102 P. f- Wareing and T. A. Villiers 



chilled seeds. The subsequent growth of unchilled embryos stimulated 

 to germinate in this way appears to be normal. 



It seems clear that the extracts of chilled embryos contain certain 

 substances not present in unchilled embryos, which are capable of 

 inducing germination in the latter. It would seem, therefore, that the 

 effect of chilling is not to reduce the level of inhibitor but to increase 

 the level of an endogenous germination stimulator which overcomes 

 the effect of the inhibitor; some evidence in support of this hypothe- 

 sis was obtained in the following experiment. The region of a 

 chromatogram containing the inhibitor (Rf 0.65 to 0.80) was cut into 

 four strips and each strip moistened with one of the following: (1) 

 eluate from Rf 0.2 to 0.3 of a chromatogram of extract of 10 unchilled 

 embryos; (2) eluate from Rf 0.2 to 0.3 of a chromatogram of extract 

 of 10 chilled embryos; (3) distilled water (control); (4) 0.25 per cent 

 thiourea. A further control of filter paper moistened wuth distilled 

 water only was set up (i. e., no inhibitor). Leached (nondormant) 

 embryos were then planted on the paper. It was found that there 

 was little germination either on the paper containing only inhibitor 

 or inhibitor plus extract of unchilled embryos (Table 1) . On the 



Table 1 . Interaction between inhibitor and germina- 

 tion promoter in embryos of F. excelsior. 



* Leached, unchilled embryos weie placed on filter paper 

 moistened with solutions indicated — 20 embryos per dish. 



other hand, the presence of extract from cliillcd embryos enabled 

 the test embryos to overcome the effect of the inhibitor, and thiourea 

 was almost equally effective. Embryos receiving only water produced 

 stunted seedlings, those exposed to the inhibitor did not grow further, 

 while those exposed to the eluate from chilled embryos produced 

 normal seedlings. It would seem, therefore, that the effect of chilling 

 is to lead to the acciunulation of a germination promoter ^vhirli en- 

 ables liie embryo to overcome the effects of the inliiljitor. 



DISCUSSION 



Fxom the foregoing evidence, it would seem that both promoters 

 and inhibitors are involved in the control of dormancy in embryos of 

 /'". excelsior. Although it appears that the changes resulting from chill- 



