The cortex is crushed by the expansion of the woody layer of the stem. Phloem The outside layer of vascular tissue in woody plants is the phloem. It function is to transport food from one part of the plant to another. Companion cells are living, and they have nuclei. Vascular Cambium Between the phloem and the xylem is a narrow layer of cells called the vascular cambium.
Cellular division adds cells to the inside of the phloem and the outside of the xylem.
An increase in the girth of the stem results from this division. Xylem Xylem or wood makes up the bulk of a woody stem. In primitive groups, the xylem consists of only tracheids. In more advanced taxa, more specialized cells for support, called fiber, and much shorter conductive cells called vessels are also found in the xylem. Band of parenchyma run at right angles to the length of the stem.