S. H. WITTWER 367 



exists, however, pertaining to results that can be expected by the use 

 of growth substances on many economic crops which exhibit from time 

 to time difficulties in natural fruit setting. Most issues could be reconciled 

 by a proper consideration of the effects of differing environments. To 

 date, an almost total disregard of the importance of prevailing weather 

 in determining fruit setting response to hormone chemicals has left a 

 confused and somewhat distorted picture, making it extremely difficult 

 to interpret many of the contradictory reports. The most profound 

 increases in yield and fruit setting on crops reported as responding to 

 the apphcation of growth substances are obtained when the prevailing 

 environment is not conducive to good fruit set. 



Fruit Set in Tomatoes. — In at least one crop, the tomato, naturally 

 produced hormones responsible for fruit set can be completely replaced 

 by a great number of synthetic chemicals (18,45,58). These materials 

 may be applied externally to the floral parts by several methods. Yet, 

 even in the tomato the responses to hormone treatment, as measured 

 by yield and fruit size increases, have not been consistent. 



The significance of variety and season on fruit production In green- 

 house tomatoes as they relate to the changing day-to-day pattern of 

 solar radiation has been emphasized (54). The effects of these variables 

 on yield and fruit size are presented in Table i. That yields in the 



TABLE 1 



Effects of fruit setting treatments on yield and fruit size of greenhouse 

 tomatoes as conditioned by variety and season 



*Flower clusters sprayed with a mixture consisting of 10 ppm of p-chloro- 

 phenoxyacetic acid (CIPA) and 30 ppm. of P-naphthoxyacetic acid (NOA). 



