Plant stem
· Introduction
A stem is one in all 2 main structural axes of a plant, the opposite being the foundation. The stem is generally divided into nodes and internodes:
The nodes hold one or a lot of leaves, as well as buds which can grow into branches (with leaves, conifer cones, or inflorescences (flowers)). Adventitious roots can also be made from the nodes.
The internodes distance one node from another.
The term "shoots" is commonly confused with "stems"; "shoots" usually refers to new contemporary plant growth together with each stems and alternative structures like leaves or flowers. In most plants stems area unit set on top of the soil surface however some plants have underground stems.
· Stem structure
Stem typically include 3 tissues, dermal tissue, ground tissue and vascular tissue. The dermal tissue covers the outer surface of the stem and typically functions to waterproof, protect and control gas exchange. The ground tissue typically consists in the main of parenchyma cells and fills in round the plant tissue. It sometimes functions in photosynthesis. Vascular tissue provides long distance transport and structural support. Most or all ground tissue could also be lost in woody stems. The dermal tissue of aquatic plants stems might lack the waterproofing found in a very
erial stems. The arrangement of the vascular tissues varies wide among plant species.
· Dicot stems
Dicot stems with primary growth have pith within the center, with vascular bundles forming a definite ring visible once the stem is viewed in cross section. The outside of the stem is roofed with associate degree cuticle, that is roofed by a water-resistant cuticle. The cuticle additionally might contain stomata for gas exchange and cellular stem hairs referred to as trichomes. A cortex consisting of layer (collenchyma cells) and endodermis (starch containing cells) is gift on top of the pericycle and vascular bundles.
Woody dicots and plenty of herbaceous dicots have secondary growth originating from their lateral or secondary meristems: the vascular cambium and also the cork cambium or phellogen. The vascular cambium forms between the vascular tissue and bast within the tube bundles and connects to create {a continuous|endless|never-ending|a continual|a n"art-19">The vascular cambium cells divide to supply secondary vascular tissue to the within and secondary bast to the skin. As the stem will increase in diameter because of production of secondary vascular tissue and secondary vascular tissue, the cortex and stratum ar eventually destroyed. Before the cortex is destroyed, a cork cambium develops there. The cork cambium divides to provide waterproof cork cells outwardly and typically phelloderm cells internally. Those 3 tissues kind the periderm, that replaces the cuticle in perform. Areas of loosely blood cell within the periderm that perform in gas exchange ar known as lenticels.
· Monocot stems
Stems of 2 royal palm palms showing characteristic bulge, leaf scars and fibrous roots, Kolkata, India
Vascular bundles area unit gift throughout the flowering plant stem, though targeted towards the surface. This differs from the flowering plant stem that features a ring of tube bundles and infrequently none within the center. The shoot apex in flowering plant stems is a lot of elongated. Leaf sheathes grow up around it, protecting it. This is faithful some extent of just about all monocots. Monocots seldom turn out secondary growth and area unit thus rarely woody, with Palms and Bamboo being notable exceptions. However, several flowering plant stems increase in diameter via abnormal secondary growth.
· Gymnosperm stems
The trunk of this redwood tree is its stem.
Tasmanian tree fern
All gymnosperms are woody plants. Their stems area unit similar in structure to woody dicots except that the majority gymnosperms turn out solely tracheids in their vascular tissue, not the vessels found in dicots. Gymnosperm wood also often contains resin ducts. Woody dicots are called hardwoods, e.g. oak, maple and walnut. In distinction, softwoods area unit gymnosperms, like pine, spruce and fir.
· Fern stems
Most ferns have rhizomes with no vertical stem. The exception is tree ferns, with vertical stems up to concerning twenty metres. The stem anatomy of pteridophytes is a lot of difficult than that of dicots as a result of fern stems typically have one or a lot of leaf gaps in cross section. A leaf gap is wherever the plant tissue branches off to a foliage. In cross section, the plant tissue doesn't kind an entire cylinder wherever a leaf gap happens. Fern stems might have solenosteles or dictyosteles or variations of them. Many nonflowering plant stems have bast tissue on each side of the vascular tissue in cross-sectional.
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