170 



A. POLJAKOFF-MAYBER 



IOt 

 8 



6' 



4- 







_, , ^ 



-HgO 



0.2 0.4 0.6 as 1.0 



IOt 

 8 



6f 



4 

 2 

 O.. 



B 



■HgO 



0.2 0.4 0.6 0.8 1.0 



Fig. 2. Histograms showing the chromatographic separation of unchilled 



and chilled Fraxinus seeds. The bioassay used was Fraxinus embryo 



germination test. The broken line gives the water controls ^°. 



dry lettuce seeds and seeds imbibed in water in the dark contain 

 germination inhibitors. On imbibition in water, the acid 

 inhibitors disappear just before the actual germination begins, 

 the neutral inhibitors being still present. This may explain the 

 low germination percentage in the dark. On imbibition in 

 coumarin, coumarin accumulates in the seeds^^ and apparently 

 blocks germination. Comparison of the various histograms 

 suggests that some of the natural inhibitors may also be coumarin 

 derivatives. In another case^^ a natural germination inhibitor 

 present in the seeds of TrigoneUa arabica was identified as 

 coumarin. 



