i8o 



PLANT GROWTH SUBSTANCES 



of tomatoes were induced to grow from axillary buds where leafy shoots 

 normally appear and that terminal buds were replaced with flower 

 clusters. The usual flower clusters also developed along the stem. The 

 treated plants lost much of their apical dominance and produced an 

 abnormally large number of axillary leafy branches. It was further 

 pointed out that though benzoic acid was physiologically inactive, the 

 molecule could be activated by the substitution of amino groups or 

 halogen atoms in the ring (7,10,11,12), The positions 2, 3, and 5 of the 

 nucleus appeared to be the most important for substitutions. None of 

 the mono-substituted compounds tested was found active. 2,5-Diiodo- 

 benzoic acid was active for modification and pattern of leaves but 

 did not induce axillary flowers. 2,3,5-Triiodobenzoic acid induced forma- 

 tive effects and also modified the position of flower clusters. 2-Amino- 

 3,5-diiodobenzoic acid was inactive, but 2-chloro-3,5-diiodobenzoic acid 

 was very active resembling 2,3,5-triiodobenzoic acid (11). 2,3,6-Tri- 

 chlorobenzoic acid causes cell elongation, initiates roots, and modifies 

 leaves. The molecular configuration as a whole rather than any part of 

 the molecule appeared to determine physiological activity. 



Galston (4) attempted to initiate flowering of soybeans by the use of 

 2,3,5-triiodobenzoic acid. Though he succeeded in increasing the number 

 of flowers per plant from 32 on the control to 181 on the treated plant, 

 Galston states that 2,3,5-triiodobenzoic acid does not possess florigenetic 

 properties since it will not induce vegetative soybean plants to flower. 

 He further stated that 2,3,5-triiodobenzoic acid caused morphological 

 responses such as shortening of the internodes, loss of apical dominance, 

 epinasty of young leaves, and so on, but that the chemical itself was 

 without auxin activity. The latter conclusion perhaps was drawn from 

 the fact that 2,3,5-triiodobenzoic acid is not active on the Avena 

 coleoptile. 



Tumanov and Lizandr (8) found that 2,3,5-triiodobenzoic acid re- 

 tarded growth of Perilla and caused formative effects. Alfalfa was more 

 sensitive than Perilla. These authors found a difference in sensitivity dur- 

 ing short and long days. The treatment caused a variation in the number 

 and size of leaflets in alfalfa. Spraying with weaker solutions, 0.005 P^^ 

 cent, in long days brought about increased yield of alfalfa seed. Flax and 

 sunflower species showed notable changes in growth when treated with 

 0.0 1 per cent solution. This concentration also caused peas to branch 

 through stimulation of axial buds and fusing of leaflets. There was, how- 



