Study on cold resistance of top buds of Paulownia elongata's seedlings

Top buds，first pair of lateral buds and shoots of one-year-aged seedlings of Paulownia elongata are treated under different low temperatures，and then their electrical conductivity and electrolyte rates are determined．The order of electrical permeation rate is top buds> lateral buds> shoots in the same temperature，the order of lethal temperature is top buds>lateral buds and shoots．Lethal temperature of top bud is -10℃ within 96h．the lateral bud and the shoot within 120h．Lethal temperature of top bud is-15℃ within 72h，the lateral bud and the shoot within 96h．In the natural condition，the temperature does not occur on trial spot in some years，but the top buds die．The reasons are studied in this paper.