Horticulture Principles and Practices

Outer bark
Inner bark
FIGURE 3–37 Tree bark,
which is comprised of the tissues
outside the cambium, including
the phloem.
Sapwood (light colored)
Heartwood (dark colored)
(a)
(b)
(c)
FIGURE 3–38 Tree bark differs in thickness and roughness. Some are thin and flaky, whereas others are thick and firm. (Source: George Acquaah)
3.7 BARK
As previously stated, the secondary xylem produces wood. The secondary phloem is a
major part of the bark of a tree (Figure 3–37). The bark develops in perennial plants
as the epidermis is replaced by a structure called the periderm. The periderm is composed
of a mixture of cells, some of which are meristematic and are called the phellogen, or
cork cambium. The bark includes the cork cambium and the secondary phloem tissue.
Bark
The part of the stem or
root exterior to the
vascular cambium.
3.7 Bark 87