Delphinidin

Most monocots (e.g., grasses, lilies) are herbaceous plants that do not attain great size. The stems have neither a vascular cambium nor a cork cambium and thus produce no secondary vascular tissues or cork. As in herbaceous dicots, the surfaces of the stems are covered by an epidermis, but the xylem and phloem tissues produced by the procambium appear in cross section as discrete vascular bundles scattered throughout the stem instead of being arranged in a ring.

Each bundle, regardless of its specific location, is oriented so that its xylem is closer to the center of the stem and its phloem is closer to the surface. In a typical monocot such as corn, a bundle’s xylem usually contains two large vessels with several small vessels between them. The first-formed xylem cells usually stretch and collapse under the stresses of early growth and leave an irregularly shaped air space toward the base of the bundle; the remnants of a vessel are often present in this air space. The phloem consists entirely of sieve tubes and companion cells, and the entire bundle is surrounded by a sheath of thicker-walled sclerenchyma cells. The parenchyma tissue between the vascular bundles is not separated into cortex and pith in monocots, although its function and appearance are the same as those of the parenchyma cells in cortex and pith. In a corn stem, there are more bundles just beneath the surface than there are toward the center. Also, a band of sclerenchyma cells, usually two or three cells thick, develops immediately beneath the epidermis, and parenchyma cells in the area develop thicker walls as the stem matures.

The concentration of bundles, combined with the band of sclerenchyma cells beneath the epidermis and the thickerwalled parenchyma cells, all contribute to giving the stem the capacity to withstand stresses resulting from summer storms and the weight of the leaves and the ears of corn as they mature.

In wheat, rice, barley, oats, rye, and other grasses, there is an intercalary meristem at the base of each internode; like the apical meristem, it contributes to increasing stem length. Although the stems of such plants elongate rapidly during the growing season, growth is columnar (i.e., there is little difference in diameter between the top and the bottom) because there is no vascular cambium producing tissues that would add to the girth of the stems. Palm trees, which differ from most monocots in that they often grow quite large, do so primarily as a result of their parenchyma cells continuing to divide and enlarge without a true cambium developing. Several popular house plants (e.g., ti plants, Dracaena, Sansevieria) are monocots in which a secondary meristem develops as a cylinder that extends throughout the stem. Unlike the vascular cambium of dicots and conifers, this secondary meristem produces only parenchyma cells to the outside and secondary vascular bundles to the inside.

Several commercially important cordage fibers (e.g., broomcorn, Mauritius and Manila hemps, sisal) come from the stems and leaves of monocots, but the individual cells are not separated from one another by retting (a process that utilizes the rotting power of microorganisms thriving under moist conditions to break down the thin-walled parenchyma cells) as they are when fibers from dicots are obtained. Instead, during commercial preparation, entire vascular bundles are scraped free of the surrounding parenchyma cells by hand; the individual bundles then serve as unit "fibers." If such fibers are treated with chemicals or bleached, the cementing middle lamella between the cells breaks down. Monocot fibers are not as strong or as durable as most dicot fibers.