p. W. ZIMMERMAN l8l 



ever, no definite sign that 2,3,5-triiodobenzoic acid could be considered 

 as having florigenetic properties. 



Owen (6) treated a number of species with 2,3,5-triiodobenzoic acid 

 and brought about distortions of leaves, stems, and flowers but failed 

 to change any organ from the vegetative to the flowering stage. Avery 

 and Johnson (i) say that the induction of flowers with 2,3,5-triiodo- 

 benzoic acid in place of vegetative tissue in tomato strongly suggests 

 that the substance plays the role of flower-inducing hormones in some 

 plants. 



The best support for the earlier findings of Zimmerman and Hitch- 

 cock was published by Waard and Roodenburg (9). These workers found 

 that the treatment with 2,3,5-triiodobenzoic acid caused the flower 

 cluster to develop at the top of the plant while the vegetative shoot was 

 suppressed. This was considered as a shifting of the correlative relations 

 between the vegetative shoot and flower cluster. They also reported an 

 increase in the number of initiated flower buds and the formation of 

 axillary flower buds when the plants had very few leaves. In fact the 

 illustration shows the flower buds arising from plants with only cotyledon 

 leaves. They concluded that the chemical has the property of starting 

 the process of flower formation and also that it is possible to shorten the 

 vegetative juvenile stage of tomatoes. 



In contrast with the case in the substituted phenoxy acids, the para 

 position is not an important location in the molecular configuration for 

 active derivatives of benzoic acid. Not all possible substitutions have 

 been made, but from the information at hand the halogen substitutions 

 in the 2, 3, 5, and 6 positions make the molecule more active than the 

 substitution of amino or nitro groups. For example, 2-amino-3,5-di- 

 chlorobenzoic acid is inactive while 2-chloro-3,5-diiodobenzoic acid is 

 very active for modification of leaves and induction of axillary flower 

 clusters. 2,5-Dichlorobenzoic acid is especially active for inducing par- 

 thenocarpic fruit and modified leaves but does not induce axillary or 

 terminal flower clusters. 



Since the effects of 2,3,5-triiodobenzoic acid vary in summer and 

 winter with the rate of growth of tomato plants, it is evident that the 

 substance cannot work alone. It must depend upon materials made by 

 the plant in order to cause vegetative tissue to produce flowers. It is 

 assumed that plant hormones in general require supporting substances 

 produced by the plant to cause well-known physiological responses. 



