The diurnal and seasonal courses of stomatal conductance (g,) of winter wheat in well watered field and clear sky days were investigated.Experiments were conducted in Beijing Da Tun Experiment Station of Agricultural Ecosystems by automatic porometer in 1984. The diurnal course of g, was a double-peak curve .The decrease of g, at midnoon which might be the result of .the high light density and the high water vapour deficit may limit the photosynthetic potential.The ratio of abaxial conductance (gt) to adaxi...