Fig. 7.1-3. Transverse section of leaf of sugar cane (Saccharum officinale). Students often study the xylem of leaf veins (vascular bundles), and this vein in a sugar cane leaf is rather representative of monocots. It is common to encounter a sheath of fibers, which are easy to confuse with tracheary elements because they have thick walls that are usually stained red. But most tracheary elements are much wider than fibers, as are two of the three vessels here. The narrowest vessel is just a little wider than a fiber, and it is often very difficult to be certain if some cells are fibers or tracheary elements.
The set of brownish cells below the two large vessels is the phloem (larger, empty-looking cells are sieve tube members, the small cells with contents are companion cells).