Slide 1

PowerPoint® Presentation

Unit 3
The Nature of Wood
Structure of Wood • Cambium •
Sapwood • Heartwood • Moisture
Content of Wood • Effects of
Moisture Content


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Unit 3 — The Nature of Wood

Wood is composed of
tiny cells that are held
together with a natural
cement called lignin.
(The cells are drawn here
many times larger than
their actual size.) Trees
grow by forming new
wood cells, and reach full
maturity and stop
growing when new cells
stop forming.


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Unit 3 — The Nature of Wood

Annual rings begin at
the center of the trunk
and continue outward
to the bark. Each ring
represents a year of
cellular growth.


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Unit 3 — The Nature of Wood

The moisture content of wood is the percentage of its
weight that is water. The oven-drying method
provides an accurate measure of moisture content.


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Unit 3 — The Nature of Wood

A moisture meter is a convenient tool to use to
check the moisture content of wood.


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Unit 3 — The Nature of Wood

Most lumber shrinkage
occurs across the
grain. For example, a
2″ × 4″ × 8′ piece of
lumber will shrink more
across its 2″ thickness
and 4″ width than
along its 8′ length.