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Describe the structure of the xylem and the phloem.
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The Xylem and Phloem Describe the structure of the xylem and the phloem. Xylem is a vascular tissue that functions in the transport of water and dissolved substances upward in the plant body. It forms a continuous pathway running through the roots, the stem and to the leaves. In the flowering plants, the xylem usually includes two unique types of cells: tracheids and vessel elements. It also includes numerous parenchyma and sclerenchyma cells, especially fibres. The parenchyma cells are the only living cells in the mature, functioning xylem. The cytoplasm and the nuclei of tracheids, vessel elements and sclerenchyma cells disintegrate at maturity, due to the addition of lignin, leaving the thick cell walls. Vessel elements, made from vessel cells, are conductive elements, which are more highly specialised than tracheids. They are characteristic of the flowering plants and do not occur conifers. In general, vessel elements are shorter and wider than tracheids....
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