632 



5. Housley and B. J. Deverall 



One experiment was carried out with dark-grown material in 

 light under fluorescent tubes (Figure 2D). GA treatment resulted 

 in a small but consistent sparing of lAA destruction. 



Experiments With Stem Apices 



Results of experiments with apical tissues are shown in Figures 3 

 and 4. Several curves differ from those of Figure 2 in being convex 

 rather than concave upwards; the rate of disappearance of lAA tends 

 to increase with time rather than decrease. Experiments carried out 

 in the dark with tissues from dark-grown (Figure 3A, B, C) and light- 

 grown plants (Figure 3D) show, with the exception of Figure 3C, no 

 sparing of lAA destruction with GA; in Figure 3C there is a tendency 

 to sparing. In Figure 3A and B it is thought that the separation of the 

 curves after approximately 4 and 2.5 hrs., respectively, resulted from 

 accidental removal of apical tissues from the hormone solutions during 

 shaking in the dark (this occurred only with apical tissues, and when 

 the volume of experimental solution became small). 



In contrast with the above experiments in the dark, experiments 

 in the light using apices from dark-grown (Figure 4A and B) and 

 light-grown plants (Figure 4C to F) show a greater range of lAA spar- 

 ing. Marked sparing is shown in Figure 4C, while in the remainder 

 of the experiments there is a progressive decrease until, in Figure 4F 

 and possibly in Figure 4D, no lAA sparing occurs. 



0.3 



TIME IN HOURS 



Fig. 3. Rate of ilcstiuction of ind()lc-3-acciic acid by apical pea stem tissues with 

 (solid lines) and without (broken lines) gibbeiellic acid in darkness. Plants grown 

 in darkness (A, B, C) and in light (D). 



