secondarygrowth213-page10

secondarygrowth213-page10 - drying characteristics than...

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Secondary Growth in Stems: Wood, Bark and Surface Features - 10 The pattern of rays may also affect wood appearance. Rays that form in clumps may be detectable without magnification, whereas rays that are a single cell wide are visible only microscopically. Another difference in wood appearance is caused by aging of wood. Heartwood contains the older xylem that is non-functioning. Heartwood can rot away, leaving a hollow core, with living tree around it. Heartwood is typically darkened in appearance, caused, in part, by the accumulation of materials. The functioning xylem toward the exterior is the sapwood. Wood density is an important feature in the use of wood commercially as is its specific gravity and moisture content. Wood with uneven growth rings has different
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Unformatted text preview: drying characteristics than wood with more uniform growth. This affects its commercial use. Knots are caused by branches that originated when the stem was younger and subsequently died. Branches formed lower on the stem often die as the tree increases in height. The eventual growth in stem girth surrounds the dead branch, forming a knot. Knots can be tight (if there is a cambium connection between the branch and trunk or loose if there was bark surrounding the branch. Deciduous is another term used with trees. Deciduous refers to a seasonal loss of all of a tree's leaves. Some trees are evergreen, which means that individual leaves are replaced as they die....
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