Stem – Characteristics and Functions
The scientific field of morphology is concerned with the examination of the composition, traits, and forms of living things. Despite the great structural variation that amazes us in flowering plants (Angiosperms), they all have a few things in common. Examples include roots, stalks, leaves, flowers, fruits, and seeds. As a result, all angiosperm plant morphologies may share these five characteristics. However, if you look closely at a plant, you’ll note that they always have root and shoot systems, and within them, the plant may or may not have flowers and fruit. Plant morphology helps us understand its complex components. Angiosperms, or flowering plants, are plants that produce flowers. The plant has 5 main parts, i.e., roots, stems, leaves, flowers, fruits, and seeds. These parts perform different functions in their own way. Let’s have a glance over the part “the stem”.
The plant’s stem is a crucial component as well. The portion of the plant axis that is ascending is what produces the branches, leaves, flowers, and fruits, as well as aids in mineral and water conduction. It is the plant’s aerial part, formed from the plumule of an embryo or germination of seeds. Initially, green, young stems gradually grow brown and woody. The stem can take on a variety of shapes depending on its purpose.
Plants’ stems give them axial stability. They are autotrophic and grow above ground. They develop away from the ground and toward the light. There is a terminal bud at the stem’s tip. Young stems are colored green. The stem of the plant develops a strong, brown protective covering as it matures into a tree.
Characteristics of Stem
- The stem develops from the embryo’s plumule and epicotyl.
- The erect stem extends away from the ground in the direction of the light.
- There is a terminal bud at the stem’s tip.
- Angiosperm shoots are separated into internodes and nodes.
- Young stems are green and photosynthetic.
- Multicellular hair can be seen.
- The stems and branches of mature plants yield fruits and flowers.
Functions of Stem
- It holds fruits, flowers, and leaves in place.
- The stem enables the leaves to position themselves so they can receive direct sunlight and effectively carry out photosynthesis. Gas exchange is also made possible by the arrangement and positioning of leaves.
- The vascular bundles of stems include the xylem and phloem, which transport water and minerals throughout the plant.
- Flowers and fruits are carried on stems in a way that promotes pollination, fertilization, and seed dispersal.
- To hold food and water, some stems are modified. Think about succulents.
Morphology of Stem of Angiosperms
Nodes and internodes, the two key elements, are shown by the morphology of stems. Internodes are the spaces between nodes, which are where a plant bears leaves. Phyllotaxis is the study of how leaves are arranged on stems. Thus, one leaf per node is referred to as a spiral arrangement in phyllotaxy, while one leaf per node with a 180-degree divergence is the alternate layout. The opposite pattern is referred to as having two leaves per node, and a whorled arrangement is referred to as having more than two leaves per node.
Structure of Stem
Nodes and internodes are formed in the stem. The nodes support the buds that develop into branches and leaves. Two nodes are divided by internodes. Internally, it consists of three fundamental tissue types: vascular, dermal, and ground tissues, all of which are composed of simple cells.
- Dermal tissue: The dermal tissue, which is the stem’s outer tissue, is made up of a single layer of cells termed the epidermis. This tissue guards the underlying tissue and covers the stem. Woody plants have bark, an additional layer of defense over the epidermis. In some instances, the multicellular hairs and a few stomata of the bears.
- Vascular Tissue: Vascular bundles, which run up and down the length of the stem, are composed of the separate strands of the xylem and phloem that make up the stem’s vascular tissue. Both are regarded as complex plant tissues due to the presence of various simple cell types that collaborate with one another. Dicot stems have vascular bundles that are organized into a ring when the stem is cut crosswise. Individual bundles combine to form the recognizable growth rings in plants with stems that survive for longer than a year. The vascular bundles in monocot stems are dispersed throughout the ground tissue at random.
- Ground tissue: It separates into two parts: the cortex, which is located between the vascular tissue and the epidermis, and the pith, which is the center section.
Cortex of stem
The cortex’s primary job is to support and carry out metabolic functions. The sort of cells present determines the cortex’s specialized function. Cortex can be divided into a few parts:
- Hypodermis: It is the cortex’s outermost layer. Collenchymatous cells in a layer of 4 to 5 cells thick make up this structure. These cells have chloroplasts and are live organisms.
- General cortex: It is found beneath the hypodermis. It is made up of parenchymatous cells with thin walls and intercellular gaps. Chlorenchyma is the name given to certain cells that have chloroplasts.
- Endodermis: It is the innermost layer of the cortex. It is composed of a single row of tightly packed, intercellularly closed barrel-shaped cells. Endodermis cells are referred to as the starch sheath because they contain starch grains. Endodermal cells clearly display Casparian strips.
Modifications of Stem
Stems serve a variety of purposes in many plants, including perennation, vegetative reproduction, food storage, synthesis, etc. In addition to axial stability, plants’ stems change under specific circumstances. In order to maintain the plant’s health and growth despite the shifting environmental factors, the modified stems perform functions such as protection, vegetative propagation, food synthesis, and others.
Based on the type of modifications, stem modifications can be classified into Aerial modifications, Subaerial modifications, and Underground modifications.
Aerial Stem Modifications
The aerial stem is a stem that grows vertically or erect above the earth. The two types of aerial stems are reduced stems and erect stems. Aerial stem modifications serve a variety of unique purposes, including climbing, food storage, plant protection, and vegetative propagation. The aerial stem can be modified in 6 different ways.
Tendrils, which are green structures that resemble leafless threads and are utilized for climbing, are modified versions of the plant’s stem or branches. A scale leaf can be observed at the branching point of these tendrils, which can also be unbranched. Tendrils can be categorized into the following four categories.
