What kind of stems are there

Runner develops from the axils of lower leaves of aerial stem which sends slender horizontal branches in the form of runners. When older parts of plant die, the branches separate from parent plant and form independent plants e. Doob grass. It is a slender lateral branch which appears from the lower part of main axis. This lateral branch grows aerially for some distance and becomes arched and finally touches the ground to give rise to new shoot with the help of its terminal bud. It also bears roots to get fixed with the soil e.

Offset is more shorter and thicker. It is usually found in aquatic plants like water hyacinth and Pistia. It bears a cluster of leaves near the water or ground level and gives adventitious roots inside water or ground from all nodes, e. Like the stolon the sucker is also a lateral branch but it grows obliquely upwards and gives rise to a new plants e. These modified aerial stems perform unusual functions.

Different forms of these stems are the following Fig. It is a leafless, spirally coiled branch formed in some climbers and helps them in climbing neighbouring objects; they may be modification of axillary bud, e. Stem thorn is a hard, straight and pointed structure; it is a defensive organ; also helps in climbing; originates from axillary or terminal bud, e. It is a green, flattended or cylindrical stem which takes the form and function of leaf.

It contains chlorophyll and is responsible for carrying on photosynthesis. It bears succession of nodes and intemodes at long or short intervals. Phylloclades are found in xerophytic plants where the leaves either grow feebly or fall off early or modified into spines e.

Phylloclade with one or two internodes is called cladode e. In Asparagus cladodes are needle-like, slightly flattened green structures which appear in cluster in the axil of a scaly leaf. Main stem bears leaf spines at its nodes. A scale leaf is found just above the spine. Every branch on main stem bears only scale leaves. In the axil of scale leaves cluster of cladodes appear.

Bulbil is the modification of vegetative or floral bud. It is swollen due to storage of food. It can function as an organ of vegetative propagation e. A thin transverse section of a young stem reveals the internal structure when observed under me microscope:. It forms the single-celled outermost layer of the stem.

The outer wall of epidermal cells is cutinized. It bears multi-cellular hairs and a few stomata. It is protective in nature. It is formed of 4 to 5 cell thick layer of collenchymatous cells. These cells are living and contain chloroplasts. It lies below the hypodermis. It consists of a few layers of thin- walled parenchymatous cells with intercellular spaces.

Some of the cells have chloroplasts and they are known as chlorenchyma. It is the innermost layer of cortex. It is made up of single row of compact barrel-shaped cells without intercellular spaces. Jasmine and colocasia are plants with stolons. In some plants, the stems growing above ground are modified to perform certain functions like photosynthesis, food storage, vegetative propagation, protection, climbing, etc.

A bulbil is an aerial stem modification that develops from the axillary bud of a plant or in place of an inflorescence or flower. It then gives rise to a new plant. Bulbils thus allow the parent plant to reproduce vegetatively. The young plants are clones of the parent plant.

In plants like Dioscorea, condensed axillary buds form bulbils while in lily, the floral buds develop into bulbils. Thorns are sharp, hard or woody pointed structures that grow from arrested axillary or terminal buds of the main stem. Thorns occasionally bear flowers or leaves. Duranta and Citrus thorns are modified axillary buds while Carissa thorns are modified terminal buds. Thorns serve various purposes like checking evapotranspiration, defense, and climbing. Thorns can be branched as in Carissa carandas.

Cladodes are stems that get flattened to perform photosynthetic functions of the leaf. Leaves in such plants are often reduced to scales.

While a section of botanists regards cladodes and phylloclades as the same, others differentiate between the two terms. According to the latter, phylloclades are green, fleshy, and flattened stems or cylindrical branches that can grow in an unlimited manner. Here, the leaves are modified to scales or spines and the photosynthetic functions of the leavers are performed by the modified stems. Examples include Opuntia, Casuarina, etc. They also help repair and heal wounds.

In addition, some parenchyma cells store starch. 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.

Vascular tissue composed of xylem red and phloem tissue green, between the xylem and cortex surrounds the pith. Collenchyma cells are elongated cells with unevenly-thickened walls. They provide structural support, mainly to the stem and leaves. These cells are alive at maturity and are usually found below the epidermis. Collenchyma cells in plants : Collenchyma cell walls are uneven in thickness, as seen in this light micrograph.

They provide support to plant structures. Sclerenchyma cells also provide support to the plant, but unlike collenchyma cells, many of them are dead at maturity. There are two types of sclerenchyma cells: fibers and sclereids. Both types have secondary cell walls that are thickened with deposits of lignin, an organic compound that is a key component of wood. Fibers are long, slender cells; sclereids are smaller-sized. Sclereids give pears their gritty texture.

Humans use sclerenchyma fibers to make linen and rope. Sclerenchyma cells in plants : The central pith and outer cortex of the a flax stem are made up of parenchyma cells.

Inside the cortex is a layer of sclerenchyma cells, which make up the fibers in flax rope and clothing. Humans have grown and harvested flax for thousands of years. In b this drawing, fourteenth-century women prepare linen. 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.

As with the rest of the plant, the stem has three tissue systems: dermal, vascular, and ground tissue. The dermal tissue of the stem consists primarily of epidermis: a single layer of cells covering and protecting the underlying tissue. Woody plants have a tough, waterproof outer layer of cork cells commonly known as bark, which further protects the plant from damage. Epidermal cells are the most-numerous and least-differentiated of the cells in the epidermis.

The epidermis of a leaf also contains openings, known as stomata, through which the exchange of gases takes place. 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. Trichomes are hair-like structures on the epidermal surface. They help to reduce transpiration the loss of water by aboveground plant parts , increase solar reflectance, and store compounds that defend the leaves against predation by herbivores.

Stomata : Openings called stomata singular: stoma allow a plant to take up carbon dioxide and release oxygen and water vapor. The a colorized scanning-electron micrograph shows a closed stoma of a dicot. Each stoma is flanked by two guard cells that regulate its b opening and closing.

The c guard cells sit within the layer of epidermal cells. The xylem and phloem that make up the vascular tissue of the stem are arranged in distinct strands called vascular bundles, which run up and down the length of the stem. Both are considered complex plant tissue because they are composed of more than one simple cell type that work in concert with each other. When the stem is viewed in cross section, the vascular bundles of dicot stems are arranged in a ring. In plants with stems that live for more than one year, the individual bundles grow together and produce the characteristic growth rings.

In monocot stems, the vascular bundles are randomly scattered throughout the ground tissue. Vascular bundles : In a dicot stems, vascular bundles are arranged around the periphery of the ground tissue. The xylem tissue is located toward the interior of the vascular bundle; phloem is located toward the exterior. Sclerenchyma fibers cap the vascular bundles.

In b monocot stems, vascular bundles composed of xylem and phloem tissues are scattered throughout the ground tissue. Xylem tissue has three types of cells: xylem parenchyma, tracheids, and vessel elements. The latter two types conduct water and are dead at maturity. Tracheids are xylem cells with thick secondary cell walls that are lignified. The braches start forming some distance above the ground.

In a shrub, there are many thin stems, which have many branches. Trees grow taller than shrubs. The stems in plants have many functions. The stem transports water and dissolved mineral salts from the soil to the leaves.

Inside the stem, there are many small tubes through which the water and mineral salts travel to the leaves. After the food has been made in the leaves, it moves downwards through different tubes in the stem to the roots for storage.

In some plants, green stems can also make food for the plant. They may even be used to store food. The other main function of the stem is to support the leaves so that they can receive plenty of sunlight and air.