Monocot Vs Dicot Stem Overview

Definition of Monocot Stem

Monocot stems are hollow axial parts of the plant that are fashioned like a circle and produce nodes, internodes, leaves, branches, and flowers at their basal end.

• Various monocot species have different stem sizes, although they are rarely as big as dicots.
• Monocot stems are grassy because they don’t have secondary growth since they don’t have cambium in their internal tissue system.
• However, some plants, like bamboo and palms, will possess woody stems due to aberrant secondary growth.
• Many monocot stems are hollow since the tissues in the stem are not grouped in an ordered manner.
• The plumule of the embryo gives birth to monocot stems, which regularly have a terminal bud at the shoot’s end. The stem is favourably phototropic in contrast to the roots.
• At nodes, which are positioned evenly spaced throughout the stem, the stem releases leaves and branches. In monocots, the base of the stem is surrounded by leaves that grow from the nodes without a petiole.
• Depending on the features of the plant species, monocot stems can take on a variety of shapes.
• Monocots have a caudex or columnar form of stem that is unbranched, upright, cylindrical, and strong, with a leafy crown at the top, such as coconut and palm trees. Fallen leaves have left wounds all over the trunk of this sort of stem.
• Monocot plants like bamboo have culm-type stems, which are made of solid nodes and hollow internodes. The tiller branching frequently causes the nodes to swell.
• The absence of an aerial stem during the vegetative stage of the plant distinguishes the kind of stem termed a scape, which is present in certain monocots, including onions. In later stages, a cylindrical, unbranched reproductive stalk with an inflorescence at the terminal is seen.
• Monocot stems are essential because they hold up most of the plant’s parts, from the photosynthetic leaves to the branches and flowers.

Definition of Dicot Stem

Internodes and nodes are the building blocks of the dicot stem, the solid cylindrical axial part of a plant from which grow leaves, branches, and flowers.

• The most defining feature of dicot stems is the stiff, woody trunk that develops during the plant’s secondary growth.
• The diameter of the stem may vary from a mere millimetres to many centimetres depending on the variety of plant and its age.
• Dicots have stems that are initially green and barely photosynthetic, but as the plants grow older, they develop hard, woody stems.
• Since the lateral branches of the cortical zones are where dicot stems originate, they are exogenous in origin.
• Dicot stems are positively phototrophic and also develop from the embryo’s plumule. The stems, as opposed to the roots, feature stomata that allow for the exchange of gases.
• The internode is the space between two nodes, which are nodes that are slightly inflated structures that are found throughout the stem.
• Branches and leaves grow from the nodes.
• Varied kinds of dicots have different numbers of leaves or branches on their stems, which grow with a petiole.
• Although most dicot stems are upright and rising, some may grow prostrate on the ground, as in strawberries or sweet potatoes.
• Similar to how monocot stems are altered according to the species, dicot stems likewise have various structural and functional variations.
• The deliquescent form, in which the main stem develops for a while before ceasing to grow, is a typical stem type in dicots. The plant’s structure takes the form of a dome or an umbrella as it continues to sprout branches.
• Some dicots may be climbers with supple, flexible stems that enable the plant to navigate across uneven terrain and flourish.

Structure of Monocot and Dicot Stem

The following structures make up the dicot and monocot stem’s internal structure or anatomy:

1. Epidermis

• The epidermis is the stem’s outermost layer and is made up of a single layer of cells with thin walls that are tightly packed together without intercellular gaps.
• Although the epidermis’ cells lack chlorophyll, some of them have undergone modification to become trichomes, which are multicellular hairs. Monocot stems are devoid of trichomes.
• The cuticle, a layer of cutin that lies outside the epidermis, protects the tissues below the epidermis.
• Since the stem has stomata for gas exchange, its epidermis differs from that of the roots.
• Since monocots don’t go through secondary growth, their epidermis stays the same throughout the plant’s development. Dicots may have their epidermis replaced during secondary development.
• The protection of the stem’s underlying tissues from various external influences is the epidermis’ most crucial job.

2. Cortex

• The existence of various sections, as well as the quantity and variety of cells, change dramatically between the cortex of monocot and dicot stems.
• The hypodermis, general cortex, and endodermis are the three different sections that make up the cortex in the dicot stem.
• Directly under the epidermis lies the hypodermis, which serves to support the epidermis further.
• Collenchyma makes up the thick, multicellular hypodermis. These cells may prepare nourishment for the plant since they contain chlorophyll.
• Parenchymatous cells are distributed loosely with sufficient intercellular gaps in the general cortical area. The food that the cells of the hypodermis have made is stored by these cells.
• The stem’s overall cortex is made up of mucilage or resin canals that span the length of the stem.
• The endodermis, a thick, single-layered tissue, makes up the deepest layer of the cortex in dicots. This region’s cells are tightly packed and barrel-shaped, with no gaps between them.
• Because its cells contain a lot of starch, the endodermis is sometimes known as the “starch sheath.”
• Due to lignin deposition, which creates Casparian strips, the radial and transverse walls of the endodermis cells are thick.
• The cortical area of monocot stems is made up entirely of the hypodermis. Sclerenchymatous cells make up the hypodermis, which has a thickness of two to three layers.
• The monocot stem’s hypodermis is more rigid, whereas the dicot stem’s is more elastic.

3. Ground Tissue

• The ground tissue in monocot stems is not distinguished into components like pericycles and medullary rays.
• There is a cluster of parenchymatous cells in the ground tissue that extends up to the centre of the hypodermis.
• The cells are organised loosely with intercellular gaps and have thin-walled spherical walls. The arterial bundles stuck in this area are supported by the ground tissue, which acts as their matrix.
• The ground tissue of the dicot stem is distinguished into the pericycle, medullary rays, and pith.

