The central stellar region is called central cylinder or vascular cylinder. It consists of pericycle, vascular bundle and pith.
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Pericycle: It is parenchymatous in nature. Pericycle is the layer just inner to the endodermis and is the delimiting layer of vascular bundle. It may be uniseriate or sometimes multiseriate in some other plants. During the secondary growth the pericycle forms the part of the fascicular cambium and forms the complete the cambial ring.
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Vascular bundle: The vascular bundle of the root shows the radial arrangement of xylem and phloem i.e. the xylem element alternate with the phloem element. The xylem is centripetal in development. The xylem elements show exarch arrangement in which the protoxylem points towards periphery and metaxylem points towards the center of the cylinder. The number of vascular bundle may vary from one to many i.e. monarch to polyarch condition.
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Pith: Pith is the central part of the cylinder and is formed of thin parenchymatous cells with intercellular space. In some root the pith maybe absent. In some members tannins cell are also present. The pith is well developed in the monocots.
