UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 491 



perfect flowering. The study of these flowering characteristics of the 

 persimmon and the ehissification of the more important of its varieties 

 has done much to explain the rather erratic behavior of this plant in 

 fruit setting and the maturing of seed-bearing or seedless fruits. 



Even more variable is the distribution of tlie sexes between different flowers 

 and different plants in the papaya. Higgins and Holf^" recognize 13 classes of 

 trees, depending on the combination or separation of stamens and pistils and on 

 form of the flower clusters, corolla and fruit. Independent of the classes based 

 on features other than sex distribution, these types are: 



1. Pure pistillate flowering plants. 



2. Pure staminate flowering plants. 



3. Plants producing both staminate and perfect flowers. 



4. Plants producing both staminate and perfect flowers, but with sterile 

 pollen. These might be called pseudo-hermaphrodite plants. 



5. Plants producing staminate and perfect flowers in which neither pistils 

 nor pollen are fertile. The plants might be called sterile hermaphrodites. 



G. Plants producing staminate, pistillate and perfect flowers. 



7. Plants producing pistillate and perfect flowers. 



8. Plants producing staminate and pistillate flowers. 



Tj^pes 2 and 5 are necessarily unfruitful, though type 5 is unfruitful appar- 

 ently because of incompatibiUty rather than impotence, for the sex organs are 

 developed but non-functioning. Types 1 and 4 are self unfruitful, though it is 

 possible that 4 is self barren because of incompatibility rather than impotence. 

 The other types are self fruitful; at least fruitfulness is not impossible because 

 of impotence. Some of these self fruitful types are dioecious, some are poly- 

 gamo-dicecious. Types 1 and 2 are by far the most common; that is, the papaya 

 is for the most part unisexual. Consequently in the average planting of that 

 fruit it is customary to retain a few of the staminate trees in order to insure a 

 good set of fruit on those bearing pistillate flowers. Of course staminate trees 

 remain barren, but if there should be only relatively few of them, they probably 

 would be valued more highly than an equal number of the fruit producers. 



The fig shows a distribution of its sexes somewhat less complicated than 

 the papaya; nevertheless this distribution should often be given careful 

 attention at the time of planting. Two kinds of flower clusters are borne 

 by fig trees. Certain bear pistillate flowers only. The standard fig 

 varieties include trees of this type exclusively. Certain other trees, 

 called "caprifigs, " produce both pistillate and staminate flowers within 

 the same cluster. As a rule, the staminate flowers are borne near the 

 "eye" of the fig and the pistillate flowers near its base. Fig trees may 

 thus be placed in two classes in respect to sex distribution, dioecious or 

 unisexual trees and monoecious trees. The pistillate flowering trees 

 alone produce the figs of commerce. The monoecious trees or caprifigs 

 are planted only for the purpose of furnishing pollen for the pistillate sorts. 

 Some authorities would take exception to certain of the statements just made 

 about the nature of fig flowers. Eisen^" states that there are three kinds of 



