The stele includes the primary vascular tissue, medullary rays, the pericycle and the pith. It occupies the central part of the stem. The stele has number of vascular bundle based on the plant type.
Whereas the vascular bundle consists of three parts; centre of the bundle lies the xylem which is thick walled. And towards the peripheral part of the bundle lies the phloem which is thin walled. The xylem and phloem cells are separated by a meristematic tissue called as the cambium. These all together is known as the vascular bundle.