This paper reviews the literature discussing some of the qualities and properties of spruce that characterize its refractory nature and influence its treatability. Topics discussed include a review of the permeability of spruce, fluid flow through wood, and the anatomy of spruce.Permeability and liquid flow through wood are discussed, with an emphasis on differences in flow between sapwood and heartwood and between earlywood and latewood. Literature covering the effects of reversing the direction of flow and decreases in flow with time are also reviewed. Permeability through earlywood and latewood was variable, with neither being more or less treatable than the other. Reversing the direction of flow through wood was shown to increase the rate of flow, which normally tapers off over time.Discussion of wood anatomy and the path of flow includes a review of longitudinal flow and transverse flow. Pit aspiration and the effects of surface tension, the rigidity of pit membrane, and the adhesion of the torus to pit border are also addressed
