The xylem is structurally and fuctionally a complex tissue. It consists of the different types of xylem elements performing the same functions the conduction, storage and support. The tracheids and vessels are lignified with secondary wall thickenings and the protoplasm is absent at maturity. Xylem parenchyma cells helps in the storage and lateral translocation of the solutes. The tracheary elements are the most highly specialized among the xylem cells and it the principal water conducting cells.