526 FUNDAMENTALS OF FRUIT PRODUCTION 



about 25 per cent, of the fruits of the Blue Damson plums contained good 

 plump seeds. ^^ The remaining 75 per cent, were seedless or their seeds 

 were only half grown and non-viable. Many other plum varieties were 

 found to bear a large percentage of seedless fruits. Nevertheless, none 

 of these varieties developed fruit parthenocarpically and in some of them 

 cross pollination was necessary for any set at all. " The kind of pollen used 

 seems to have had little bearing upon the relationship of fruit production 

 to seed production, as the percentage of seeds developed in any variety 

 seems to be rather constant regardless of the kind of pollen used."^^ 

 The same type of seedlessness has been observed in many sweet cherry 

 varieties, in the May Duke cherry reaching sometimes over 95 per cent, 

 of the fruits. Seedlessness that is not associated with parthenocarpy is 

 likewise frequent in some of the cultivated varieties of the filbert, where 

 it is a serious matter since seeds constitute the crop. A thorough study 

 would undoubtedly show that seedlessness is frequently associated 

 with embryo abortion in the developing seeds of many cultivated fruits. 

 Though in many varieties if seed abortion takes place at any stage 

 the fruit drops prematurely, in many others it can occur at a late, and 

 still others at an early, stage and still the fruit will persist and mature 

 properly. Evidently seedlessness from this cause depends on the 

 varying requirements of the ovarian tissues of different fruits for the 

 stimulus imparted to them by the growth of the partly developed 

 seeds within. Instances of this kind, however, probably always follow 

 fertilization. 



Vegetative and Stimulative Parthenocarpy. — Distinction has been 

 made between vegetative or autonomic and stimulative or aitionomic 

 parthenocarpy. In certain species parthenocarpic development is 

 vegetative; in other species it is stimulative; in still others both kinds 

 occur. The cases of parthenocarpy that have been reported for a number 

 of species have not been studied carefully enough to make possible 

 their classification. Among the fruits reported as vegetatively partheno- 

 carpic may be mentioned the banana,^ many varieties of the Japanese 

 persimmon, ''°' ^^ certain mulberries, ^^ certain peach varieties, ^^^ the 

 medlar, ^2 i\yQ papaya,*^^ the egg plant, summer squash and the English 

 cucumber, ^^ a number of varieties of the orange^^*' and many varieties 

 of the fig.'*'' These fruits, or certain of their varieties, either occasionally 

 or regularly set and mature fruit without the stimulus even of pollination. 

 Among those that have been reported parthenocarpic when subjected to 

 certain stimuli, usually the stimulus of pollination, are the pepino,'*^ 

 tobacco, *^^ pear^^^ and Jerusalem cherry. ^^^ Many varieties of Musca- 

 dine^^" and of Labrusca and Labrusca-hybrid grapes^ have been reported 

 as occasionally or sparingly parthenocarpic when subjected to the stimu- 

 lus of pollination with impotent pollen, and the Thompson Seedless^^ grape 

 is regularly parthenocarpic under similiar conditions. 



