plant vascular system xylem A complex tissue in the vascular system of higher plants that consists of vessels, tracheids, or both usually together with wood fibers and parenchyma cells, functions chiefly in conduction of water and dissolved minerals but also in support and food storage, and typically constitutes the woody element (as of a plant stem). A portion of vascular tissue (PO:0009015) that has as part one or more tracheary elements (PO:0000290). Functions in the translocation of water and solutes from roots (PO:0009005) to the shoot system (PO:0009006) and in support. Tracheary elements have lignified cell walls with secondary thickening and are dead at maturity. portion of xylem tissue