Woody plants are plants with very strong and not easily bendable stems such as trees. Woody plants produce wood as a structural tissue. The stems branches and roots are usually covered with a layer of bark. The wood that woody plants produce is a structural cellular adaptation that allows them to survive harsh winters and continue growing instead of dying. This adaptation therefore makes them the largest and tallest terrestrial plants. Wood is primarily composed of xylem cells with cell walls made up of cellulose and lignin. Woody plants form a new layer of woody tissue each year, increasing the diameter of the stem. You can see these tissue layers inside a tree if you were to cut it down. In some monocots such as palms, the wood is formed in bundles that are scattered through the interior of the trunk.