204 CHEMICAL AGENTS AND GROWTH 



In analogous experiments with kinetin, seeds were held at 22° for 

 12 hr in darkness interrupted after 2 hr with far-red and red light 

 treatments (Table IV). After the 12-hr period the seeds were trans- 



Table IV. Red Light Reversal of Far-Red Inhibition for 

 Kinetin-Treated Seeds Held at 22°C for 12 hr 



Germination after 36 hr at 7°, % 



Light Treatment" OM SXIQ-^M 



None 49 66 



Red 42 53 



Far red 5 3 



Far red -f red 28 42 



° Twenty minutes exposure to red or far red after second hour 

 at 22°. 



f erred in darkness to 7°, a temperature detrimental to further action of 

 kinetin. After 36 hr at 7°, it could be seen that kinetin had been in- 

 effective in reversing the far-red effect under conditions where red 

 light gave nearly complete reversal. 



The experiments summarized in Tables III and IV show that, under 

 given conditions, gibberellic acid or kinetin did not protect against the 

 inhibition of germination by far-red light, whereas subsequent exposure 

 to red light did. Thus the effect of the red, far-red photoreaction on the 

 germination of these seeds at 22° cannot be explained in terms of its 

 regulating the production of either endogenous gibberellin-like or 

 endogenous kinin-like substances. Moreover, the fact that the effects of 

 gibberellic acid plus kinetin on far-red treated seeds was less than 

 additive at 22° (Fig. \b) further suggests that the photoreaction can- 

 not be explained solely in terms of regulating the production of both 

 gibberellin and kinin. 



Whereas gibberellic acid or kinetin apparently reversed the far-red 

 effect during 40 hr at 22° (Fig. lb), they failed to do so when the 

 seeds were transferred after 12 hr at 22° to 37° or 7 °C, respectively 

 (Tables II-IV). One possible explanation is that the seeds begin to 

 respond to one or both of these chemicals at around 12 or more hr 

 after the beginning of imbibition. Alternatively, it is possible that one 

 or both of these agents was fully active within the first 12 hr, but that 

 its effect was reversed by the temperature change. 



