S. H. WITTWER 375 



vestigations, Mitchell et al. (28) have reported a decided improvement 

 in the retention of vitamin C and moisture in snap beans during storage 

 when CIPA at 400 ppm. was used not as a spray designed for improving 

 fruit set, but as a spray treatment applied four days prior to harvest. 

 Additional studies should be made on the effects of growth substances 

 on postharvest quality and shelf-life of such perishables as beans, peas, 

 sweet corn, and asparagus. 



The use of growth substances for improving fruit set and seed pro- 

 duction as an aid in plant breeding has attracted an increasing interest 

 on a great variety of crops. The work of Whitaker and Pryor (52) with 

 melons, Schomer and Hamner (40) with berries, Emsweller and Stewart 

 (12) with lilies, and Wester and Marth (51) with Hma beans indicates 

 that growth substances may increase both the number of successful 

 crosses and the number of seeds per cross, and that they may also help 

 overcome certain incompatibilities and assist in special types of vegetative 

 propagations. Why seed production with some crops is stimulated while 

 in other crops, and in some instances the same crop (51,55), with similar 

 treatments it is retarded is hard to reconcile. Time and method of 

 application are undoubtedly factors, as well as the prevention of abscission 

 of the young fruit. Perhaps stimulatory effects of the growth substances 

 on pollen germination and tube growth, as suggested by Eyster (13), 

 and the data of Addicot (i), offer a partial explanation. Using identical 

 treatments of growth substances, our results with hormone spraying 

 of snap beans show marked decreases in seed content on some plantings 

 and in others significant increases. 



One of the most puzzling series of reports is the failure of the known 

 growth substances in effecting fruit set on such tree fruits as the apple, 

 pear, peach, plum, and cherry. Insofar as the author is aware, only one 

 (46) of many who have investigated the possibilities in this field has 

 reported positive results. Lewis (25) has summarized papers published 

 on the stimulation of fruit development with chemicals by the statement 

 that many-seeded fruits, such as tomatoes, cucurbits, and Oenothera 

 are stimulated, whereas in few-seeded fruits, such as cherries, plums, 

 pears, and apples, fruits are not formed. A possible exception to the rule 

 is the snap bean pod, a few-seeded fruit, which is definitely stimulated. 



Plant reproductive organs, especially the pollen and young fruit, 

 offer interesting possibilities as source material for the isolation of new 

 plant growth substances. Growth hormones occur in these tissues in 



