Stomatal dimensions and resistance to diffusion.

In the past, relations of diffusive resistance to stomatal geometry have concerned circular pores or pores that are replaced by equivalent circles of the same area. We calculated the resistance for general shapes that include the realistic slit. The resistance comprises two terms. The first is an outer resistance that depends only on ventilation and leaf geometry and is independent of stomata. The second is an inner resistance and is a function of stomatal interference and of stomatal geometry only. If interstomatal spacing is at least three times stomatal length, interstomatal interference is negligible. The inner resistance can then be calculated by adding the resistance of the two ends and the throat of each stoma. In the case of an elongated stoma, the part of the diffusive resistance per square centimeter determined by stomatal geometry is [Formula: see text] where a, b, d, and n are the semilength, semiwidth, depth, and density of the stomata, and D is the diffusivity. This is the familiar Brown and Escombe result applied to slits.