Effects of temperature and photoperiod on sex differentiation and physiology in Luffa ( luffa acutangula) ⅰ. effects of temperature and photoperiod on sex differentiation and oxidase activities and isoenzyme in Luffa 温度和光周期与丝瓜花性分化及其生理的研究Ⅰ.温度和光周期对丝瓜花性分化和氧化酶活性及其同工酶的影响