A physical mathematical model of water transportation in the soil-plant-atmosphere continuum have been developed recently. To predict daily actual transpiration，much more detailed studies on the behavior of stomata are needed. To make a behavior model of stomatal resistance，concurrent measurements of irradiance，leaf water potential，air temperature，leaf temperature，net radiation，CO₂ concentration， humidity， wind speed and stomatal resistance were obtained in cucumbers under wet soil conditions. The same measurements were made in soybeans under dry and wet conditions. The results indicated that light is likely to have an important role on stomatal behavior under any soil water status. The relationship between stomatal resistance and light fits a hyperbolic curve as shown in Fig. 2. But the duirnal change in leaf water potential did not measurably affect stomatal resistance
