132 Fundamentals of Auxin Action 



reason it would seem worthwhile to discuss the elTects of low or 

 l)hysiologi(al concentrations of auxins separately, and then turn to 

 the effects of stronger treatments. 



Auxins affect the nucleic acids of plants (Silberger and Skoog, 

 1953). Both the ribose-nucleic acids and the desoxyribose nucleic acids 

 were found to increase following the addition of from 0.01 to 10 

 mg./liter of indoleacetic acid to tobacco pith tissue in sterile culture. 



400 



300 



O 



260 ^ 



X 



-I 100 tr) 



LU 



or 



10 MG/L 



CONC. OF AUXIN 



Fig. 60. The relationship between the stimulation of growth by auxin (indole- 

 acetic acid) and some changes in carbohydrate constituents of excised tobacco stem 

 sections (Skoog and Robinson, 1950). 



The increases were complete in the first four days, and growth in- 

 creases which were very comparable to the ribose-nucleic acid increases 

 followed in the next three days. 



Changes in reducing sugars after auxin treatment have been noted 

 by several workers, and sometimes these changes show striking similari- 

 ties to the growth responses. An example of this is shown in figure 60. 

 It appears from these data that the increase in sugars is not due to an 



