GERMINATION OF LETTUCE SEED 201 



or kinetin at the lower concentrations promoted germination over 

 water controls, the increase effected by the combination was much less 

 than the sum of the increases effected by each alone under these con- 

 ditions. This is in contrast to the synergism observed at 35 °C. 



Effects of gibberellic acid and kinetin on termination at 17°C are 

 illustrated in Fig. Ic. Kinetin alone did not promote germination over 

 water controls at this temperature, but gibberellic acid did. The com- 

 bination of gibberellic acid plus kinetin, however, did not promote 

 germination over water controls at this temperature. Thus, although 

 kinetin alone did not seem to affect germination rate, it did appear to 

 cancel the effect of gibberellic acid at this temperature. 



Effects of gibberellic acid and kinetin on germination at 7°C are 

 shown in Fig. \d. As at 17°, gibberellic acid promoted germination 

 over similarly treated water controls and kinetin did not. In the pres- 

 ence of the combination of gibberellic acid plus kinetin, however, 

 termination was about the same as with gibberellic acid alone. At 7°, 

 kinetin did not affect the germination rate and did not modify the 

 overall response of the seeds to gibberellic acid. 



GibbereUic acid alone did not stimulate germination over similarly 

 treated water controls at 35°C, but did so at 22°, 17°, and 7°C. 

 Kinetin alone stimulated germination over similarly treated water con- 

 trols at 35° and 22°, but did not at 17° and 7'C. These results indi- 

 cate that temperature can be used as a means of separating gibberellic 

 acid and kinetin effects in the overall germination process. This sug- 

 gests that gibberellic acid and kinetin affect germination by distinct 

 mechanisms, but it does not in itself rule out the hypothesis that gib- 

 berellic acid and kinetin ultimately affect the same basic process (es) 

 controlling germination. 



At 35 °C, gibberellic acid did not promote germination in the ab- 

 sence of kinetin, but did in its presence. This effect was observed even 

 in the presence of kinetin at optimal concentration for promoting 

 germination at this temperature. At 17°, gibberellic acid promoted 

 germination in the absence of kinetin but not in its presence. The quite 

 different apparent interactions of gibberellic acid plus kinetin at 35°, 

 22°, and 17° provide presumptive evidence against the hypothesis that 

 gibberellic acid and kinetin affect the same process (es) controlling 

 germination. A more likely possibility is that gibberellic acid and 



