STUDIES ON THE RELATIONSHIP OF LOW TEMPERATURE EXOTHERM AND FREEZING INJURY OF MEI FLOWER, ITS INTERSPECIFIC HYBRIDS AND THEIR PARENTAL SPECIES Effect of Plant Growth Regulators on Potted Cultivation of Mei Flower Effect of Plant Growth Regulators on Potted Cultivation of Mei Flower On the Classifica tion System of Prunus mume Cultivars A New System for Classify ing China Mei Cultivar Groups , with SpecialReference to Developing Super ior ities of Interspecific Hybrid OriginatedGroups On the Classifica tion System of Prunus mume Cultivars A New System for Classify ing China Mei Cultivar Groups , with SpecialReference to Developing Super ior ities of Interspecific Hybrid OriginatedGroups