Analysis on the Factors Influencing Transformation of Cassava (Manihot esculenta Crantz) Mediated by Agrobacterium tumefaciens Cassava Genetic Transformation and its Application in Breeding EFFECTS OF SEVERAL AUXINS ON SOMATICEMBRYOGENESIS AND PLANT REGENERATION IN CASSAVA Chemical Constituents from the Stems of Cassava (Manihot esculenta) in Hainan