210 CHEMICAL AGENTS AND GROWTH 



Table I. Effect of Gibberellin on Photoreversibility in Bean Hook 



Angular Response, Degrees 



° Red, 625-700 m^ for 15 min (250 mj/cm^). 

 6 Far red, 720-800 m/x for 25 min (12 mj/cm^). 



the hypocotyl hook in both hght and dark conditions in a manner 

 similar to that of auxin. 



Gibberellin brings about the same result whether the red activation 

 is given continuously over a 20-hr period or for only a brief interval. 

 The presence of gibberellin does not affect the reversal mechanism of 

 the hook, but is additive to the normal reversal action as indicated in 

 Table I. Table II presents evidence showing that gibberellin initiates 



Table II. Interaction of Gibberellin 



(10-6 M) and Red Radiant Energy 



(250 mj/cm^) on Elongation of Straight 



Section of Hypocotyl Hooks" 



Radiant Energy Elongation, cm 

 Dark 3.02 



Dark + gibberellin 3.30 



Red 2.92 



Red + gibberellin 3.19 



« L.S.D. 1% = 0.05. 



elongation responses in both light and dark conditions; also, that red 

 radiant energy initiates a separate response independent of gibberellin 

 and distinguishable from the sibberellin action. 



Kinetin 



Figure 3 presents the effect of kinetin on the hook response in dark- 

 ness and in red radiant energy. Kinetin induces a response very similar 

 to that of lAA, although the red is more effective in reducing the 

 negative response at higher concentrations. In general, the response is 

 similar to the effect of other growth regulators. 



