Page 22 - Forest Trees of Maine

T P  F

A tree has three major parts: roots, trunk and crown.

Large roots anchor the tree and store foods which are manufactured in the
leaves. Small roots and root hairs absorb water and dissolved mineral salts from the
soil.These raw materials are conducted upward to the leaves where they are utilized
in the synthesis of necessary plant food. Air must be present in the soil for the roots
to live, although some species can endure several months of flooding.
The trunk is the main body of the tree. In the center of the trunk is the pith.
Next to the pith is the heartwood which is composed of dead cells and serves as
support. On the outer side of the heartwood is the sapwood, which contains the
sap conducting tubes. Sapwood is usually lighter in color, but it darkens with age
and becomes heartwood. Heartwood and sapwood together comprise the xylem.
Outside the sapwood is the cambium, a thin layer of cells, which annually produces
new sapwood inwardly and new inner bark outwardly. The cambium produces
diameter growth, and callus growth around open wounds. The inner bark or
phloem is outside the cambium and carries food from the leaves downward to
nourish the cambium and growing parts. The outer bark is the outer-most part of
the tree. Essentially, it is composed of dead cork cells and protects the inner bark
from mechanical injury, drying or disease; it also insulates the phloem from
extremes of heat and cold. Damage to the phloem causes interference with food
movement to growing parts below the injury. Girdling of a tree through its inner
bark will kill the tree.Wood or medullary rays radiate out from the center, and serve
in lateral conduction and as food storage areas. They are most conspicuous in a
cross-sectional view.
The crown is composed of branches, twigs, buds, leaves, flowers and fruit.
The process of photosynthesis occurs in the leaves. Using energy produced by
sunlight, the leaves combine carbon dioxide from the air and water from the soil
to produce carbohydrates. Oxygen is released in the process. Carbohydrates plus
fats and proteins are the plant foods necessary for growth and respiration of the
tree. Flowers and fruit are important in reproduction.

ANNUAL RINGS

The yearly growth of a tree can be compared to the annual placement of hol-
low wooden cones, one on top of the other. Each cone would represent a single
year’s growth over the entire stem. At the beginning of each new growth period,
new wood cells are large and thin-walled, and form the springwood or early wood.
As the growing season progresses, the smaller, thicker-walled cells of the summer-
wood or late wood are produced.The darker appearance of the late wood delineates
the annual ring of growth put on by a tree. The age of a tree, at any desired point
along the trunk, can be determined by counting these annual rings.

20 TR E E P AR TS AND F UNCT IONS