vascular bundle(redirected from Bundle-sheath)
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vascular bundle,in botany, a strand of conducting tissue extending lengthwise through the stems and roots of higher plants, including the ferns, fern allies, gymnosperms, and angiosperms. The vascular bundle consists of xylem, which conducts water and dissolved mineral substances from the soil to the leaves, and phloem, which conducts dissolved foods, especially sugars, from the leaves to the storage tissues of the stem and root. The structure of vascular bundles varies among the different plant groups. See woodwood,
botanically, the xylem tissue that forms the bulk of the stem of a woody plant. Xylem conducts sap upward from the roots to the leaves, stores food in the form of complex carbohydrates, and provides support; it is made up of various types of cells specialized for each of
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in plants, the aggregate of elements of the vascular tissue. The vascular bundle appears in the sprout from the apical meristem or, more precisely, from the procam-bium. It comprises the xylem, the phloem, mechanical tissues, and cells of the living parenchyma. A vascular bundle may be complete or incomplete; that is, in the latter case it may consist of only phloem or only xylem. Dicotyledons are marked by open vascular bundles; in other words, part of the procambium is not differentiated into vascular tissue and remains in the form of cambium. Monocotyledons have closed bundles, without a cambium.
In a collateral bundle, the phloem occurs along one side of the stem, outside the xylem. The presence of phloem along both sides of the xylem makes the bundle bicollateral. A concentric bundle is one that is either amphibasal, with the xylem surrounding the phloem, or amphicribral, with the phloem surrounding the xylem. The structure of a vascular bundle may vary at different points along the stem.
In roots the vascular bundles form radial structures consisting of individual alternating sections of xylem and phloem along the radii of the vascular cylinder.