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Wood
Wood is derived from woody plants, notably trees but also shrubs. Wood from the latter is only produced in small sizes, reducing the diversity of uses. more...
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In its most common meaning, "wood" is the secondary xylem of a woody plant, but this is an approximation only: in the wider sense, wood may refer to other materials and tissues with comparable properties. Wood is a heterogeneous, hygroscopic, cellular and anisotropic material. Wood is composed of fibers of cellulose (40%–50%) and hemicellulose (15%–25%) held together by lignin (15%–30%) .
Uses
Wood has been used for millennia for many purposes, being many things to many people. One of its primary uses is as fuel. It is also used as a material, for making artworks, boats, buildings, furniture, ships, tools, weapons, etc. Wood has been an important construction material since humans began building shelters, and remains in plentiful use today. Construction wood is commonly known as lumber in North America and timber elsewhere. Wood may be broken down and be made into chipboard, engineered wood, hardboard, medium-density fibreboard (MDF), oriented strand board (OSB), paper or used to make other synthetic substances.
Formation
A tree increases in diameter by the formation, between the old wood and the inner bark, of new woody layers which envelop the entire stem, living branches, and roots. Where there are clear seasons, this can happen in a discrete pattern, leading to what is known as growth rings, as can be seen on the end of a log. If these seasons are annual these growth rings are annual rings. Where there is no seasonal difference growth rings are likely to be absent.
Within a growth ring it may be possible to see two parts. The part nearest the center of the tree is more open textured and almost invariably lighter in color than that near the outer portion of the ring. The inner portion is formed early in the season, when growth is comparatively rapid; it is known as early wood or spring wood. The outer portion is the late wood or summer wood, being produced in the summer . In white pines there is not much contrast in the different parts of the ring, and as a result the wood is very uniform in texture and is easy to work. In hard pines, on the other hand, the late wood is very dense and is deep-colored, presenting a very decided contrast to the soft, straw-colored early wood. In ring-porous woods each season's growth is always well defined, because the large pores of the spring abut on the denser tissue of the fall before. In the diffuse-porous woods, the demarcation between rings is not always so clear and in some cases is almost (if not entirely) invisible to the unaided eye.
Read more at Wikipedia.org
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