A. E. MURNEEK 335 



organic chemicals so far have been found effective in fruit setting. Of 

 these the naphthoxy and substituted phenoxy acids are especially potent 

 for this purpose. Many-seeded fruit evidently respond more readily 

 to stimulation in development by synthetic growth regulators than do 

 fruit containing a single seed. Desirable concentrations and the time and 

 mode of application have been studied extensively, particularly with 

 plants with which the greatest success has been secured so far. 



Tomatoes. — When tomatoes are grown in the greenhouse during 

 cloudy weather and/or subnormal temperature, or outdoors when the 

 nights are relatively cold, the number and size of the fruit can be 

 increased by the use of IB, NAA, and 4-chlorophenoxyacetic (CIPA) 

 acid, some of their homologues, and a number of other synthetic growth 

 regulators (41,58,61,97). The flowers are usually sprayed when in full 

 bloom or, preferably, after pollination and fertilization have occurred. 

 Pollen tube growth and fertilization, as noted before, in their aggregate 

 effect on growth of the ovary supplement the effects of synthetic growth 

 regulators on carpel development. There does not seem to be any 

 appreciable commercial value although there is a great deal of talk about 

 the production of seedless tomatoes. 



Tomato flowers are receptive to stimulation of this kind several days 

 after pollination. If whole plant spraying is practiced, which has been 

 shown to be even more effective than flower-cluster spraying (58, 61), 

 the spray must be so directed as to cover only that portion of the plant 

 containing mostly open flowers and young fruit. It has been observed 

 (58,61) and pointed out by Roberts and Struckmeyer (73) that spraying 

 tomato buds with growth regulators five or more days before pollination 

 gave a poor set and fruit of relatively small size. 



Hemphill (40) has recently completed a thorough investigation on 

 the time of application of three synthetic growth regulators at the 

 concentrations most desirable for increase of the tomato crop. When 

 applied eight days before anthesis pollen ceased to develop and collapsed 

 in the anthers, while spraying four days before full bloom often caused 

 premature pollen germination. The ovules were also detrimentally af- 

 fected when a growth regulator was applied as early as the bud stage. 

 They either ceased to develop and the embryo sacs disintegrated, or 

 those that did grow were greatly retarded in development. Seed forma- 

 tion was usually prevented. These results are in considerable agreement 

 with those obtained by Britten (10), who sprayed NAA on developing 



