Wood Anatomy of Tree Rings

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Wood Anatomy of Tree Rings
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Tree growth begins with photosynthesis to produce
new wood when the growing season begins.
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Trees grow upward and outward (including root
tips), but
tree growth actually begins in the crown and
moves downward due to the growth regulator, auxin.
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Meristems apical and lateral growth
D cell division E cell elongation M cell
maturation
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Meristems annual growth can also be seen in the
branching patterns of many tree species (esp.
conifers)
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When we dissect the trunk, we can see this annual
incremental growth, both upward and outward.
STEM ANALYSIS
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Locally Absent Rings
Rings may be locally absent along the length of
the tree.
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False Ring
Cells leading into the false ring will gradually
decrease in size and then gradually increase back
to earlywood cells.
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Viewing wood tangential, radial, and transverse
planes. We are only interested in which of these?
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Definitions
Cambium the growing (generative) layer between
the xylem and phloem. Xylem principle
strengthening and water conducting tissue of the
stem, roots, and branches. Phloem inner bark,
principal function to distribute manufactured
foodstuffs. Bark dead, outer tissue that
protects the cambium from the external environment
and exposure to pathogens and physical
injury. Vessel the composite, tube-like
structure found in hardwoods from the fusion of
cells in a longitudinal column. Fiber an
elongated cell with pointed ends and a thick or
infrequently thin wall. Rays ribbon-shaped
tissue extending in a radial direction across the
grain of the wood.
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Note the five major portions of the tree trunk.
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Phloem (inner bark)
Cambium
Xylem (wood)
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The Wood Cell 1. Holocellulose a.
alpha-cellulose (40-50) non-soluble
long-chain polymers (glucose) b.
hemicellulose (20-35) readily soluble
short-chain polysaccharides 2. Lignin
(15-35) non-carbohydrate materials in cell
wall, very complex chemical structure. 3.
Numerous Extractives can be removed! a.
tannins b. oils and resins c. other complex
organic compounds
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Cell lumen
Cell wall