LEAF TEMPERATURES

Ansari , A. Q., and W. E. Loomis . (Iowa State University, Ames.) Leaf temperatures. Amer. Jour. Bot. 46(10): 713–717. Illus. 1959.—Leaf temperatures were measured with a thermocouple and potentiometer. Readings were taken on leaves of varying thickness, under varying environmental and plant conditions, and during alternating heating and cooling cycles in sun and shade. Leaves tended to assume air temperature. Sunshine heated thin leaves 6–10°C. above the air in about 1 min. Very thick leaves were heated 20°C. above air in 20–30 min. Cooling in still air in shade was at the same rate as heating in sunshine, and the product of this rate times leaf mass in g./cm.² was constant for all leaves tested. Wind at 5 m.p.h. lowered leaf temperature in the sun about half way to air temperature. This cooling effect can result in a reduction of transpiration by wind. Transpiration had a minor effect on leaf temperature. Wilted leaves showed nearly the same temperature response as turgid ones. Dried leaves heated less and cooled faster in shade than transpiring leaves. Vaselined leaves were 1–3°C. warmer than transpiring leaves but showed similar heating and cooling curves.