Trichomes are hair-like structures on the epidermal surface. ![]() Two cells, known as guard cells, surround each leaf stoma, controlling its opening and closing and thus regulating the uptake of carbon dioxide and the release of oxygen and water vapor. The epidermis of a leaf also contains openings known as stomata, through which the exchange of gases takes place (Figure 5). Epidermal cells are the most numerous and least differentiated of the cells in the epidermis. Woody plants have a tough, waterproof outer layer of cork cells commonly known as bark, which further protects the plant from damage. The dermal tissue of the stem consists primarily of epidermis, a single layer of cells covering and protecting the underlying tissue. Each is distinguished by characteristic cell types that perform specific tasks necessary for the plant’s growth and survival. Like the rest of the plant, the stem has three tissue systems: dermal, vascular, and ground tissue. The cortex, pith, and epidermis are made of parenchyma cells. Which layers of the stem are made of parenchyma cells? MacKenzie credit c: modification of work by Brian Dearth scale-bar data from Matt Russell) (credit a: modification of work by Emmanuel Boutet based on original work by Ryan R. The (c) flax plant is grown and harvested for its fibers, which are used to weave linen, and for its seeds, which are the source of linseed oil. In (b) this drawing, fourteenth-century women prepare linen. ![]() Humans have grown and harvested flax for thousands of years. Inside the cortex is a layer of sclerenchyma cells, which make up the fibers in flax rope and clothing. ![]() The central pith and outer cortex of the (a) flax stem are made up of parenchyma cells. The “strings” of a celery stalk are an example of collenchyma cells.įigure 4. These cells are alive at maturity and are usually found below the epidermis. They provide structural support, mainly to the stem and leaves. Some parenchyma cells also store starch.Ĭollenchyma cells are elongated cells with unevenly thickened walls (Figure 3). Parenchyma cells are responsible for metabolic functions, such as photosynthesis, and they help repair and heal wounds. They are found in the stem, the root, the inside of the leaf, and the pulp of the fruit. Parenchyma cells are the most common plant cells (Figure 2). The stem and other plant organs arise from the ground tissue, and are primarily made up of simple tissues formed from three types of cells: parenchyma, collenchyma, and sclerenchyma cells. Vascular tissue composed of xylem (red) and phloem tissue (green, between the xylem and cortex) surrounds the pith. The central pith (greenish-blue, in the center) and peripheral cortex (narrow zone 3–5 cells thick just inside the epidermis) are composed of parenchyma cells. Stem Anatomyįigure 2. The stem of common St John’s Wort (Hypericum perforatum) is shown in cross section in this light micrograph. The apex (tip) of the shoot contains the apical meristem within the apical bud. An axillary bud is usually found in the axil-the area between the base of a leaf and the stem-where it can give rise to a branch or a flower. The stalk that extends from the stem to the base of the leaf is the petiole. The stem region between two nodes is called an internode. Nodes are points of attachment for leaves, aerial roots, and flowers. Plant stems, whether above or below ground, are characterized by the presence of nodes and internodes (Figure 1). It also helps to transport the products of photosynthesis, namely sugars, from the leaves to the rest of the plant. The stem of the plant connects the roots to the leaves, helping to transport absorbed water and minerals to different parts of the plant. A stem may be unbranched, like that of a palm tree, or it may be highly branched, like that of a magnolia tree. Their main function is to provide support to the plant, holding leaves, flowers and buds in some cases, stems also store food for the plant. Stems may be herbaceous (soft) or woody in nature. Stems are usually above ground, although the stems of some plants, such as the potato, also grow underground. They may range in length from a few millimeters to hundreds of meters, and also vary in diameter, depending on the plant type. Stems are a part of the shoot system of a plant. The leaves just above the nodes arose from axillary buds. The petiole is the stalk connecting the leaf to the stem. ![]() An internode is the stem region between two nodes. Figure 1. Leaves are attached to the plant stem at areas called nodes.
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