On form and function of plant growth substances 



in the straight growth test (see Figure 3 and Table 1). So apparently the 

 restriction of substitution in the 4-position is not an absolute one, but one of 

 maximal (very small) size of the substituent. 



{a) Figure 3. Pea test. (h) 



{a) 2:3:6-trichlorobenzoic acid: 50,25, W. 4.\0~'^ moljl. 

 {b) VII: 50, 25, 10, 4.10-5 wo///. 



When surveying the available data on substituted benzoic acids, in our 

 opinion the most plausible conclusions can be summarized as follows: 



(i) Activity is dependent on a non-flat structure, caused by diortho 

 substituents of such a size that the COOH group is 7iot masked. 



Table 1 



Avena straight growth. Percentage elongation. The mean of 20 sections of initial length 4 mm, 



measured after 24:-hour test 



121 



