Phloem
Phloem, in higher plants, vascular tissue that conducts sugars and other synthesized food materials from the regions of manufacture in the plant to those of consumption and storage. Phloem is found in the vascular bundles, the longitudinal strands of conductive tissue, in association with the water-conducting tissue, or xylem . The vascular bundles constitute major structural units in herbaceous stems and are the veins in leaves. In the vascular cylinder traversing the center of the buttercup root, for example, the xylem forms a star-shaped central core, and bands of phloem are present in the grooves of this core. Typically, the xylem is on the side of the vascular bundle closest to the pith, although other arrangements are not uncommon. In the older portions of a plant the soft cells of the phloem are crushed as new phloem is formed in the growing process and pushed outward. This new phloem is formed by the action of the cambium, or growing zone, a layer of cells that separates the xy...