Airdried—The dried condition of lumber, usually 12 to 20 percent moisture content, reached by exposing the wood for a sufficient period to the prevailing atmospheric con­ditions.

Air drying—The process of drying green lumber by exposure to prevailing atmospheric conditions.

Annual growth ring—The growth layer added to the tree each year in temperate climates, or each growing season in other climates; each ring includes springwood and summer- wood.

Bark—Outer layer of a tree, which consists of a thin, living inner part and a dry, dead outer part that is generally resistant to moisture movement.

Birds-eye—Small localized areas in wood with the fibers indented and otherwise contorted to form few to many small circular or elliptical figures remotely resembling birds’eyes on the tangential surface. Common in sugar maple and used for decorative purposes; rare in other hardwood species.

Board— (1) Yard lumber that is less than 2 inches (50 mm) thick and 2 or more inches wide. (2) A term usually applied to 1-inch- (25.4-mm-) thick lumber of all widths and lengths.

Broad-leaved trees— (See Hardwoods.)

Cambium—The one-cell-thick layer of tissue between the bark and wood that repeatedly subdivides to form new wood and bark cells.

Canal, resin— (See Resin canal.)

Cell—In wood anatomy, a general term for the minute units of wood structure having dis

tinct cell walls and cell cavities. Includes wood fibers, vessel segments, and other elements of diverse structure and function.

Cellulose—The carbohydrate that is the principal constituent of wood and forms the framework of the wood cells.

Check—Syn: Cracks, drying check, checking. A separation of the wood fibers within or on a log, timber, lumber, or other wood product resulting from tension stresses set up during drying, (usually the early stages of drying).

Clear wood—Wood without knots.

Cross section—Syn: Transverse section. A section of a board or log taken at right angles to the grain.

Cup—A form of board warp in which there is a deviation from a straight line across the width.

Decay—Syn: Rot, dote. The decomposition of wood substance by fungi. In advanced (or typical) decay, destruction is readily recognized because the wood has become punky,

soft and spongy, stringy, ringshaked, pitted, or crumbly. Decided discoloration or bleaching of the rotted wood is often apparent. Early (or incipient) decay refers to the stage at which the decay has not proceeded far enough to soften or otherwise percepti­bly impair the hardness of the wood. Early decay is usually accompanied by a slight discoloration or bleaching of the wood.

Defect—An irregularity or imperfection in a tree, log, bolt, or lumber that reduces its vol­ume or quality or lowers its durability, strength, or utility value. Defects may result from knots and other growth conditions and abnormalities; from insect or fungus at­tack; and from milling, drying, machining, or other processing procedures.

Density—The weight of a body per unit volume, usually expressed in pounds per cubic foot (grams per cubic centimeter). In wood, density changes in terms of moisture con­tent.

Diffuse-porous wood—A hardwood in which the pores tend to be uniform in size and distribution throughout each annual ring or to decrease in size slightly and gradually toward the outer border of the ring.

Discoloration—Syn: Stain. Change in the color of lumber resulting from fungal and chemical stains, weathering, or heat treatment.

Dry kiln—A room, chamber, or tunnel in which the temperature and relative humidity of air circulated through parcels of lumber and veneer govern drying conditions.

Drying—The process of removing moisture from wood to improve its serviceability in use.

Drying or kiln schedule—The prescribed schedule of dry-bulb temperature and wet-bulb temperature or relative humidity used in drying; sometimes expressed in terms of wet- bulb depression or equilibrium moisture content (EMC). In kiln drying, air velocity is an important aspect.

Earlywood—Syn: Springwood. Wood formed during the early period of annual growth; usually less dense and mechanically weaker than wood formed later.

Extractives—Substances in wood, not an integral part of the cellular structure, that can be removed by solution in hot or cold water, ether, benzene, or other solvents that do not react chemically with wood substances.

Fiber, wood—A comparatively long, narrow, tapering hardwood cell closed at both ends. Figure—The pattern produced in a wood surface by annual growth rings, rays, knots, devia

tions from regular grain such as interlocked and wavy grain, and irregular coloration. Flatsawn—Lumber sawed in a plane approximately perpendicular to a radius of the log.

See Grain.

Fungi—Low forms of plants consisting mostly of microscopic threads that traverse wood in all directions, converting the wood to materials the plants use for their own growth. Fungi cause decay and staining of lumber.

Fungicide—A chemical that is toxic to fungi.

Grade—A classification or designation of the quality of manufactured pieces of wood or of logs and trees.

Grain—The direction, size, arrangement, appearance, or quality of the fibers in lumber. When used with qualifying adjectives, the term designates the orientation of fibers and/or growth rings in lumber.

End grain—The ends of wood pieces that are cut perpendicular to the fiber direction. Flat grain—Syn: Flatsawn, plain grain, plainsawn, tangential cut. Lumber sawn or split in a plane approximately perpendicular to the radius of the log. Lumber is consid­ered flatgrained when the annual growth rings make an angle of less than 45' with the surface of the piece.

