Courtesy G. Lumis
This strong mainstay of the tree begins as a tender stem from which leaves begin to sprout. The trunk is the body of the tree, which not only supports the crown, but in addition internally channels sap and tree food from one part of the tree to another.
A tree grows taller by adding new growth at the tip. In the spring, a new shoot starts to grow at the very tip of the tree. This is called the leader. Its length indicates how much a tree has grow over the course of a year. New shoots grow out sideways from the base of the leader. Each end of each branch has a similar growth of shoots. By summers' end, buds form on the new shoots, and from these buds will develop next year's shoots.
The girth of a tree develops in quite a different way. Between the bark and the wood is a thin soft layer called the cambium. Each year this cambium produces a new layer of wood. You cannot see these layers as they are hidden by the bark. However, the age of cut trees may be determined by counting these layers- called annual growth rings - on the stump.