The stem is one of two fundamental structural axes of vascular plants, the other being the root. It keeps leaves, flowers, and fruits alive, transports water and dissolved substances between roots and shoots in the xylem and phloem, stores nutrients, and regenerates new living tissue in the xylem and phloem. A vascular plant’s stem is one of the two primary structural axes. It refers to the portion of the plant that is above ground. A few stems have been discovered underground and are thought to represent stem alterations.
Structure of a stem:
Nodes and internodes divide the stem. The nodes produce leaves and contain the buds that develop into branches. Two nodes are separated by internodes.
It has three fundamental types of tissues on the inside: dermal tissue, ground tissue, and vascular tissue, all of which are made up of simple cells.
Epidermis:
The epidermis is a single layer of cells that makes up the dermal tissue, which is the exterior tissue of the stem. This tissue protects the underlying tissue by wrapping around the stem and covering it. On top of the epidermis, woody plants have a layer of protection called bark. The multicellular hairs and a few stomata of the bears in some circumstances.
Ground tissue:
The pith, which is between the vascular tissue and the epidermis, and the cortex, which lies between the vascular tissue and the epidermis, are the two parts of ground tissue that split.
There are three layers to the cortex:
- Hypodermis: The hypodermis is the cortex’s outermost layer. It is made up of a layer of collenchymatous cells that is 4 to 5 cells thick. These are live cells with chloroplasts.
- General cortex: The general cortex is located beneath the hypodermis. It is made up of parenchymatous cells with thin walls and intercellular gaps. Chlorenchyma refers to some of the cells that have chloroplasts.
- Endodermis: The cortex’s deepest layer. It consists of a single row of tightly packed barrel-shaped cells with no intercellular gaps. Endodermis cells are known as the starch sheath because they retain starch grains. In endodermal cells, Casparian strips are apparent.
- Complex tissue: The complex tissues xylem and phloem, which carry water and nutrients up and down the length of the stem and are organised in discrete threads called vascular bundles, make up the stem’s vascular tissue. In dicot plants, the cambium is a strip of thin-walled cells that lies between the xylem and phloem. The merismatic cells that make up the Cambium are in charge of secondary growth. Monocots do not have it.
Growth in a stem:
There are two ways for stems to grow:
- Because the merismatic tissue in these areas of the stem divides quickly, primary growth occurs at the apical tips of the stem.
- Secondary growth refers to the thickening of the stem as a result of the lateral meristems. Herbaceous plants lack cambium, which is responsible for this type of growth, hence they lack these features.
Types of stem:
There are three sorts of stems based on their position on the ground:
- Underground stem
- Aerial stem
- Subaerial stem
Functions of stem:
- It retains leaves, flowers, and fruits in place.
- The stem permits the leaves to be arranged in such a way that they get direct sunlight, allowing them to perform photosynthesis efficiently. Due to the arrangement and location of the leaves, gas exchange is also feasible.
- The vascular bundles of stems include xylem and phloem, which transport water and minerals throughout the plant.
- Stems produce flowers and fruits in such a way that pollination, fertilisation, and seed dispersal are made easier.
- Some stems are altered to store food and water. Succulents, for example.
Conclusion:
Stems are primarily responsible for supporting and elevating leaves, fruits, and flowers. The leaves are arranged by the stalk in such a way that they get direct sunlight for photosynthesis. Xylem and Phloem transport water throughout the plant. In stems, food, water, and nutrients are all kept. Meristems are stem cells that give rise to new organs and tissues. The stem comes in three varieties: underground stem, aerial stem, and subaerial stem. A stem serves numerous crucial purposes in addition to allowing you to climb a tree.