492 FUNDAMENTALS OF FRUIT PRODUCTION 



flowers on trees of the caprifig class — pistillate, staminate and gall. The gall 

 flower is regarded as a specialized pistillate that can harbor the pollen-carrying 

 Blastophaga wasp but cannot develop seed. Rixford,"^ on the other hand, holds 

 that all so-called gall flowers are in reality simple pistillates, not structurally 

 different from other pistillate caprifig flowers that occasionally are pollenized, 

 set fruit and form seed. Usually they do not have the opportunity to set 

 and develop seed because they are not pollinated or because they are stung by 

 the Blastophaga and subsequently become galls. 



Eisen^o and many others recognize a third kind of pistillate flower which 

 they call ''mule" flowers. These are produced by most of those cultivated 

 varieties which yield seedless fruits. They are held to be somewhat different 

 in structure from the pistillates of such varieties as the Smyrna, that are capable 

 of setting seed. However, Rixford"^ has shown that these so-called mule 

 flowers do set and mature seed when properly pollinated and consequently 

 considers them true pistillates. 



Heterostyly. — It has been stated that the flowers of many species present 

 peculiarities of form and structure, the main function of wliich is to aid in bringing 

 together the male and female gametes so that fertilization may take place and 

 reproduction be insured. However, many of these peculiarities of form and 

 structure are of such a nature as to prevent self pollination and make cross 

 pollination more certain. If cross pollination does »ot occur, the plant is very 

 likely to remain unfruitful even though perfect sex organs have been developed. 



One of these diversities of form is heterostyly, a type of dimorphism in which 

 some of the flowers have short styles and long filaments and other flowers of the 

 same species or variety have long styles and short filaments. The structure 

 and arrangement is such that when these flowers are visited by pollen-carrying 

 insects no self pollination takes place but pollen from short stamens is deposited 

 upon the stigmas of the short pistils and pollen from the long stamens is carried 

 to the stigmas of the long pistils. Cross pollination between two flowers of the 

 same form on a single plant may occur, but the arrangement assures a consider- 

 able amount of crossing between plants. It has been shown that when the pistils 

 of heterostyled plants are pollenized with pollen from the same flowers or from 

 other flowers containing stamens of an equal height the union may be fruitful 

 but is likely to be attended by varying degrees of sterility. ^^ This, however, 

 introduces the factor of incompatibility, about which more is said later. 

 Apparently heterostyly is relatively unimportant in determining setting in 

 deciduous fruits. 



Dichogamy : Protandry and Protogyny. — It has just been pointed out 

 that in heterostyled plants the sexes are nearly as completely separated 

 and self pollination as completely prevented as in monoecious plants. 

 Likewise there may be more or less separation of the sexes and a pre- 

 vention of self pollination in perfect flowered plants through the maturing 

 of the two sex elements at different times. This behavior of the plant 

 is known as dichogamy. If the stamens ripen before the pistil is ready 

 to receive pollen the flower is protogynous; if the reverse condition 

 holds it is protandrous. Dichogamy is incomplete when there is an 



