Changes ??i Buds and Seeds in Response to Chilling 



97 



substances and inhibitors. Ripe fruits of this species are in a very 

 deep state of dormancy, and neither intact fruits nor seeds will ger- 

 minate over a period of 16 months if they are maintained moist at 

 laboratory temperatures. When the seed is shed, the embryos are 

 morphologically complete, but they need to undergo a further period 

 of maturation, during which there is considerable growth, involving 

 both cell division and cell extension. This maturation takes place 

 more rapidly at laboratory temperatures than at chilling temperatures. 

 The embryos themselves are found to be dormant, when dissected out 

 of the seeds. In order to obtain germination of the intact seeds or 

 fruits, a period of chilling is required, and this is only effective after 

 the embryo has undergone maturation at a higher temperature. The 

 minimum treatment times for the seeds are 1 month at laboratory 

 temperatures, followed by 5 to 6 months of chilling. 



If the dry seed is extracted, first with ether and then with water, 

 then a well-marked growth promoter is found in the ether fraction 

 at Rf 0.8 to 0.9. This is found to be a neutral substance and it ap- 

 pears to be indole-3-acetonitrile (IAN), on the grounds of its Rf value 

 in several solvents and color reactions. This promoter is gradually 

 reduced as the embryo undergoes maturation at laboratory tempera- 

 tures (Figure 1). There is evidence in some extracts (especially of the 

 endosperm) of a second ether-soluble promoter, which may be lAA 

 from its Rf value. 



The aqueous extracts contain certain promoting regions at low 



z 



-I UJ 



< o 



a: ^, 



LJ — ' 



> o 



^ o 



o 



18 - 



16 



14- 



12 



0.4 



0.8 





 Rf 



0.4 



0.8 



Fig. 1. Ether extracts of seeds of Fraxinus excelsior assayed by the Avena coleop- 

 tile test. A — fresh (untreated) seeds; B — seeds imbibed 3 months (embryo full 

 size). Running solvent 99 parts 80 per cent aqueous isopropanol: 1 part ammonium 

 hydroxide (S.G. 0.88); descending chromatography. Solid horizontal line indicates 

 water control. 



