ZIMMERMAN: FORMATIVE INFLUENCES 107 



and halogen groups appear to be the most important. Some substituted benzoic 

 acids have a pronounced formative influence on plants but have little or no 

 effect on cell elongation. One compound of the group, however, induced both 

 cell elongation and modification of leaves (3, 7). Table 5 shows a list of active 

 and inactive compounds. 



Positions 2, 3, and 5 in the nucleus appeared to be the most important for 

 substitutions. For example, 2,3,5-triiodobenzoic acid and 2-chloro-3,5-diiodo- 

 benzoic acid had the most pronounced formative influence of any of the com- 

 pounds listed. In addition to modifying the pattern of leaves, they influence 

 flowering habit and correlation of organs (8). One to 5 mg. of triiodobenzoic 

 acid added to the soil of a 4-inch pot in which a tomato plant was growing was 

 sufficient to cause modification of growth of the stem, leaves, and flowers, to 

 cause axillary buds to grow flower clusters instead of the normal leafy shoots, 

 and to induce the terminal bud to terminate with a flower cluster instead of 

 continuing with a leafy shoot (Fig. 2 A and B). Similar results were obtained 

 by other methods of applying the chemical. It is effective as a lanolin prepara- 

 tion (1 to 10 mg./g. of lanolin), as a vapor applied in a closed container, and 

 as a water solution applied as a spray (25 to 100 mg./l.). 



The results obtained with 2-chloro-3,5-diiodobenzoic acid were similar to 

 but even more striking than those described for triiodobenzoic acid. Both com- 

 pounds caused the terminal bud and axillary buds of tomatoes to grow flower 

 clusters instead of leafy shoots, but the individual flowers were different. Those 

 which grew under the influence of 2-chloro-3,5-diiodobenzoic acid were small 

 with inconspicuous petals and sepals supported with an abnormally stout pedun- 

 cle (Fig. 3 A). As the chemical influence became weaker and the plants began 

 to recover, large single flowers instead of clusters were produced irregularly 

 along the stem. The small flowers did not set fruit but the large ones func- 

 tioned as normal flowers (Fig. 3 A and B). 



Another active substituted benzoic acid, 2-bromo-3-nitrobenzoic acid, is of 

 special interest since it caused both cell elongation (epinasty) and modified 

 leaves of tomato plants (7). It was not as active for cell elongation as some 

 of the phenoxy compounds but had a pronounced formative influence on growth. 

 2-Chloro-5-nitrobenzoic acid has a formative influence but does not cause cell 

 elongation. Judging from active benzoic acids listed in table 5 it would appear 



Explanation of figure 1 



Modification of organs induced with substituted phenoxy compounds. A. Tomato shoots : 

 left, control; right, response to spray with solution of /3-(2,4,6-trichlorophenoxy)-^'-chloro- 

 diethyl ether. B. Nicandra plants : left, control ; right, modifications induced with 2,4-dich- 

 lorophenoxyacetic acid (12.5 mg./l.). Solution applied at tip with nasal atomizer when 

 plant was 5 inches in height. Note non-modified leaves at base which were present when 

 treated. C. Enlarged leaves, buds, and flowers taken from plants in B. 



