meristem, a specialized section of plant tissue characterized by cell division and growth. Much of the mature plant's growth is provided by meristems. Apical meristems found at the tips of stems and roots increase the length of these sections. Stems and roots may also grow in thickness or in diameter through cell divisions in lateral, or secondary, meristems, found just under the surface along the length of the stem or root. Tissues derived from differentiated lateral meristem are known as secondary tissues. In one type of lateral meristem, called cambium, or vascular cambium, the cells divide and differentiate to form the conducting tissues of the plant, i.e., the wood, or xylem, and the phloem (see bark; stem). The growth in diameter of tree trunks is wholly dependent on the division of cambium cells. Other meristematic tissues include cork cambium, which divides to produce waterproofing and protective cork tissue at the surface of the stem and root; and intercalary meristems, modified apical meristems found in different positions than either apical or lateral meristems, e.g., in the stem nodes of grasses. See also differentiation, in biology.

In plants, region of cells capable of division and growth. Meristems are classified by location as apical, or primary (at root and shoot tips), lateral, or secondary (in the vascular cambium and cork cambium), or intercalary (at internodes, stem regions between the places at which leaves attach, and at leaf bases, especially in certain monocots, e.g., grasses). Apical meristems give rise to the primary plant body. Lateral meristems provide increase in stem girth. Injured tissues can convert other cells to new meristem for wound healing.

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