GERMINATION OF LETTUCE SEED 199 



RESULTS AND DISCUSSION 



1. Separation of the Gibberellic Acid from the Kinetin Effect by 

 Temperature and Evidence for the Distinct Effects of These Com- 

 pounds on Germination. Effects of gibberellic acid and kinetin on 

 germination at 35 °C are illustrated in Fig. la. Kinetin promoted 

 germination over water controls at this temperature; gibberellic acid 

 had no effect. The concentration of 5 X 10"''M kinetin used in this 

 experiment was optimal at this temperature. No concentration of gib- 

 berellic acid increased germination over water controls. Germination 

 was greater with the combination of gibberellic acid and kinetin than 

 with kinetin alone. This synergism suggests that gibberellic acid some- 

 how retained the capacity to affect cellular processes in conjunction 

 with kinetin at 35 °C, even though gibberellic acid alone had no ap- 

 parent effect on germination. A direct test demonstrating that gib- 

 berellic acid was not irreversibly inactivated by high temperature was 

 made. Dishes containing seeds with 3 X lO'^M gibberellic acid or 

 none at all were left in darkness at 37 °C for 48 hr. The dishes were 

 then transferred, in darkness, to a room at 22° and examined 24 hr 

 later. At that time, 86% of the seeds treated with the gibberellic acid 

 had germinated, compared with 12% of the similarly treated water 

 controls. These last results agree with those of Kahn et al. (1957), 

 which show that germination of certain seeds at 2 1 ° was decreased by 

 similar pretreatment at 36° and that gibberellin reversed this in- 

 hibition. 



It has been reported that gibberellin or kinin can stimulate germina- 

 tion of Grand Rapids seeds at room temperature either in darkness or 

 with far-red treatment (Kahn et al, 1957; Miller, 1956). Since germ- 

 ination was very rapid at 22 °C, it was desirable to give the seeds at 

 this temperature a saturating exposure to far-red light (Borthwick 

 et al., 1954) to slow the germination so that differences in germina- 

 tion rates caused by gibberellic acid or kinetin could be more ac- 

 curately observed. The optimal concentrations for stimulating germina- 

 tion of seeds so treated were 3 X \0~^M for gibberellic acid and 5 

 X 10~^M (as at 35 °C) for kinetin. In the presence of these optimal 



