202 CHEMICAL AGENTS AND GROWTH 



kinetin affect different (groups of) processes that share in the regula- 

 tion of germination. 



2. Separation of Red Light Effect from Either Gibberellic Acid or 

 Kinetin Effect. Seeds germinated for 36 hr at 7°C gave 0% germina- 

 tion, owing to the slow rate of germination at this temperature (Table 

 I). Seeds germinated at 37° gave 0% germination regardless of the 



Table I. Germination at 37° or 7° after Holding at 22°C'' 



Percentage Germination 



" Seeds were always in darkness during these experiments. 



length of the experiment or the concentration of gibberellic acid. How- 

 ever, seeds will germinate in water under these unfavorable conditions 

 if they are first held in darkness at 22 ^C for some time (Table I). 

 Presumably, changes occur in the seeds during the 8 or 12 hr at 22° 

 and lead to subsequent germination at 37° and an increased rate of 

 germination at 7°. Effects of gibberellic acid, kinetin, or light treat- 

 ments on seeds during the first 12 hr at 22° could conceivably be 

 separated by transferring the seeds after the 12 hr to the temperature 

 unfavorable for further action of either chemical on germination — 37° 

 to inhibit further action of gibberellic acid or 7° to inhibit the action 

 of kinetin. 



For experiments run entirely at room temperature, Kahn et al. 

 (1957) pointed out that "since gibberellin that has entered the seeds 

 cannot be removed, the lack of reversal of the gibberellin effect by 

 far red light cannot be considered definitive." In an attempt to perform 

 a definitive experiment, we held seeds for the first 12 hr at 22 °C in the 

 presence of 3 X lO'^M gibberellic acid and exposed them to 20 min 

 of far-red fight at various times during this period. They were then 

 transferred in darkness to a 37° incubator; this treatment might be 

 considered tantamount to removing the gibberellic acid that had en- 



