Winter Injury Index and Lethal Low Temperature for Introducted AmericanAlmond in Lanzhou, China Comparison of Cold Tolerance Within 6 Cultivars of Iris germanica Influence of Chlorophyll Fluorescence Characteristics on Alfalfa Seedlings under Cryogenic Stress THE ECONOMIC THRESHOLD AND FORECAST OF THE LARCH NEEDLE BROWN RUST Comparison of Cold Tolerance Within 6 Cultivars of Iris germanica