Early workers in the fields of plant anatomy and physiology did not believe there were any direct openings between the cells of wood. To explain the movement of viscous organic substances, preserving oils for example, Tiemann (21) advanced the hypothesis that the wood was made permeable by checks which developed in the cell wall during seasoning. Weiss (22) modified this hypothesis to explain why a greater penetration of preserving oils was obtained in the dense summerwood of longleaf pine. Information was later submitted by Bailey (1, 2) which led him to conclude that the intercellular movement of preserving fluids was through small openings in the pit membranes. Scarth (14), after an examination of coniferous wood impregnated with mercury, also concluded that the effective intercellular communication was localized in the bordered pits.Assuming that the pit membrane pores were the means of intertracheid flow, Stamm (15) has used physical methods to obtain the dimensions of the pit perforations. The range in average diameters (of true circles having the same effect as the openings of unknown shape) of the pit perforations in two species was found to be 11 µ to 23 µ. The range in maximum diameters for five woods was found to be 68 µ to 184 µ. Stamm (16) also has recently made determinations of the ratio of the effective capillary length to the effective capillary cross section of the pores in the pit membranes.