Secondary growth
Secondary growth is the growth that results from cell division in the cambia, or lateral meristems, and that causes the stems and roots to thicken.
Primary growth is growth that occurs as a result of cell division at the tips of stems and roots, and that gives rise to primary tissue. Secondary growth occurs in most seed plants, but monocots usually lack secondary growth. If they do have secondary growth, it differs from the typical pattern of other seed plants. In many vascular plants,
secondary growth is the result of the activity of the two lateral meristems, the cork cambium and vascular cambium. Arising from
lateral meristems, secondary growth increases the girth of the plant root or stem, rather than its length. As long as the lateral meristems continue to produce new cells, the stem or root will continue to grow in diameter. In woody plants, this process produces wood. Secondary growth results in an increase in diameter. Obstructions, both foreign objects such as this metal post, and parts of the plant, such as stubs of limbs, can be "swallowed" by continued growth.