Wood types differ considerably in properties such as color, density, and hardness, making timber a resource that is valuable in a wide variety of contexts. Each of the samples of commonly used woods shown here has distinctive characteristics. Mahogany is a tropical tree prized for its heavy, strong, easily worked wood. Hickory is a tough, hard wood used for tool handles, furniture, and smoke wood for meat. Instrument makers favor the strong, richly colored wood of the cherry tree. Yew is strong, fine-grained wood used for cabinetmaking and archery bows. Like mahogany, the wood of the iroko is resistant to both rot and insects and bears the "interlocked" grain of many tropical trees. Oak is one of the world's most durable woods. It is used in barrel-making, veneers, and flooring. A rich color and swirling grain makes walnut a popular wood for cabinets and gunstocks. Larch is a tough, relatively cheap wood used in construction and frequently made into pulp for paper.
The typical markings, called grain, that are found on all types of natural wood are due to the structure of the wood. Wood consists essentially of fine cellular ducts or tubes, which carry water and dissolved minerals from the roots to the leaves, and which are thus arranged more or less vertically within the trunk. When the wood is cut parallel to the axis of the trunk, straight-grained lumber is usually produced. In some trees, however, the ducts are helical; that is, they twist around the trunk as they ascend. Such trees produce cross-grained lumber, which is also obtained from ordinary trees when the cut is not parallel to the axis of the trunk.
Many woods have prominent annual rings. The trunk of a tree does not grow in length, except at its tip, but does grow in width. The only portion of the trunk that is engaged in active growth is the cambium, a thin layer entirely surrounding the trunk. In trees of the Temperate Zone, the cambium lays down new wood during the spring and summer, and in...
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