Xylem
Xylem, woody tissue, found in higher plants, that conducts water and inorganic salts throughout the plant and provides it with mechanical support. In leaves, flowers, and young stems, xylem is present in conjunction with phloem in the form of conducting strands called vascular bundles. In roots there is a central core of xylem (see Root ). Xylem that derives from the shoot and root-growing points is called primary xylem. In addition, new xylem, called secondary xylem, may be added by the activity of the cambium, which actively divides cells situated between the xylem and phloem. This division gives rise to new xylem cells toward the center in roots and toward the outside in most stems. Some plants have little or no secondary xylem, in contrast to woody plants in which indefinite amounts of secondary xylem is the botanical term equivalent to wood. See Stem . Xylem may contain three types of elongated cells: tracheids, vessel elements, and fibers. At maturity, when functioning in conduc...