Chemical configuration and action. Paste method 



nitrile tested, both of which gave the same resuks. I also wish to thank 

 Dr. J. A. Bentley of Manchester, who sent samples of 2:3:6-trichlorobenzoic 

 acid and 2:3:6-trichlorobenzaldehyde, and, for comparison with these, the 



Figure 2. The concentration-action 

 curves of some halogen-substituted 

 benzoic acids and aldehydes in com- 

 parison with indole-3-acetic acid. 



TBA = trichlorobenzaldehyde ; 



TBS = trichlorobenzoic acid; 



lAA = indole-3-acetic acid. 



V 6 'TBA 



2 9 5 'TBA 



3 9 5-TBA 



log concn. 



2:4:6-, the 2:4:5-, and the 3:4:5-trichlorobenzaldehyde. The first two 

 substances, as observed by Bentley (1950) showed growth-promoting activity, 

 but nearly ten times less than indole-3-acetic acid, whereas the other three 

 trichloroaldehydes showed a small activity as growth inhibitors [Figure 2). 





+eo 



\¥0 



I 



S: 

 to 



'20 



Figure 3. The concentration-action 

 curves of 'N-dimethylthiuramacetic acid 

 (ND TE) , NN-dimethylthiurampro- 

 pionic acid (NDTP), and indole-3- 

 acetic acid {I A A) in the paste test. 



log concn. 



10" 



The newly discovered growth substance iViV-dimethylthiuramacetic acid 

 (Kerk, 1955) was kindly provided by Dr. van der Veen of Eindhoven. This 

 gave a small growth-promoting activity in the paste test [Figure 3) nearly 



143 



