Abstract:The differentiation of ovule primordium of a hybrid of Phalaenopsis initiated at low temperature (12-18℃) 50 days after pollination, and megasporogenesis appeared 60 days after pollination. The megasporogenesis at normal temperature (20-25℃) was delayed for 10-15 days. Although the megagametophyte formed and even the double fertilization had been finished 70 days after pollination at normal temperature, the megasporogenesis had not yet been finished at low temperature. Nucellar cells degenerated in advance under low temperature, which resulted in thickened embryo sac wall surrounding the megasporocyte. The embryo sac developed into functional megaspores only and no mature embryo sac was generated.