514 FUNDAMENTALS OF FRUIT PRODUCTION 



grape vine (F. riparia X V. labrusca) which fruited only twice during a 

 30-ycar period, "the pistils evidently varying in strength but being gener- 

 ally too weak to produce fruit. "^ Though the date palm is usually 

 monoecious, still a tree that ordinarily produces pistillate flowers only may 

 develop occasionally a cluster of staminate flowers, or perhaps one year 

 produce a few hermaphrodite flowers and never do so again. ^^^ Certain 

 varieties of the Japanese persimmon show great variation in the kinds 

 of flowers they bear from year to year. 2"; ^o jj^ some seasons they 

 produce pistillate flowers only and in other seasons they produce a num- 

 ber of staminate flowers along with the pistillates. "Seedling (per- 

 simmon) trees are very unreliable in the production of blossoms, bearing 

 male flowers during the first few years, then a small proportion of female 

 flowers, while later the appearance of male flowers is sporadic on some 

 trees and regular on others. "2" 



Age and Vigor of Plant. — Practically inseparable from the influences 

 on fruit setting of nutritive conditions within the plant, of nutrient 

 supply without, of locality and of season, is that of age and vigor. The 

 change from the production of staminate flowers only to that of some 

 staminate and some pistillate flowers and later of pistillate flowers only, 

 mentioned in a preceding paragraph as common in seedlings of the 

 Japanese persimmon, is a case in point. Young vigorous apple trees 

 often fail to set fruit under controfled cross pollinations, when older and 

 less vigorous trees of the same varieties set freely. ^"'^ Waugh^^* found on 

 the average a higher percentage of defective pistils in young and vigorous 

 plum trees than in older trees of the same kinds. The Muscat of Alex- 

 andria grape is reported to show marked susceptibility to "coulure" or 

 dropping for the year or two after starting to bear, but later this trouble 

 is much less serious.^ Young grape vines have been found to produce 

 less pollen than mature vines of the same variety.^ 



In the instances cited, age of plant has been the factor apparently 

 associated with the degree or percentage of fruit setting. It is probable, 

 however, that age is effective through its influence on vigor and the 

 internal conditions of nutrition or hybridity with which vigor is asso- 

 ciated. It is interesting that Stout found self compatibility in chicory 

 entirely independent of differences in vegetative vigor, thus suggesting 

 that some of the internal factors controlling fruit setting and fertility are 

 not influenced by vigor. As in the cases where fruitfulness is influenced 

 by variations in nutritive conditions, nutrient supply, locality and season, 

 most of the influence of varying age and vigor seems to be through 

 effects on impotence preceding fertilization and embryo abortion at a 

 later stage and not on compatibility, using that term in its narrower 

 sense. 



Temperature. — The general effect on the setting of fruit of tempera- 

 tures slightly below freezing just before, at or shortly after blossoming is 