Straight grain—Lumber in which the fibers and other longitudinal elements run paral­lel to the axis of a piece.

Green lumber—(1) In general, lumber just as cut from freshly felled trees. (2) In accor­dance with the American Softwood Lumber Standard, lumber above 19 percent mois­ture content.

Green volume—Cubic content of green wood.

Growth ring—A layer of wood (as an annual ring) produced during a single period of growth.

Growth rate—The rate at which a tree has laid on wood, measured radially in the tree trunk or in the radial direction in lumber. The unit of measure in use is the number of annual growth rings per inch.

Hardwood—Generally, one of the botanical groups of trees that have broad leaves-—e.g., oak, elm, basswood—in contrast to the conifers or softwoods. Also, the wood pro­duced from such trees. (The term has no reference to the actual hardness of the wood.)

Heartwood—The inner layers of wood in growing trees that have ceased to contain living cells and in which the reserve materials, e.g., starch, have been removed or converted into resinous substances. Heartwood is generally darker than sapwood, although the two are not always clearly differentiated.

Infection—The invasion of wood by fungi or other micro-organisms.

Infestation—The establishment of insects or other animals in wood.

Juvenile wood—The initial wood formed adjacent to the pith, often characterized by lower specific gravity, lower strength, higher longitudinal shrinkage, and different micro­structure than that of mature wood.

Kiln—A chamber or tunnel used for drying and conditioning lumber, veneer, and other
wood products in which the temperature and relative humidity are controlled.

Kiln drying—The process of drying lumber in a closed chamber in which the temperature and relative humidity of the circulated air can be controlled.

Knot—That portion of a branch or limb that has been surrounded by subsequent growth of the wood of the trunk or other portions of the tree. A knot hole is merely a section of the entire knot, its shape depending upon the direction of the cut.

Latewood—Syn: Summerwood. The portion of the annual growth ring that is formed after the earlywood formation has ceased. Latewood is usually denser and mechanically stronger than earlywood.

Lumber—The product of the sawmill and planing mill not further manufactured except by sawing, resawing, passing lengthwise through a standard planing machine, cross cut­ting to length, and matching.

Lumber, boards—Lumber less than 2 inches (50 mm) thick and 2 or more inches wide.

Lumber, dimension—Lumber from 2 inches (50 mm) up to 5 inches (127 mm) thick

and 2 or more inches wide. Includes joists, rafters, studs, planks, and small timbers.

Lumber, timbers—Lumber 5 inches (127 mm) in the smallest dimension. Includes

beams, stringers, posts, caps, sills, girders, and purlins.

Lumen—In wood anatomy, the cell cavity.

Mineral streak—An olive to greenish-black or brown discoloration of undetermined cause in hardwoods, particularly hard maples; commonly associated with bird pecks and other injuries; occurs in streaks usually containing accumulations of mineral matter.

Moisture content, wood—Weight of water contained in the wood, expressed as a per­centage of the weight of the ovendry wood. Moisture content classes:

Airdried—Wood having an average moisture content of 25 percent or lower, with no material over 30 percent.

Green—Freshly sawn wood or wood that essentially has received no formal drying. Kiln dried—Dried in a kiln or by some other refined method to an average moisture content specified or understood to be suitable for a certain use. Kiln-dried lumber can be specified to be free of drying stresses.

Partly airdried—Wood with an average moisture content between 25 and 45 percent, with no material over 50 percent.

Shipping dry—Lumber partially dried to prevent stain or mold in brief periods of tran­sit, preferably with the outer 1/8-inch (3-mm) dried.

Mold—A fungus growth on lumber at or near the surface and, therefore, not typically re­sulting in deep discolorations.

Naval stores—A term applied to the oils, resins, tars, and pitches derived from oleoresin contained in, exuded by, or extracted from trees chiefly of the pine species (genus Pinus) or from the wood of such trees.

Old growth—Timber in or from a mature, naturally established forest. When the trees have grown during most, if not all, of their lives in active competition with other trees for sunlight and moisture, the timber is usually straight and relatively free of knots. Ovendry—The term used to describe wood that has been dried in a ventilated oven at 100oF to 105°F (37°C to 40°C) until there is no further loss in weight.

Pith—The small, soft core at the original center of a tree around which the wood forms. Plainsawn—Another term for flatsawn or flatgrained lumber.

Pore—The cross section of a specialized hardwood cell known as a vessel. See Vessels. Porous woods—Another name for hardwoods, which frequently have vessels or pores large enough to be seen readily without magnification.

Preservative—Any substance that is effective, for a reasonable length of time, in prevent­ing the development and action of wood-rotting fungi, borers of various kinds, and harmful insects that deteriorate wood.

Quartersawn—Another term for edge-grained lumber, showing the radial surface of the wood.

Radial surface—A longitudinal surface or plane extending wholly or in part from the pith to the bark.

Ray—A ribbon-like grouping of cells extending radially across the grain, so oriented that 132        the face of the ribbon is exposed as a fleck on the surface.

