Transpiration and Leaf Temperature in Eastern Cottonwood

In summer at midday in central Mississippi, juvenile plants transpiring 10 to 16 X 10 -6 g/cm²/sec had leaves cooler than surrounding air. Leaves transpiring less than 4 X 10 -6 g/cm²/sec were warmer than the surrounding air. Degree of transpiration cooling was negatively correlated with internal water deficit. Leaf diffusion resistances computed from transpiration and temperature data were less than 1.0 sec/cm for freely transpiring plants and from 20.0 to 40.0 for plants under severe moisture stress.