- Axillary tendrils: Example: Passiflora
- Extra axillary tendrils: Example: Cucurbita
- Floral bud tendrils: Example: Antigonon
- Apical bud tendrils:Example: Grapevine
These are sharp, solid, or woody objects that occasionally have leaves and flowers. Additionally, they may branch. Thorns, which are altered axillary buds, are seen on plants including Duranta and Citrus. Thorns are utilized for climbing or defense. They control breathing as well.
These flattened or cylindrical branches are fleshy in nature. The leaves change into spines or scales, and they control transpiration as well. Phylloclades store water and participate in photosynthesis. Euphorbia, coccoloba, etc.
These flattened or cylindrical branches, also known as cladodes, aid in photosynthesis. Contrary to asparagus (another cladode), which has one long internode, Ruscus has two long internodes.
These are modified vegetative or floral buds that have food reserves for the plant’s body. They are designed to be multiplied vegetatively. Bulbils split off to form new plants. Example: In lilies, the floral buds develop into bulbils, unlike in Dioscorea, where bulbils are compressed axillary buds.
The corolla, calyx, and androecium, together with other floral organs, are carried by the thalamus, which is a compressed stem axis.
Subaerial Stem Modification
In a stem of this kind, a portion of the stem remains underground while the other portion develops aerial roots. On the stem, a dormant bud becomes active and forms lateral branches for vegetative reproduction.
These modified stems have both aerial and subsurface portions. Their general traits are as follows:
- These plants have thin aerial branches.
- Adventurous roots become nodes.
- The stem’s node has the capacity to develop into a complete plant.
- They have sub-aerial stem modifications for vegetative reproduction.
- These plants are called creepers.
A form of creeping stem with lengthy internodes is called a runner. They carry scale leaves, adventitious roots, and scale leaves as they move horizontally across the soil surface. The axillary bud is where this kind of steam emanates. Numerous runners can be produced by a mother plant in all directions. They eventually separate and develop into new plants. Examples include lawn grass and wood sorrel.
Sucker stems emerge from the main stem’s underground basal region. They initially expand horizontally below the soil before obliquely expanding upward. Before detaching from the mother plant, the stem grows an adventitious root system and a leafy shoot. Chrysanthemum and mentha, for instance (Pudina).
A weak lateral stem emerges from the base of the main stem. It eventually bends down to touch the ground after growing aerially for some time. A new shoot and adventitious roots are produced by this plant’s terminal bud. Jasmine and colocasia, for instance.
The one internode on this short runner is by itself. It begins as a leaf axil, grows into a short horizontal branch, forms a rosette of leaves above, and then begins to form adventitious roots below. In aquatic plants, this kind of stem alteration is typically seen. Pistia, eichhornia, and other examples.
Underground Stem Modification
Underground stems are, as their name suggests, stems that emerge from the ground. Most of these stems aid in reproduction, permanency, and the storage of food, water, or minerals. These include, but are not limited to, corms, rhizomes, bulbs, and tubers.
It is used by plants that alter their stems underground to persist and store nourishment. Each year, these plants generate aerial branches. Although they resemble roots, they can be distinguished by the following features. The key characteristics are:
- Internodes and nodes are seen.
- Scale leaves, buds, and adventitious roots can be found at the nodes.
- Instead of resembling a root, the internal structure is more like an aerial stem.
It is a fleshy, non-green subterranean stem with internodes and nodes. Dry scale leaves with axillary buds can be found at the nodes. Moreover, terminal buds are seen. The accidental roots start on the bottom sides. A root-stock rhizome is a name given to the rhizome stem that grows obliquely; straggling rhizomes are the names given to the stems that grow horizontally. Bananas and aloe are two examples of rootstock rhizomes. Ginger and turmeric are two examples of straggling rhizomes.
This kind of modified stem resembles a discoid stem that has been densely compressed. There are several fleshy-scaled leaves and a terminal bud on the upper surface. There are several adventitious roots at the bulb’s base. These bulbs may have tunics or scaly skin. A sheath of dry, membrane-scale leaves, known as a tunic, will envelop a tunicated bulb. There won’t be a tunic when it comes to scaly bulbs. Onions and garlic are examples of tunicate bulbs. Lily is an example of a scaly bulb.
This is a compact rhizome that develops vertically. It is roughly spherical in shape and has a base that flattens out. Its internodes and nodes are clearly round. Scale leaves and axillary buds can be visible on the nodes, and adventitious roots can be observed at the base or all over the body. Crocus, for instance, and colocasia.
It is a corry-covered, swelling tip of a subterranean lateral stem. The eyes are a number of depressions in the skin. Every eye, which is a node, has one or more buds that are protected by a leaf scar. Its connection to a stolon is shown by a large scar at one end, also referred to as the potato heel end. In general, tubers lack adventitious roots. as in potatoes.
FAQs on The Stem
Question 1: What are the main functions of the stem?
- It produces and sustains fruit, flowers, and leaves.
- The placement of the numerous appendages borne on the stem ensures that they may properly perform their respective roles.
Question 2: What are creepers?
A creeper is a plant that spreads its stems or branches outward while growing along the ground.
Question 3: How do plant stems grow?
In most cases, a plant’s stem develops upward (except in some plants). It gets wider and longer thanks to the layers’ ongoing cell growth.
Question 4: Define stem.
The plant’s stem is a crucial component as well. The portion of the plant axis that is ascending is what produces the branches, leaves, flowers, and fruits, as well as aids in mineral and water conduction.
Question 5: What are nodes and internodes?
The two main components of the stem are nodes and internodes. Buds, leaves, branches, etc. are kept in the nodes. A space between two nodes is known as an internode.
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