Monocots are mostly annuals, meaning they live for only a single season. They are most readily recognized by their leaves; although there are exceptions, most monocot leaves exhibit parallel venation. A cross section of a monocot stem (figure 32-13) shows vascular bundles scattered in parenchyma. There may be a layer of sclerenchyma beneath the epidermis.
# Notes £ Although this arrangement of vascular bundles represents the simplest organization of stem structures, it is believed to have evolved comparatively recently Examination of the xylem portion of the vascular bundle reveals two (or perhaps three) large vessels surrounded by small, thick-walled tracheids, see figure 32-14. In addition to the vessels, there is commonly another open space sometimes mistaken for a vessel but lacking a cell wall. This space is produced by a fracture; it is not a cell and is not involved in conduction. The phloem portion of the bundle shows sieve-tube elements with companion cells beside them. The entire bundle is surrounded by a bundle sheath of sclerenchyma. Outside the sheath is the parenchyma, consisting of large, thin-walled cells.
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