these cases fruits have developed with- 

 out fertilization; this phenomenon is called parthenocarpy. In 

 cases very exceptional, if indeed they occur at all in fruits, the 

 ovule may produce a new plant without having previously 

 united with a male cell, a condition known as parthenogenesis. 

 While parthenocarpy is not uncommon in any hardy fruit, cases 

 most often occur in the pomes and in grapes. As a rule, how- 

 ever, lack of fertilization is followed by the falling of blos- 

 soms, and if all of the ovules are not fertilized by unsymmetrical 

 fruits. 



81. Cross-fertilization between varieties, species, and genera. 

 — Varieties of the same species readily cross-fertilize; the re- 

 sulting progeny are called cross-breeds, variety-hybrids, or the 

 plant may be spoken of as cross-bred. Cross-fertilization may 

 take place between different species of any of the hardy fruits, 

 as black and red raspberries, plum and apricot, sweet and sour 

 cherries. Cross-fertilization between species is called hybridiza- 

 tion and the resulting plants are hybrids. When the species are 

 of the same genus, the progeny may be designated as species- 



