104 PLANT GROWTH SUBSTANCES 



auxin; 3) the nitrogen of the amino acids is converted partly to asparagine 

 and partly to the protein of the cytoplasm; 4) these changes are in large 

 part prevented by all the three inhibitors. 



It is of interest that the process of cell elongation does involve con- 

 siderable synthesis of protein. It is also of interest that, while there are 

 definite differences, all three inhibitors act, at least qualitatively, in the 

 same way. This might well be expected for iodoacetate and arsenite, 

 since both are sulfhydryl reagents (11), but fluoride almost certainly 

 acts on another enzyme system and hence similarity between its action 

 and that of the others would hardly have been expected. 



Lastly it must be pointed out that these results, incomplete as they 

 are in themselves, are consistent with the idea that it is organic acid 

 metabolism which is primarily responsible for growth. For it is only by 

 way of the organic acids that the oxidation of sugars, the formation of 

 fats, and the conversion of amino acids to asparagine are linked. This 

 interpretation therefore agrees well with the concept put forward in an 

 earlier paper, that auxin acts on an enzyme concerned in four-carbon 

 acid metabolism. 



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2. Bonner, J.,/. Gen. Physiol., 20:1-11 (1936). 



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4. Christiansen, G. S., Kunz, L. J., Thimann, K. V., and Bonner, 



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5. Commoner, B. and Thimann, K. V., /. Gen. Physiol., 24:279-96 (1941). 



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