Chapter 5 - Hardwood Anatomy

Abstract

Hardwoods are identified by the presence of vessels (pores), although a few species lack them. Vessels are the long tubes for conduction of water made up of individual vessel elements attached end to end. Some vessel elements have spiral thickening. This is limited to the elongated tips (ligules) of the vessel elements in sweet gum and black tupelo, and to latewood vessels and vascular tracheids in elm and hackberry. It is rare in tropical species. Ring-porous woods have large-diameter vessels in the earlywood that soon decrease in diameter toward the latewood. Semi-ring-porous woods have a gradual decrease in vessel diameter through the width of the growth ring, with the earlywood vessels of moderately larger diameter than the latewood. Diffuse-porous woods have vessels that do not change much in diameter throughout the growth ring. The diameter of vessels increases with increasing growth ring width and distance from the pith. Tropical woods tend to be diffuse porous. An interesting value for hardwoods would be the parenchyma value by mass (or at least the useful fiber content). This could be obtained by an acid chlorite treatment of wood shavings followed by fiber fractionation. Each fraction should be examined microscopically to determine the efficiency of the separation. This would give an indication of the useful amount of fiber in hardwood.