26 - Softwood Anatomy

Abstract

The characteristics of papermaking fibers depend much upon their anatomy. The pulping characteristics of various fiber sources are dependent upon their species and growing conditions. Most softwood rays are uniseriate unless they contain resin canals; fusiform rays, when present, constitute about 5% of the rays. A few species are biseriate for at least a portion of the ray, but many species can be sporadically biseriate. The height of the ray (number of cells) is a useful tool for softwood identification. The most pronounced feature of softwoods is resin canals in those species which have them. Resin canals are voids surrounded by epithelium cells. Tyloses may occasionally form in the resin canals of heartwood. The pines, spruces, larches, and Douglas—fir genera of Pinaceae contain normal resin canals in the longitudinal and radial directions. The radial canals are part of fusiform rays and are smaller than longitudinal resin canals. The resin canals in pines are particularly large and numerous and occur throughout the growth ring. In the other three genera, they are small, less numerous, appear to be missing from some growth rings, and may be grouped in small, tangential rows.