Anatomy of Stems

The stem is the longest part of the plant, connecting the roots with the leaves. The stem transfers all the nutrients and water from the soil to the leaves, where they are converted into useful products by the process of photosynthesis. The stem then transfers these useful products to all parts of the plant. 

Stems are the parts that connect roots to the top of the plant or tree, where new leaves and flowers are formed. Stems can be divided into three categories:

• Herbs and vegetables have herbaceous stems that are green and soft.
• Trees and shrubs have woody stems like arboreal stems.
• The stem of a succulent is soft and spongy, for example, the stem of a cactus.

Water, nutrients, sap, and minerals are carried throughout the plant by vascular tissues located in the stem. The stem is a long, narrow cylindrical part of a plant. The stem contains phloem and xylem tissues and branches out near the top. Sugars produced in the leaves are delivered to growing parts of the plant via the phloem through translocation, or movement of sugar. The xylem distributes water and dissolved nutrients and minerals upward through the plant, from the roots to the leaves.

General features of the stem

On its external region, stems have nodes that connect the stem to the root or another stem. They also contain leaf scars, which are the marks left by a leaf after it falls off the stem. Internally, the stem contains vascular bundles and nutrient transport knots. Plants also have a pith, a tissue in the stems of vascular plants that run vertically from the roots to the area where the leaves attach themselves. The anatomy of a stem begins at the node that connects it to a root or another stem.

• The epidermis consists of five layers, the outermost of which is called the stratum corneum, which constantly sheds dead skin cells. Then is the stratum lucidum, which is composed of living cells. After that comes the stratum corneum, a smooth layer of cornified material that protects the underlying layers.
• The stem consists of three types of tissues: epidermis, vascular, and ground tissues, all made up of simple cells known as keratinocytes and fibroblasts.

Stem Anatomy

• The stem epidermis-the top layer of cells that make up the stem-is composed of a firmly packed basal lamina and is covered by a thin fingernail skin. The xylem is seen as the focal point of this structure, surrounded by the phloem.
• The stem cells divide, with one daughter cell becoming the primary xylem and the other auxiliary xylem. Stems usually require true meristems but have a few scattered ones.
• The cells in a stem can be separated into equal or transverse pushes along the length of each sieve tube. The phloem transports food.
• Sieve tubes are in charge of transporting food materials and cell by-products throughout a plant and mechanically purging cells.

Anatomy of the dicot stem

A vascular group surrounds the substance in a dicot stem. It is an open, bilateral, and joint vascular bundle. Dicotyledonous stems or dicot stems contain two cotyledon leaves or early leaves.

1. Epidermis

• Parenchymatous cells form a protective outermost layer without intercellular spaces.
• An epidermal layer with multicellular hair (trichomes) encloses the external dividers of epidermal cells.

Cortex

• There are not many layers of collenchyma cells beneath the epidermis of the stem, which form the hypodermis. This provides mechanical stability to the stem.
• The layer beneath the hypodermis has prominent intercellular spaces with several layers of chlorenchyma cells. Pitch-like channels also exist here.
• Parenchyma cells make up the third layer. These cells store food resources.

Endodermis (starch sheath)

• There are no intercellular spaces between the barrel-shaped cells in this layer, and the cells are arranged minimally.
• This layer is also referred to as a starch sheath due to the abundance of starch grains within these cells.

Stele

• There are pericycles, vessels, and piths in the stele.

1. Pericycle (Bundle)

• The pericycle is present between the layers of sclerenchyma cells that are located between the endodermis and vascular groups.

Vascular bundles

• A vascular group in the stem of a dicot is organised around its essence in a ring.
• It has two complete rings, open and endarch rings.

Pith

• There are intercellular spaces between the parenchyma cells that make up the focal piece called the pith.
• Pith rays or medullary rays are the expansions between vascular packs.
• The piths store food for use later on.

Anatomy of monocot stem

On the monocot stem, there are fibrous bundles of vessels close to the base that separate the vascular bundles from parenchymatous ground tissue. Dicot stems surround parenchyma cells in areas with bundles attached in a ring.

Epidermis

• This is the peripheral layer, composed of single cells with thick epidermis-like skin filled with firmly stuffed parenchymatous cells.
• The epidermis does not proliferate.

Hypodermis

• Plants receive mechanical stability from the hypodermis, which consists of several layers of sclerenchymatous cells beneath the epidermis.

Ground tissue

• It does not show differentiation unlike the endodermis, cortex, pericycle, and pith.
• There are a few layers of parenchyma cells enclosing visible intercellular spaces at the surface of the ground tissue.
•  Food is stored in the ground tissue.

Vascular bundles

• The parenchyma ground tissue is dotted with vascular bundles.
• There are a variety of vascular bundles in the fringe segment, which are small and well organised.
• Around the middle are large, roughly organised bundles.
• There is a sheath of sclerenchyma filaments surrounding each vascular bundle.
• Valves are categorised into conjoints, collaterals, endarchs, and closed.

Phloem: In monocot stems, phloem can be found in the form of sieve tubes and companion cells. Phloem parenchyma and filaments are absent.

Xylem: Two metaxylem vessels are found at the top of the stalks; a couple of protoxylem vessels are at the bottom. A protoxylem lacuna forms when the least protoxylem crumbles in a fully developed bundle.

Conclusion

The stem consists of three basic types of cells: parenchyma, collenchyma, and sclerenchyma. These cells are thought to be accountable for metabolic activities like fixing and healing wounds and storing starch. As a result, the stem comprises three tissues, including the epidermis, vascular tissues, and ground tissues, all of which are composed of well-organised cells.