Embryo Immaturity and Dormancy of Black Ash1

Abstract

Abstract The seed of black ash, Fraxinus nigra Marsh., borne in a single samara, normally ripens in the autumn. At that time the seed contains an embryo which is both immature and dormant. In order to overcome this dual delay to germination, the seed can be matured in moist peat moss for 18 weeks at 21° followed by after-ripening for 18 weeks at 4°. Treatment at warm temperature matured the embryo, whereas the subsequent cool temperature after-ripened the dormant embryo. During maturation the embryo length doubled, the dry weight tripled and the cotyledons showed visual evidence of differentiation. On the other hand, for dormancy to be overcome a metabolic shift in the embryo occurred during the cool period to provide the active metabolism needed by a germinating seed. This was reflected by a 5 percent per week increase in the respiration capacity of the embryo and a reduction in the amount of oil in the seed.