Introduction to Stem:
A stem is one of two major structural axes of the vascular plant. The stem is generally classified into nodes and internodes, the nodes hold buds that grow up into one or more leaves, flowers (inflorescences), cones or other stems and so on. The internodes act as spaces which distance one node from the other. The word shoots is a lot confused by stems; shoots usually refer to new fresh plant growth and does comprise stems however as well to other structures such as flowers or leaves. In many plants stems are positioned above the soil surface however a few plants encompass underground stems.
Major functions of stems:
1) Support for and the elevation of flowers, leaves and fruits. The stems maintain the leaves in the light and give a place for the plant to keep its fruits and flowers.
2) Storage of nutrients.
3) Transport of fluids among the roots and the shoots in the xylem and phloem.
4) The production of new living tissue. The normal life-time of plant cells is one to three years. Stems have cells termed as meristems which annually produce new living cells.
Stem generally comprise of three tissues, dermal tissue, ground tissue and the vascular tissue. The dermal tissue covers the external surface of the stem and generally functions to water-proof, protect and control the gas exchange. The ground tissue generally comprises mainly of parenchyma cells and fills in about the vascular tissue. It at times functions in photosynthesis. Vascular tissue gives long distance transport and structural support.
Mostly all ground tissue might be lost in the woody stems. The dermal tissue of aquatic plants stems might lack the water-proofing found in the aerial stems. The arrangement of the vascular tissues differs broadly among the plant species.
Dicot stems having primary growth have pith in the center, having vascular bundles making a distinct ring visible if the stem is viewed in cross-section. The outside of the stem is covered by an epidermis that is covered through a water-proof cuticle. The epidermis as well might have stomata for gas exchange and hairs. A cortex of parenchyma cells lies among the epidermis and vascular bundles.
Woody dicots and mostly non-woody dicots have secondary growth originating from the lateral or secondary meristems: the vascular cambium and the cork cambium or phellogen. The vascular cambium forms among the xylem and phloem in the vascular bundles and joins to form a continuous cylinder. The vascular cambium cells split to produce secondary xylem to the inside and secondary phloem to the outside. As the stem rises in diameter due to the production of secondary xylem and secondary phloem, the cortex and epidermis are finally destroyed. Before the cortex is destroyed, a cork cambium builds up there. The cork cambium splits to produce water-proof cork cells externally and at times phelloderm cells internally. Such three tissues form the periderm that replaces the epidermis in function. Areas of loosely-packed cells in the periderm that function in gas exchange are termed as lenticels.
The entire gymnosperms are woody plants. Their stems are similar in structure to woody dicots apart from that most gymnosperms generate only tracheids in their xylem, not the vessels found the in dicots. Gymnosperm wood as well frequently includes resin ducts. Woody dicots are termed as hardwoods, example: Oak, Iroko Mahogany, Teak and Walnut. In disparity, softwoods are gymnosperms, like pine, spruce and fir.
Economic significance of Stems:
There are numerous species whose stems encompass economic uses. Stems give a few main staple crops like taro and potato. Sugarcane stems are a main source of sugar. The spice, cinnamon is bark from the tree trunk. Cellulose from tree trunks is a food additive in grated Parmesan cheese, bread and other processed foods. Gum Arabic is a significant food additive get from the trunks of Acacia Senegal trees. Chicle, the major ingredient in chewing gum, is acquired from trunks of the chicle tree.
Medicines get from stems comprise quinine from the bark of Cinchona trees, Camphor distilled from the wood of a tree in the similar genus which gives cinnamon and the muscle relaxant curare from the bark of tropical vines.
Wood is employed in thousands of manners, example: furniture, buildings, boats, airplanes, car parts, wagons, musical instruments, sports equipment, utility poles, railroad ties, fence posts, toothpicks, matches, plywood, coffins, toys, tool handles, charcoal and fire-wood. Wood pulp is broadly employed to make paper, card-board and some significant plastics and textiles, like cellulose acetate and rayon.
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