Trees are primarily made up of wood, a special organic material that is a combination of cellulose and lignin. Cellulose is the primary building block of the wood fibers, while lignin holds the cellulose together to form strong structural support for the growing tree.Continue Reading
Wood in trees is formed from a tissue found within all plants, called xylem. Xylem is vascular tissue that circulates water from the roots up through the main body of the plant. Primary xylem grows upward, while secondary xylem grows outward. Wood is formed from the secondary xylem, producing the familiar concentric bands known as tree rings when a tree trunk is cut open.
Young wood is active in transporting water, but wood from previous years is not. This young wood, called sapwood, is still alive. The inner layers of wood are called heartwood. They are dead, and do not play a role in transporting water, although they are still considered part of the xylem. Instead, heartwood tissue remains in place to hold the tree high up above the ground and seek sunlight. Heartwood is strong and able to support heavy masses of branches and leaves, many times what a plant lacking wood would be able to do.Learn more about Trees & Bushes