Changes in Buds and Seeds in Response to Chilling 



101 



obtained, however, of any increase in auxins active in the Avena 

 coleoptile test as a result of chilling. The discovery of mature gib- 

 berellins in higher plants opens up yet another possibility, since it is 

 well known that gibberellic acid will break the dormancy of potato 

 tubers (21) , of resting-buds of woody species (6) , and of certain seeds 

 (16) . Gibberellic acid was also found to stimulate the germination 

 of dormant, unleached embryos of F. excelsior. 



The possibility that chilling might bring about an increase in 

 growth promoters other than auxins was therefore investigated, dor- 

 mant, unleached embryos of F. excelsior being used as test objects. 

 Aqueous extracts of chilled and unchilled embryos were chromato- 

 graphed, and the dried chromatograms moistened with distilled water. 

 Dormant, unleached embryos were then planted directly onto the dif- 

 ferent sections of the chromatograms. It was found that with the ex- 

 tract of chilled embryos, 8 of 10 embryos germinated within 48 hrs. 

 in the region Rf 0.2 to 0.3, and there was some germination at Rf 

 0.1 to 0.2. No germination occurred with the extracts of unchilled 

 embryos or in the water controls (Figure 5). This germination stimu- 

 lator is present only in the embryo and not in the endosperm of 



^' 2 







UJ 



LJ 



8 - 



6 - 



4 - 











0.4 



0.8 



0.4 



0.8 



Rf 



Fig. 5. Effect of aqueous embryo extracts of Fraxinns excelsior seeds on germina- 

 tion of unchilled embryos. A — extract of unchilled embryos. B — extract of chilled, 

 nongerminating embryos. C — extract of chilled, germinating embryos. Dotted 

 horizontal line indicates water control. 



