Figure 36.3: Infrared images of the light pulse sequence: a at 20 min: transpi-ration is high, therefore, the leaf is cool. The reference plate is indicated above the leaf; b at 40 min: stomata are nearly closed, leaf temperature is very similar to the reference plate temperature.
The light pulse was given by a slide projector suspended above the cuvette. A filter restricted the incident light to a wavelength of 350–460 nm (blue). This was necessary to reduce the amount of heat put into the leaf by the projector without losing control on stomatal aperture.
36.4 Measurements 775
kleaf heat= 8.84 mm (36.20)
was established for an estimated wind velocity of 1.4 ms−1inside the cuvette. This is compatible with results quoted in Linacre . Due to the design of the cuvette, wind velocities are not known accurately and can not be measured.