Relative humidity—The amount of water vapor in the atmosphere, expressed as a per­centage of the maximum quantity that the atmosphere could hold at a given tempera­ture. The amount of water vapor that can be held in the atmosphere increases with the temperature.

Resin canal (or duct)—An intercellular passage that contains and transmits resinous materials. Resin canals extend vertically or radially in a tree.

Ring, annual growth—See Annual growth ring.

Ring-porous wood—Wood in which the pores of the earlywood (springwood) are dis­tinctly larger than those of the latewood (summerwood) and form a well-defined zone or growth ring.

Rot—Decay.

Sap—The moisture in green wood, containing nutrients and other chemicals in solution.

Sapwood—The outer zone of wood in a tree, next to the bark. In a living tree, sapwood contains some living cells (the heartwood contains none), as well as dead and dying cells. In most species, it is lighter colored than the heartwood. In all species, it lacks resistance to decay.

Season—To dry lumber and other wood items to the desired final moisture content and stress condition for their intended use.

Second growth—Timber that has grown after the removal, whether by cutting, fire, wind, or other agency, of all or a large part of the previous stand.

Shrinkage—The contraction of wood fibers caused by drying below the fiber saturation point. Shrinkage (radial, tangential, and volumetric) is usually expressed as a percent­age of the dimension of the wood when green.

Softwood—Generally, one of the botanical groups of trees that, in most cases, have nee­dlelike to scalelike leaves; the conifers. Also, the wood produced by such trees. (The term has no reference to the actual hardness of the wood.)

Species—A group of individual plants of a particular kind; that is, a group of individuals sharing many of the same characteristics. Species is lower in classification than the genus, but higher than the variety.

Specific gravity—The ratio of the ovendry weight of a piece of wood to the weight of an equal volume of water at 39°F (4°C). Specific gravity of wood is usually based on the green volume and ovendry weight.

Springwood—See Earlywood.

Stain—A discoloration in wood that may be caused by micro-organisms, metal, or chemi­cals. The term also applies to materials used to impart color to wood.

Strength—The term in its broad sense includes all the properties of wood that enable it to resist different forces or loads. In its more restricted sense, strength may apply to any one of the mechanical properties.

Stress—Force per unit of area.

Summerwood—See Latewood.

Swelling—Increase in the dimensions of wood caused by increased moisture content. Swel­ling occurs tangentially, radially, and, to a less extent, longitudinally.

Tangential—Strictly, coincident with a tangent at the circumference of a tree or log, or parallel to such a tangent. In practice, however, tangential often means roughly coinci­dent with a growth ring. A tangential section is a longitudinal section through a tree or limb and is perpendicular to a radius. Flat-grained and plainsawn lumber is sawn tan­gentially.

Tension wood—A type of wood found in leaning trees of some hardwood species, charac­terized by the presence of fibers technically known as “gelatinous” and by excessive longitudinal shrinkage. Tension wood fibers tend to “pull out” on sawn and planed sur­faces, giving so-called fuzzy grain. Tension wood causes crook and bow and may col

lapse. Because of slower than normal drying, tension wood zones may remain wet when the surrounding wood is dry.

Texture—A term often used interchangeably with grain; sometimes used to combine the concepts of density and degree of contrast between springwood and summerwood. In this publication, texture refers to the finer structure of the wood (see Grain) rather than the annual rings.

Tyloses—Masses of cells appearing somewhat like froth in the pores of some hardwoods, notably white oak and black locust. In hardwoods, tyloses are formed when walls of living cells surrounding vessels extend into the vessels. They are sometimes formed in softwoods in a similar manner by the extension of cell walls into axial tracheids.

Vessels—Wood cells in hardwoods of comparatively large diameter that have open ends and are set one above the other so as to form continuous tubes. The openings of the ves­sels on the surface of a piece of wood are usually referred to as pores.

Virgin growth—The original growth of mature trees.

Warp—Distortion in lumber causing departure from its original plane, usually developed during drying. Warp includes cup, bow, crook, twist, and kinks or any combination thereof.

Weathering—The mechanical or chemical disintegration and discoloration of the surface of lumber that is caused by exposure, light, the action of dust and sand carried by winds, and the alternate shrinking and swelling of the surface fibers with continual variation in moisture content brought by changes in the atmosphere. Weathering does not in­clude decay.

Wood—Syn: Xylem. The tissues of the stem, branches, and roots of a woody plant lying between the pith and cambium, serving for water conduction, mechanical strength, and food storage, and characterized by the presence of tracheids or vessels.

Wood, reaction—In wood anatomy, wood with more or less distinctive anatomical char­acteristics; formed in parts of leaning or crooked stems and, branches. Reaction wood consists of tension wood in hardwoods and compression wood in softwoods.

Workability—The degree of ease and smoothness of cut obtainable with hand or machine tools.

Xylem—The tissues of the stem, branches, and roots of a woody plant lying between the pith and cambium, serving for water conduction, mechanical strength, and food stor­age, and characterized by the presence of tracheids or vessels.