xylem


xylem

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Cross section of oak xylem—J.M. Langham

Part of a plant's vascular system that conveys water and dissolved minerals from the roots to the rest of the plant and furnishes mechanical support. Xylem constitutes the major part of a mature woody stem or root and the wood of a tree, and consists of specialized water-conducting tissues made up mostly of several types of narrow, elongate, hollow cells. Xylem formation begins when the actively dividing cells of growing root and shoot tips give rise to primary xylem. Eventually the primary xylem is covered by secondary xylem produced by the cambium. The primary xylem cells die, forming a hard skeleton that supports the plant but loses its conducting function. Thus, only the outer part of the wood (secondary xylem) serves in water conduction.

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