104 P. F. Wareing and T. A. Villiers 



A study of dormancy in seeds of Fraxinus excelsior, in relation to 

 growth substances and inhibitors, is reported. In order to remove the 

 dormancy of these seeds, a period of maturation for 4 to 6 weeks at 

 warm temperatures is required, followed by chilling treatment for 

 5 to 6 months. The dry seeds contain no inhibitors, but after they 

 have been permitted to imbibe water for 24 hrs., a water-soluble in- 

 hibitor is present in the endosperm and embryo, and is apparently 

 metabolically produced. The unchilled embryos themselves are dor- 

 mant, but their dormancy can be removed by leaching the excised 

 embryos for 48 hrs. Seedlings derived from leached, unchilled em- 

 bryos show stunted growth. Application of inhibitor to leached em- 

 bryos restores their dormancy. Thus, it appears that dormancy in 

 these seeds is due to the presence of the inhibitor in the endosperm 

 and embryo. 



Chilling treatment results in no appreciable reduction in the level 

 of inhibitor. On the other hand, it is found that extracts of chilled 

 embryos contain a germination promoter which is capable of over- 

 coming the dormancy of unchilled embryos. The promoter is able 

 to overcome the effects of the inhibitor when both substances are 

 added to the germination medium. It appears that dormancy in Frax- 

 inus seed is controlled by interaction between the inhibitor and the 

 promoter, and that chilling results in an increase in the concentration 

 of promoter to a level which overcomes the effect of the inhibitor. 

 The promoter is also effective in removing the stunting of seedlings 

 from unchilled embryos. 



LITERATURE CITED 



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