Meristems are regions of active cell division within a plant. In general there are two types of meristems: apical meristems and lateral meristems. Apical meristems are located at the tip (or apex) of the shoot and the root, as well as at the tips of their branches. These meristems occur in all plants and are responsible for growth in length. By contrast, lateral meristems are found mainly in plants that increase significantly in diameter, such as trees and woody shrubs. Lateral meristems are located along the sides of the stem, root, and their branches; are found just inside the outer layer; and are responsible for growth in diameter.

The term meristem comes from the Greek word meaning "divisible," which emphasizes the fundamental role played by mitotic cell division in these tissues. Meristematic cells are those that divide repeatedly and in a self-perpetuating manner; that is, when a meristematic...