Softwood Structure

A knowledge of the physical nature of softwood xylem is basic to an understanding of wood and wood products. This chapter examines the structural characteristics of softwoods. The great majority of softwood volume is composed of long, slender cells called longitudinal tracheids. Pit aspiration develops more frequently in earlywood (characterized by large pits) than in latewood. A small portion of the volume of some softwoods is composed of longitudinally oriented parenchyma cells. Longitudinal resin canals arise following cell formation in the cambium and are formed through separation at the adjoining corners of several undifferentiated longitudinal cells. Production of resin canals in response to injury or other traumatic events is not restricted to those genera that produce resin canals of the normal type. Uniformly narrow rays characterize softwoods except where horizontal resin canals are present. The cells composing softwood rays may be either ray parenchyma or ray tracheids.