End correction for gaseous diffusion through short capillaries in wood

Summary It is shown that to calculate the rate of gaseous diffusion through an isolated capillary of radius a an end correction of a/2 must be added to the physical length of the capillary. This correction is applicable to diffusion through pit apertures in conifer wood. Mutual interference between diffusion through closely spaced capillaries reduces the end correction. Two approaches to the calculation of this effect are discussed. The pores in many bordered pit membranes are so closely spaced that the end correction becomes negligible. It is shown theoretically that when the end correction is taken into account the tracheid lumen/cell wall pathway provides the path of least resistance for transverse moisture diffusion through conifer wood.