A. E. MURNEEK 34^ 



of an extensive survey of fruit setting of the Delicious apple, Gardner 

 et al. (29) reached the conclusion that during the critical period of one 

 to two weeks after full bloom the young fruit apparently is very sensitive 

 and may abort easily if the environment, primarily temperature and 

 sunlight, is not favorable. Of even greater interest is the contention 

 that certain fungicides, used for scab control at this early period, may 

 also have a profound effect on fruit set of this variety. 



Luckwell (49) has made a seasonal study of the hormone content 

 of apple seeds in relation to endosperm development. The concentrated 

 ether extracts from whole seeds and separately from embryos and endo- 

 sperm-nucellar tissues (older seeds) were tested for their potency to 

 produce parthenocarpic tomato fruit. The hormone concentration was 

 about 18 times as high in endosperm-nucellar tissues as in the embryo. 

 And since the nucellus constituted only a minor fraction of the sample, 

 the author thinks that the hormone came chiefly from the endosperm. 

 During the period of the usual postfertihzation abscission of apples 

 (53,20) the hormone content was of a relatively low concentration. 

 Luckwell expresses the view that the hormone found in endosperm 

 seems to prevent fruit abscission. Does it mean that a hormone released 

 by endosperm, in preventing abscission, would thereby help to maintain 

 or increase the food supply to the seeds and fruit? 



Naphthaleneacetic acid, at the relatively high concentration used for 

 apple and peach thinning, most likely disturbed the endosperm and 

 possibly also the embryo in their physiological relationships during 

 the critical period of early seed development. This effect may be a 

 direct one or, less likely, through stimulation of excessive growth of the 

 pericarp. Studies by Swanson et al. (83) on ovule abortion in Tradescantia, 

 as disturbed by a 2,4-D spray, suggested that the younger the ovule the 

 more harmful was the spray and that endosperm was inhibited in rela- 

 tively mature seeds. Ovule collapse followed disintegration of the endo- 

 sperm and the chalaza. Still later the nucellus and integuments collapsed. 



Preliminary observations by us of apple fruit thinned by means of 

 NAA indicated invariably an effect on the seed, endosperm, and nucellus, 

 which had collapsed. This probably was the cause of abscission of large 

 numbers of the young fruit. Very probably the specimens that abscissed 

 were most sensitive to the treatment due to the presence of fewer 

 seeds or seeds with less developed endosperm because of partial pollina- 

 tion or pollination with less compatible pollen. Fruit borne on spurs 



