Influence of Gibberellic Acid on lAA Disappearance 



635 



Table 1 . A summary of the sparing of indole-3-acetic acid destruction (+....) 

 obtained in Figures 2, 3, and 4. ( — ) Indicates no sparing action occurred. 



be noted that shades of opinion in rating the score {e.g.. Figure 2C 

 to be -f-? or Figure 3C to be + + ''') ^^^ "ot alter the final deductions 

 drawn. Table 1 shows that with apical tissue experiments carried out 

 in light (columns 3 and 5) there are sparing actions of almost all 

 magnitudes, whereas in the dark (colimms 4 and 6) sparing actions 

 are either absent or not marked. There is no sharp division between 

 experiments carried out in light and in darkness, but the largest spar- 

 ing actions are shown in the light. In contrast with this distribution 

 of sparing action, stem section experiments have an emphasis on 

 sparing in experiments carried out in the dark, while in light a single 

 experiment of low sparing permits no opinions to be formed. How- 

 ever, it may be noted that again no sharp division exists between 

 experiments carried out in light and in darkness. 



If one now views the light-mediated auxin destruction hypothesis 

 against the results of Table 1, it is evident that at least two disturb- 

 ing points prevent a satisfactory union between the two. The most 

 obvious lies in the sparing actions shown in the dark (column 2), 

 for with the above hypothesis sparing should not occur under these 

 conditions. The second concerns the marked variation in magnitude 

 of sparing actions referred to above. If GA were to intercede directly 

 in a light-operated hormone-destroying mechanism, one might rea- 

 sonably expect sparing actions to be present more consistently and to 

 be less variable in magnitude. 



Further hypotheses have been considered by Brian and Hemming 

 (5) to account for the enhancement of growth by GA. The possibility 

 that GA may combine with auxin(s) in the plant to form a more 

 active compound is considered and dismissed. Our own data do not 

 readily fit into any scheme based on this idea and it does not appear 

 to be a profitable line to pursue. Similarly, the possibility that GA 



