Transpiration: Its Effects on Plant Leaf Temperature.

A definite and significant temperature gradient exists over the area of a tomato leaflet and is apparently due to the variation in transpiration across the leaflet. Transpiration is most effective at low velocities of air movement, but when the velocity increases, convection becomes the dominant factor. Leaves in which the stomata are allowed to open naturally in response to light attain temperatures about 5 degrees C lower than leaves in which the stomata are forced to remain closed.