countryside. You can climb trees, build a play house
in their branches, picnic in their cooling shade, or just
enjoy walking among them. But trees are valued not
only for their beauty; they are an essential part of our
natural environment, and provide mankind with an important
We all know that a tree has a trunk, branches, leaves,
and roots. But what’s inside a tree? Let’s take a look.
The main building blocks of trees are cellulose fi bers.
Measuring between about 1/32 - 1/4 inch in length
(depending upon the species of tree), these fi bers are
held together in parallel formation with a natural “glue” called lignin. Other natural chemicals, such as sugars,
resins, and oils, are also contained within a tree.
Surprisingly, almost all of the material in a tree is nonliving. Only the leaves, the tips of the branches and roots,
and a thin layer of cells just under the bark are actually
alive. When a tree grows taller, the growth takes place
only at the tips of the stems. For this reason, the birdhouse you’ve mounted on the trunk of a tree will always
remain at the same height, and the swing you’ve hung
from a lower limb will never grow too high to reach!
Trees grow in diameter, too, by the division of cells in the outermost layer. Called the cambium, this microscopic
layer is only three to four cells wide! As cells in the
cambium divide, the old outer bark splits, and cracks
develop in the surface of the tree, giving bark its rough