Parthenocarpy 229 



formed fruits. The auxin sprays force many abnormal flowers (which 

 would naturally abscise) to set fruit instead. This results in a higher 

 proportion of deformed fruits, particularly by setting of fasciated 

 flowers with multiple ovaries (Mann and Minges, 1949). 



Several reports indicate that hollow locules or puffy fruit are some- 

 times associated with auxin treatments as well as abnormally green 

 locules (Howlett, 1949). Studies on nitrogen nutrition of the tomato 

 have indicated that both puffiness and green locules are associated with 

 excessive nitrogen fertilization, and the use of auxin sprays only accen- 

 tuates these difficulties when the inherent condition for their expres- 

 sion already exists (Leopold and Guernsey, 1953). It was reported that 

 restricting the auxin solution to the face or front of the flowers could 

 considerably alleviate the tendencies toward deformed fruits. 



There is some evidence that auxin treatments can actually cause 

 the abortion of young embryos in the fruit and produce seedlessness 

 in spite of pollination (Singletary, 1950). For this reason, use of auxins 

 to force fruit-set in crops in which the seeds are important is seldom 

 effective (e.g. seed beans and shell peas). 



Another difficulty resulting from auxin treatments is the occur- 

 rence of relatively fragile carpel walls on the fruit. These walls make 

 the fruit more susceptible to bruising, and for this reason there have 

 been reports of "prematiue softening" of parthenocarpic tomatoes 

 (Howlett, 1949). Marketed parthenocarpic fruit held at 70° F softened 

 two to four days earlier than pollinated fruit; however, if pollen and 

 auxin were both used to set the fruit then the condition of premature 

 softening did not occur. There is indication that the use of different aux- 

 ins may overcome the problem of thin-walled fruits as Howlett (1950) 

 has reported. He found that a-2,3,5-trichlorophenoxypropionic acid 

 may set fruit with walls as sturdy as pollinated fruits. 



CONCLUSIONS 



It may be said in summary that auxins will not increase fruit-set 

 unless a limitation of fruit-set exists at the time of use. Recognized 

 limitations which may make the use of auxins feasible are weak light, 

 excessively high or low temperatures, high nitrogen content, low leaf 

 areas, and conditions of excessive flower abscission. Auxins will increase 

 early yields in tomatoes by overcoming these limitations of fruit-set 

 which commonly exist in winter greenhouse conditions and in the 

 early spring field plantings. Hastening of maturity of the fruits will 

 also contribute to the production of early yields. 



It is clear from the studies of fruit-set which have been carried out 

 that not only is auxin essential to fruit-set, but nutrient substrates for 