4. Pericycle

• The term “pericycle” refers to the tissue that is situated between the endodermis and the vascular bundles. The dicot stem’s underlying tissues are shielded by the multilayered pericycle.
• The term “hardbast” is frequently used to describe the pericycle because its cells are sclerenchymatous. Above the vascular bundles, sclerenchymatous cells from the pericycle can be seen as semilunar patches.

5. Medullary rays

• The medullary rays, which transmit food and water radially between the vascular bundles, which are a portion of the pith that surrounds the bundles.

6. Vascular bundles

• In monocot and dicot stems, the organisation, quantity, and composition of vascular bundles vary significantly.
• The core pith located below the pericycle is surrounded by a ring-shaped arrangement of vascular bundles on the dicot stem.
• The open, wedge-shaped, collateral vascular bundles are wedge-shaped. The dicot stem has an eustele-type stele.
• The vascular bundles are homogeneous in size and few in number. Each bundle is made up of a strip of cambium separating a patch of phloem from the periphery from the centre from the patch of xylem.
• The stele’s pith contains the xylem, which is made up of tracheids, vessels, xylem parenchyma, and xylem fibres.
• Larger metaxylem and smaller protoxylem units make up the tracheids and vessels. The xylem’s components are organised into rows.
• Phloem can be found as an undifferentiated mass underneath the sclerenchymatous patch of the pericycle.
• The dicot stem has bigger phloem bundles that are made up of phloem parenchyma, companion cells, and sieve tubes.
• The monocot stem contains multiple vascular bundles that are dispersed throughout the ground tissue and cortex. The monocot stem’s stele is an atactostele type.
• Oval, conjoint, collateral, closed, and endarch bundles make up the group. Depending on where they are on the stem, the bundles vary in size. The core has larger bundles, whereas the perimeter contains smaller bundles.
• The bundles are made up of phloem that is present at the edges without any cambium and xylem that is present in the core.
• Monocot stems have fewer xylems and are made up of metaxylem, which has two big vessels, and protoxylem, which has one smaller vessel. The placement of the vessels forms the letters Y or V.
• Between the metaxylem vessels, there are not many tracheids. The dissolution of the xylem components and the parenchyma below has left the schizolysigenous water cavity under the protoxylem channel.
• Outside of the xylem, phloem is found, with part of it clustered near the metaxylem vessels.
• In the monocot stem, companion cells and sieve components make up the phloem. The protophloem is crushed beneath the vascular sheath in mature phloem bundles, leaving just the meta-phloem area.

7. Pith

• Dicot plants have a well-developed pith, whereas monocot stems are less developed and undifferentiated.
• The medullary ray-like cells, which are parenchymatous, surround the vascular bundles.
• The cells can be either polygonal or spherical, and they can have intercellular gaps or not. Food is stored by the cells in the pith area, which also aid in the movement of food and water between the bundles.

Functions of Monocot and Dicot Stem

Some of the roles played by monocot and dicot stems include the following:

• The stem serves as the axis of a plant, supporting many organs and limbs such as leaves, branches, flowers, and fruits.
• Water and nourishment are both transported by the stem from the roots to various regions of the plant and from the leaves, respectively.
• Some plants have young stems that can photosynthesize and prepare nourishment for the plant.
• A significant number of food particles, including starch and other nutrients, are stored in the stem cells.
• Some plants have stems that are specifically designed for activities like climbing and food storage.
• To ensure the growth of the plant, the meristem tissue of the stem constantly produces new live tissue each year.
• The stomata in the stem participate in transpiration and aid in the expulsion of extra water.
• The stems of plants with modified stems resembling cactus hold a significant quantity of water and nutrients to stop water loss.

Examples of Monocot Stems

Palm tree stems

• Various species of palm have different sizes, shapes, and looks. However, the stem often has a cylindrical to slightly tapered shape, with the illusion of periodically bulging.
• The stem’s surface can range from being smooth to being knobby and rough with pointsy spines. Leaf scars on certain stems may show the places where the stem and leaves were connected.
• The stem’s internal organisation is consistent with that of the majority of monocots.
• The stems are made up of a single apical meristem, which is in charge of the development of new cells and plant growth.
• Lignin and cellulose are deposited on the cells by the xylem and phloem parenchyma, strengthening the oldest regions of the palm stem.
• The xylem and phloem of the stem continue to function throughout the plant’s lifespan, which can last for hundreds of years depending on the species.
• Outside the stem’s core cylinder are the tissues of the hypodermis and epidermis, which are together referred to as pseudobark.

Examples of Dicot Stems

Cactus stem

• The stem of a cactus is a modified dicot stem made of fleshy tissue that can hold a lot of water.
• The epidermis consists of thin-walled cells organised in close proximity to one another. The hydrophobic cuticle located outside the epidermis aids in preventing water loss.
• There are tiny stomatal holes in the epidermis, and these are regulated by guard cells. The cortex, vascular bundles, and pith are located underneath the epidermis.
• The most noticeable part of the stem, which is made up of parenchymal cells with thin walls and a long lifespan, is the cortex. The cortex contains cells that are specialised as laticifers and mucilage cells.
• Photosynthesis-capable cells with chlorophyll can be found in the cortex’s inner area. The amount of chlorophyll gradually decreases as one moves further into the area.
• The xylem bundles in the vascular bundles, which are involved in the movement of water throughout the plant body, are more numerous.

References and Sources

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