Influence of Gibbcrcllic Acid on lAA Disappearance 



631 



showed an enhanced rate of lAA destruction with GA over part of 

 the experimental period. In no experiment did GA exert a sparing 

 action. 



Experiments With Stem Sections 



During the summer of 1957 extensive preliminary experiments 

 were carried out with stem sections, following their use by Brian and 

 Hemming (4), to investigate whether GA influences rates of lAA 

 destruction when sections are incubated in solutions of hormone. 

 Sections were cut serially from the entire length of stems of light- 

 grown plants and were randomized before use. Rather variable spar- 

 ing action results were obtained which, apart from variation caused 

 by restricted sampling of sections, suggested that tissues of different 

 physiological ages and states should be separated. This was done 

 in all the following exj^eriments carried out during the summer of 

 1958. 



Results of experiments in the dark with sections from dark-grown 

 plants are shown in Figure 2. Results in Figure 2C were obtained 

 with 'Alaska' pea. A sparing of lAA destruction with GA was ob- 

 tained in all experiments; however, in Figure 2B it was appreciable 

 while in Figure 2A it was smaller, and in Figure 2C it was present 

 over approximately only a 3 hr. period. 



0.3 



TIME IN HOURS 



Fig. 2. Rate of destruction of indole-3-acetic acid by pea stem sections in the 

 piesence (solid lines) and absence (broken lines) of gibberellic acid in darkness 

 (A, B, C) and in light (D). 'Alaska' peas were used for the experiment in C and 

 'Progress No. 9' for the remainder. 



