Apical meristem present on tips of root and stem is responsible for growth in length. Lateral meristem found on the sides take part in increasing girth of plant, e.g. cambium cytologically vascular cambium of root and stem are derived from conjuctive parenchyma and from medullary rays, respectively.Vascular cambium is responsible for secondary growth in dicots with the formation of secondary tissues vascular cambium differ from apical meristem by the presence of vacuole, storage material, thick radial cell wall isodiametric as well as radially elongated cells.