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Horticulture Principles and Practices

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Outer bark<br />

Inner bark<br />

FIGURE 3–37 Tree bark,<br />

which is comprised of the tissues<br />

outside the cambium, including<br />

the phloem.<br />

Sapwood (light colored)<br />

Heartwood (dark colored)<br />

(a)<br />

(b)<br />

(c)<br />

FIGURE 3–38 Tree bark differs in thickness <strong>and</strong> roughness. Some are thin <strong>and</strong> flaky, whereas others are thick <strong>and</strong> firm. (Source: George Acquaah)<br />

3.7 BARK<br />

As previously stated, the secondary xylem produces wood. The secondary phloem is a<br />

major part of the bark of a tree (Figure 3–37). The bark develops in perennial plants<br />

as the epidermis is replaced by a structure called the periderm. The periderm is composed<br />

of a mixture of cells, some of which are meristematic <strong>and</strong> are called the phellogen, or<br />

cork cambium. The bark includes the cork cambium <strong>and</strong> the secondary phloem tissue.<br />

Bark<br />

The part of the stem or<br />

root exterior to the<br />

vascular cambium.<br />

3.7 Bark 87

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