Plant Stem

Let’s know about Plant Stem. A stem is one of the two main structural axes of a vascular plant , the other being the root . It supports leaves, flowers, and fruits, transports water and solutes between roots and shoots in the xylem and phloem, stores nutrients, and produces new living tissue.

Plant Stem
Plant Stem

The stem is generally divided into nodes and internodes:

  • The nodes contain one or more leaves, as well as buds that may develop into branches (with leaves , coniferous cones , or inflorescences (flowers)). Offshore roots can also be produced from bales .
  • Internodes separate one node from another.

The term ” shoot ” is often confused with “stems”; “Shoot” generally refers to new fresh plant growth that includes both the stem and other structures such as leaves or flowers. In most plants the stems are located above the soil surface but some plants have underground stems .

There are four main functions of stems which are as follows:

  • Support and elevation for leaves, flowers and fruits . The stem holds the leaves in the light and provides a place for the plant to store its flowers and fruits.
  • Transport of fluids between roots and twigs in xylem and phloem (see below)
  • Nutrient storage
  • Production of new living tissue. The normal life span of plant cells is one to three years. Stems contain cells called meristems that produce new living tissue every year.

Stems have two pipe-like tissues called xylem and phloem . Xylem tissue transports water by the action of transpiration stretching , capillary action and root pressure . Phloem tissue consists of sieve tubes and their companion cells. The two tissues are separated by the cambium which is a tissue that divides to form xylem or phloem cells.

Special conditions

Climbing stem of Senecio angulatus ., Plant Stem

Stems are often specialized for storage, asexual reproduction, protection or photosynthesis, including the following:

  • Acolescent : Used to describe stems in plants that appear to be stemless. These stems are actually very short, the leaves appear to rise directly above the ground , for example in some Viola species.
  • Arborescent: A tree with woody stems normally with a single stem.
  • Axillary bud : A bud that grows along the stem at the point of attachment of an older leaf. This potentially gives rise to a single shoot.
  • Branched : Aerial stems are described as being branched or non-branched.
  • Bud : An embryonic shoot with an immature stem tip.
  • Bulb : A short vertical underground stem with fleshy storage leaves, such as onions , daffodils , tulips . Bulbs often function in reproduction by dividing to form new bulbs or by producing smaller new bulbs called bulblets. Bulbs are a combination of stem and leaves, so may be better thought of as leaves as the leaves make up the greater part.
  • Caspitose: When the stems grow into tangled masses or clumps or low-growing panicles.
  • Cladode (including phylloclade ): A flattened stem appearing more or less like a leaf and, [2] specialized for photosynthesis, like cactus pads.
  • Climbing : The stem that clings to or wraps around other plants or structures.
  • Corm : A small elongated underground, storage stem, such as taro , crocus , gladiolus .
  • Dembrant: Stem that is flat to the ground and curls up at the ends.
  • Fruticose: Stem that becomes bushy with a woody habit.
  • Herbaceous : Non woody, they die off at the end of the growing season.
  • Internode: The interval between two consecutive nodes. It has the ability to grow either from its base or from its ends, depending on the species.
  • Node: The point of attachment of a leaf or twig on the stem in seed plants . A node is a very small growth area.
  • Stalk: The stems that serve as an individual flower stalk in an inflorescence or infrutescence.
  • Peduncle: A stem that supports the inflorescence.
  • Prick: A pointed extension of the outer layers of the stem, like that of a rose.
  • Pseudostem: A false stem formed from the rolled bases of leaves, which can grow to 2 to 3 m (6 ft 7 in to 9 ft 10 in) tall, like a banana.
  • Rhizome: A horizontal underground stem that functions primarily in reproduction, but also in storage, as in most ferns, iris.
  • Runner: A type of stolon, which grows horizontally above the ground and takes root at the nodes, aiding in reproduction. For example Garden Strawberry, Chlorophytum comosum .
  • Scape: A stem that bears flowers that emerge from the ground and have no normal leaves. Hosta, Lily, Iris, Garlic.
  • Stolon: A horizontal stem that forms near the surface of the ground, producing root plants at its nodes and ends.
  • Thorn: A modified stem with a pointed point.
  • Tuber: A swollen, underground storage stem adapted for storage and reproduction, such as the potato.
  • Woody: Stiff textured stems with secondary xylem.

Stem structure

Plant Stem

The stem usually consists of three tissues, the dermal tissue, the ground tissue, and the vascular tissue. The dermal tissue covers the outer surface of the stem and usually serves to waterproof, protect, and control gas exchange. The ground tissue usually consists mainly of parenchyma cells and fills in around the vascular tissue. It sometimes functions in photosynthesis. Vascular tissue provides long-distance transport and structural support. Most or all of the ground tissue in woody stems may be destroyed. The dermal tissue of the stems of aquatic plants may lack the waterproofing found in aerial stems. The arrangement of vascular tissues varies widely among plant species.

dicot stem

Dicot stems with primary growth in the medulla center, with vascular bundles forming a distinctive ring visible when the stem is viewed in cross-section. The outer part of the stem is covered with an epidermis, which is covered with a waterproof cuticle. The epidermis may also contain stomata for gas exchange and multicellular stem hairs called trichomes. A cortex consisting of the hypodermis (collenchyma cells) and endodermis (starch-containing cells) is present above the pericycle and vascular bundles.

