Abstract:In the majority of cases,the dormancy of fruits of manchurian ash (Fraxinus mandshurica Rupr.)may be broken by the treatment of combination of warm and cold stratification,i.e.treatments of warm temperatures (20℃) for 4—5 months and then followed by cold temperatures (5℃) for 4—5 months.There are a number of causes in relation to the dormancy of these seeds,but the main ones are the incomplete development of the embryos and the restriction of the oxygen supply to the embryos by the enveloping layers of the endosperm,testa and pericarp.The action of the growth-inhibitiog substances in the pericarps may also take a part in this respect.At warm temperatures,the embryo undergoes rapidly growth within the imbibed fruit.The roles of low temperaturs are the increase of the intensity of anaerobic respiration of the embryos under oxygen deficient condition,decrease the requirement of oxygen for germination and the increase of the resistant force of the embryos to the action of inhibiting substances.Under the above indicated actions of warm and cold temperatures,the activity of the embryos are able to overcome the resistance of the enveloping membranes and ultimately the seeds germinate.