On a New Method for measuring the Stomatal Aperture of Leaves

A method is described of following the behaviour of stomata by utilizing a diffusion phenomenon, the Dufour effect. Hydrogen at laboratory temperature is blown on to one side of the leaf. As it diffuses through the leaf and out the other side it is accompanied by a rapid temperature wave of considerable magnitude. This is picked up by a fine thermocouple near the leaf and passed to a quick period galvanometer. The ‘flick’ of this measures the stomatal conductance. An experiment is described in which the behaviour of a wheat leaf was followed. The results agree well in broad outline with those obtained by other methods. Advantages claimed are that an approximation, at least, is obtained to the value of the important diffusive conductance of the stomata; that the leaf does not have to be enclosed in any way, and that the instrument can easily be made automatic and recording. Ambient temperature changes are not troublesome.