Physiological and Anatomical Effects 131 



sary for the complete respiration of pyruvic acid to carbon dioxide 

 have been tested for auxin sensitivity (Price et al, unpublished). Inter- 

 estingly enough, essentially no response to the auxins was obtained. 

 This suggests that the eflEect of auxin on respiration may not be 

 through an effect on enzymes involved in pyruvate metabolism. This 

 observation has been used as indirect support for the hypothesis that 

 auxin acts principally through a phosphate transfer system (Bonner 

 and Bandurski, 1952). 



TIME 



Fig. 59. A comparison of the effects of auxin (3.5 mg./l. indoleacetic acid) upon 

 ascorbic oxidase activity and growth of excised tobacco pith tissue. Sohd symbols 

 represent controls, hollow symbols auxin treated; continuous lines represent ascorbic 

 oxidase activity, dashed lines growth (from Newcombe, 1951). 



EFFECTS ON PLANT CONSTITUENTS 



Auxins may have very different efllects on the constituents of 

 plants, depending upon the concentration of auxin applied. For this 