Woody dicots and many nonwoody dicots have secondary growth arising from their lateral or secondary meristem: the vascular cambium and the cork cambium or phylogeny. The vascular cambium forms between the xylem and phloem in vascular bundles and joins to form a continuous cylinder. Vascular cambium cells divide to produce the secondary xylem from the inside and the secondary phloem on the outside. As the stem grows in diameter due to the production of secondary xylem and secondary phloem, the cortex and epidermis are eventually destroyed. Before the cortex is destroyed, a cork cambium develops there. The cork cambium divides externally to produce waterproof cork cells and sometimes internally to phylloderm cells. Those three tissues make up the periderm, Which in function replace the epidermis. Areas of loosely packed cells in the periderm that function in gas exchange are called lenticels.

Secondary xylem is as important commercially as wood. Seasonal variation in growth from the vascular cambium forms annual tree rings in temperate climates. Tree rings are the basis of dendrochronology, which dates wooden objects and related artifacts. Dendroclimatology is the use of tree rings as a record of past climates. The aerial trunk of an adult tree is called the trunk. The dead, deep inner wood of the stem, usually of a larger diameter, is called heartwood and is the result of tylosis. The outer, living wood is called sapwood.

Monocot stem

Vascular bundles are present throughout the monocot stem, although concentrated outward. It differs from dicot stems in having a ring of vascular bundles and often none in the center. The shoot apex is longer in monocotyledonous stems. Protecting it, a leaf sheath grows around it. This is true to some extent in almost all monocots. Monocots rarely produce secondary growth and are therefore rarely woody, palm and bamboo being notable exceptions. However, many monocotyledons increase in diameter through asymmetric secondary growth.

Gymnosperm stems

All gymnosperms are woody plants. Their stems are similar in structure to woody dicots, except that most gymnosperms produce only tracheids in their xylem, and not the vessels found in dicots. The wood of gymnosperms also often contains resinous tubules. Woody dicots are called hardwoods, such as oak, maple and walnut. In contrast, softwoods are gymnosperms, such as pine, spruce and fir.

  • The trunk of this redwood tree is its trunk.
  • Tasmanian Tree Fern

Fern stems

Most ferns have rhizomes with no vertical stem. The exception is the tree fern, which has vertical stems up to about 20 m. The stem anatomy of ferns is more complex than that of dicots because fern stems often have one or more leaf gaps in cross section. A leaf gap is where vascular tissue branches off to a frond. In cross section, the vascular tissue does not form a complete cylinder where a leaf gap occurs. The stems of ferns may be solenostele or dictyostele or variations of them. The stems of many ferns have phloem tissue in cross-section on both sides of the xylem.

Relationship to xenobiotics

Foreign chemicals such as air pollutants, [3] herbicides and pesticides can damage stem structures.

Economic importance

There are thousands of species whose stems have economic uses. The stem provides some of the major staple crops like potato and taro. Sugarcane stems are a major source of sugar. Maple sugar is obtained from the trunks of the maple tree. Vegetables stems from are asparagus, bamboo shoots, cactus pads or nopalitos, kohlrabi, and water chestnut. The spice, cinnamon is the bark of the trunk of a tree. Gum arabic is an important food additive obtained from the trunks of Acacia Senegalese trees. The main ingredient in chewing gum is chile, obtained from the twigs of the chikoo tree.

Medicines derived from stems include quinine from the bark of the cinchona tree, camphor distilled from the wood of a tree in the same genus that provides cinnamon, and curare from the bark of tropical vines to relax muscles.

Wood is used in thousands of ways, such as buildings, furniture, boats, airplanes, wagons, car parts, musical instruments, sports equipment, railroad ties, utility poles, fence posts, piling, toothpicks, matches, plywood, coffins. , shingles, barrels, stairs, toys, tool handles, picture frames, veneer, charcoal and firewood. Wood pulp is widely used to make paper, paperboard, cellulose sponge, cellophane and some important plastics and textiles, such as cellulose acetate and rayon. Bamboo stems also have hundreds of uses, including paper, building, furniture, boats, musical instruments, fishing poles, water pipes, plant parts and scaffolding. The stems of palm trees and tree ferns are often used for the manufacture. Reed stems are an important building material for use in thatching in some areas.

The tannins used to reduce leather are derived from the wood of some trees, such as quebracho. Cork is obtained from the bark of the oak. Rubber is obtained from the trunks of Hevea brasiliensis Rattan, used for furniture and baskets, is made from the palm stems of the tropical vine. Bast fibers for textiles and rope are obtained from stems which include flax, hemp, jute and ramie. The earliest paper was obtained from papyrus stems by the ancient Egyptians.

Amber is the fossilized sap from tree trunks; It is used for jewelry and may contain ancient animals. Coniferous wood resins are used for the production of turpentine and rosin. Tree bark is often used as mulch and in growing media for container plants. It can also become the natural habitat of lichens.

Some ornamental plants are grown primarily for their attractive stems, such as:

  • paper birch bark
  • Twisted branches of corkscrew willow and Harry Lauder’s wand ( Corylus avellana ‘Contorta’)
  • red, peeling bark of a paperbark maple