When the actively dividing shoot tips and growing cells of the root of apical meristem begin, the formation of xylem by giving rise to xylems primary. Secondary xylem contains in woody plants expands upto girth and builds a ring around the original primary xylem tissue of the new xylem. After this the primary cells of xylem cells lose their conducting function, forming a harder Skelton that serves support only to the plants and die. Thus, the inner part of the xylem is composed of dead structurally strong primary xylem and on the outer part which secondary xylem serves water transportation and conduction.