184 



S. KLEIN 



100 



90 

 c 

 O 60- 



O 70 



£ 60 



1 A 



-o^ 



5 7.5 10 12.5 15 

 mg % DNP 



12.5 15 



mg 7o DNP 



Fig. 1. Germination percentage of lettuce seeds (Grand Rapids) in different 



concentrations of dinitrophenol. 1 A: absolute germination percentages; 



1 B: germination percentages related to the germination percentage in water 



as 100. ( ) after illumination; ( ) in darkness. 



100 



c 90 

 O 



■.^; 80 

 o 

 .E 70 



E 60 

 *^ 50 

 o 40 



1.0 2.0 3.0 4.0 

 mg "/o Coumarin 



2.0 2.5 3.0 3.5 4.0 4.5 5.0 



mg "/o Coumarin 



Fig. 2. Germination of lettuce seeds in different concentrations of coumarin. 



Explanation as in Fig. 1. 



germination. Comparing the effect of coumarin with that of 

 dinitrophenol, both of which are germination inhibitors, Figs. 

 1 and 2 show the amount of seeds germinating as a function of 

 various concentrations after a Hght treatment and in darkness. 

 Since the percentage of germination of light-treated seeds is 

 always higher than of seeds kept in darkness, this seems to 

 indicate that light can to some extent overcome the effects of 



