The gaseous permeability of dry Sitka spruce sapwood in the longitudinal and tangential directions has been measured at various mean pressures between 1 and 700 mmHg. From these measurements it has been shown that both the tracheid lumina and the pores in the membranes of the bordered pits make significant contributions to the total resistance to longitudinal fluid flow through the wood, and the number and equivalent radii of the conducting tracheid lumina and the pit membrane pores have been derived. The conducting tracheids have been observed directly by examination of transverse wood sections, after staining the flow-paths with reduced basic fuchsin solution. The conducting tracheids were found mainly in the latewood and their radii and number were in agreement with the values derived from permeability measurements. Direct carbon replicas of bordered pit membranes have been examined in the electron microscope. Unaspirated, i.e. conducting bordered pits were found only in the latewood region and the size and number of the pores in the latewood pit membranes were in agreement with values derived from permeability measurements, which predicted about 250 pit membrane pores of radius 0.14 $\mu $m in series with each conducting tracheid lumen. The effect of a possible distribution of pore size on the results is considered, and the significance of this work in relation to previous work on the gaseous permeability of conifer wood is discussed.