Plants have two transport tissues, xylem and phloem, together called vascular tissue. They are found grouped into vascular bundles.Xylem transports water and mineral ions from the roots up to the leaves. Transport is in one direction only, upwards. Mature xylem vessels are dead, hollow tubes with walls strengthened by lignin, so xylem also supports the plant.Phloem transports organic substances made by the plant, mainly sucrose and amino acids (assimilates). These move from a source, where they are made or released, to a sink, where they are used or stored. Because sources and sinks can be above or below each other, phloem can move substances in both directions. This movement is called translocation. Phloem is made of living cells.The arrangement of the vascular tissue differs between organs: