TABLE OF CONTENTS By DUANE E.LYON
Wood is the vascular tissue of trees. Woods presently considered to have major commercial value in the United States are obtained from approximately 60 native tree species and over 30 imported species. The varied structure and physical characteristics of these species make wood suitable for a wide variety of products ranging from decorative veneers to utility poles.
Wood is obtained from two classes of trees, commonly referred to as hardwoods and softwoods. The hardwoods are angiosperms and are characterized by broad leaves and seeds enclosed in a fruit. Most hardwoods lose their leaves in the fall or winter. Oak, maple, ash, and walnut are examples of common hardwood trees. The softwoods are members of the gymnosperms classified as conifers. The conifers are characterized by exposed seeds, usually in cones. Typical softwoods include the pines, spruces, and cedars. The terms hardwood and softwood do not indicate the relative hardness of the two types of wood, since many conifers are actually harder than trees of the angiosperm type.
Gross wood structure may be used to differentiate between the hardwood and softwood classes and to identify species within each group. The cross section of a log shows several well-defined features from the outer bark, through the wood, to the central pith. The purpose of the bark is to protect the inner living tissues from injury. The inner portion of the bark is a...
