Theory of Porometers Used in the Study of Stomatal Movements in Leaves

The mathematical theory of porometers, as used by Gregory and his collaborators for the study of stomatal movements in leaves, is given for viscous and diffusive flow of gases. It is shown that under certain conditions the theory applies to both kinds of gas movements; a correction is included for those cases in which the basic assumptions for diffusion are not realized. From determinations of the total leaf resistance to gaseous flow the conductance of the stomata can be found if the mesophyll resistance is known. The importance of this quantity is discussed and demonstrated, methods of measuring it are suggested, and possible checks upon the reliability of the result are described. As an illustration, the theory is applied to some hitherto unpublished data on two pelargonium leaves; the treatment gives results that are internally consistent, and deduced rates of assimilation are found to be of the same order of magnitude as those observed in practice.