Usually in the higher plants division of labour exists, and due to this, the tissues are arranged in a system called tissue system. The cells are associated in various ways with each other and form tissues. There are three main tissue systems. (1) The dermal or epidermal tissue system, (2) The fundamental or ground, tissue system and (3) The vascular tissue system. The dermal system forms the outer protective covering of the plant and is represented in the primary plant body, by epidermis. Usually in stems which possess the vascular system in the form of solid cylinder, the ground tissue found in between epidermis and vascular cylinder is called cortex. The vascular tissue system consists of a number of vascular bundles which are found to be distributed in the stele.