The outer portion of a woody stem or root is called “bark”. Sometimes it is hard to tell how much of the stem should be called bark. In the palm tree, for example, there is no clear separation between bark and wood.
What does bark do for the tree?
One of its main functions is to protect the inner, more delicate structures. It not only keeps them from drying out but also guards against outside injuries of various sorts.
The thick, fibrous barks of some redwood trees in America show scars as a result of fires near the ground, but the inner portions of the tree escaped injury.
The process by which bark is formed may go on year after year. In the very young branch of a maple, for example, there is no rough bark as such. The surface of the shoot is nearly smooth. As the twig forms more wood and grows in size, the outer portions may split open. The injury caused in this way is healed from the inside.
Some of the outer portions dry and die. The dead, broken portions give the bark a rough appearance. Some of the dry pieces are shed or broken off as the twig grows larger and older.
Man finds the bark of many trees very useful. Commercial cork is obtained almost entirely from the cork oak tree. The bark of the hemlock tree is used in the tanning of leather. The spice we know as cinnamon is the powdered bark of a tree that grows in India and Malaya. Quinine is obtained from the bark of the cinchona tree. Extracts from the bark of other trees are used for flavoring, and the bark of the roots and branches of many trees are used in medicines.