Study on Exogenous Spermidine Improving Resistance to Powdery Mildew in Melon Seedlings Effects of silicon on earliness and photosynthetic characteristics of melon Studies of Somatic Embryo via Cotyledon Induction in Cucumis melon L.‘Hetao’ Studies of Somatic Embryo via Cotyledon Induction in Cucumis melon L.‘Hetao’ Effects of silicon on earliness and photosynthetic characteristics of melon Study on the Construction of a Vector Expressing Melon ACO1 Antisense Gene and Its Transference to Nicotiana tabacum