There are two types of vascular tissues, together they for vascular bundles and are responsible for the survival of the plant. Xylem flows only from bottom up to the top and Phloem flows both ways. Phloem is the innermost layer of the bark in most trees. Outer Phloem is dead cells and inner Phloem is living cells, when the primary Xylem cells become dead, losing their conducting function and forming a hard skeleton that serves support to the plant. Xylem is part of a vascular tissue. The vascular tissue transports fluids and nutrients internally. Between the Xylem and Phloem is a meristem called vascular cambium. The tissue divides cells that will become additional Xylem and Phloem cells, as long as the vascular cambium produces new cells, the plant will grow bigger. Xylem is orientated near the adaxial system of the leaf (upper side).
Wilt disease is a disease that can rapidly kill plants. Wilt disease is where the Pathogens invade vascular vessels making the Xylem fail. Wilt disease is prevented by growing resistant varieties, planting disease free materials in well drained and sterilized, fertile soil.