Fig. 5.3-16. Transverse section of leaf of yucca (Yucca). Yuccas have large, thick leaves that have a tough, leathery texture due to having many bundles of fiber cells. The fiber bundles are recognizable in the high magnification view (below, at the bottom of this page) as consisting of hundreds of fibers located just interior to the epidermis and hypodermis. Because these fibers are not part of the xylem, they are extraxylary fibers. Each of the two big masses of fibers has a lighter region along its inner edge; that region is a bit of phloem and xylem. Because the bundle has both vascular tissue and many fibers, it is a fibrovascular bundle. At the center of the micrograph is another fibrovascular bundle in which the vascular tissue is more abundant: the red cells in the center are xylem conducting cells, the very tiny green cells above the xylem are phloem cells, and above and below the conducting cells are two arc of red fiber cells.

            The low magnification view shows that fibrovascular bundles constitute a large fraction of the leaf’s volume, with the fiber-rich type of fibrovascular bundle being abundant along the leaf’s surface, the conducing cell-rich type of bundle being restricted to the interior of the leaf.