Trunk Anatomy: Monocots and Dicots | botany (2023)

In this article, we will discuss the stem of monocotyledonous and dicotyledonous plants using their respective diagrams.

The stem is part of the axis that supports the leaves and reproductive bodies and is aerial in nature. The close association of stem and leaf, evident from the use of the word "shoot" to refer to both structures, makes their structure quite complex. In addition, the shape of the stem is very variable.

It can be an elongated structure with prominent nodes and internodes, or a compact structure with visible nodes and internodes and leaves clustered in a rosette or bulb, it can also be climbing or creeping. Sometimes the trunk is underground (rhizome, tuber, bulb and tuber). All these varieties and the variable arrangement of leaves on the stem complicate its structure.

The type includes three tissue systems: epidermal, terrestrial and vascular. Differences in the original stem structure are mainly due to differences in the relative sizes of the vascular system and the underlying tissue.

In dicotyledonous plants, the vascular system forms a hollow cylinder surrounded on both sides by the basal tissues, bark and medulla. The vascular bundles are separated from each other by wide gaps in the parenchyma, medullary rays (also in the underlying tissue) or interfascicular parenchyma of medullary rays. It connects the core and the bark.

In the monocotyledonous stem, the arrangement of vascular tissue is quite complex. In these cases, as with some dicots, the tufts occur in more than one ring or are dispersed across the stroma section. The outlines of the underlying tissue in the cortex and medulla may not be visible.

The main anatomical features of the stem are as follows:

(1) Protoxyl is always endarch, i.e. H. facing the center, i.e

(2) The vascular bundles are interconnected and lateral.

The stems of the two main groups of angiosperms are of different structure; Therefore, here are some examples for each group separately.

Monokotyler Stamm:

A. Corn stalk:

It represents a typical monocotyledonous stem and has the following structure:

1. Epidermis:

It is the outermost layer of the stem. The cells are compact and heavily cut on the outside. The hairs on the stem are absent. Stomas may be present.

2. Subcutaneous:

The area below the epidermis is called the subcutaneous tissue. It consists of 2-3 layers of sclerenchyma. In the area of ​​the stomata, it may be interrupted by the flesh.

3. Core Tissue:

It extends from the subcutaneous tissue to the center of the stem and includes thin-walled parenchyma cells with intercellular spaces.

4. Vascular bundle:

These are cumulative, hedging and closed contracts. Numerous vascular bundles are irregularly distributed in the underlying tissue. The bunches are smaller and more numerous around the circumference, and smaller and larger towards the center. Each bundle is surrounded by a sheath of sclerenchyma. In the external bundles, the sheath may continue with the subcutaneous tissue.

The xylem in each bundle is arranged in a Y shape. Both arms of the Y occupy two large vessels (metaxylem, cicatricial), and the tail - smaller vessels (protoxylem-annular and helical). There is a lysogenic water cavity on the inside of the protoxylem. It is formed as a result of rupture of protoxylem vessels.

The phloem is above the xylem. It includes only sieve tissue and support cells. There is no bast pulp. The primary phloem (protophloem) is usually pushed out and crushed.

B. Asparagus stalks:

An example of this is asparagus. In this strain, the epidermis is a layered flesh with more or less rounded cells. The skins are also well developed. There are clear cracks in the epidermis followed by subdental defects. Just below the epidermis is chlorenchyma called the cortex.

The innermost layer of the bark, probably called the starch sheath, is visible. The bark has a compact strip of 5-6 layers of sclerenchyma cells that is attached to the soil (compared to normal strains where the sclerenchyma is just below the epidermis).

Vascular bundles differ from maize bunches in that they have more metaxylem and lack the water cavity and cuticle. The xylem forms a V-shaped structure and the bundles are irregularly distributed in the underlying parenchymal tissue. The stem is empty. The structure of the asphodelus stem is also quite similar to the asparagus stem.

C. Scape (flower stalk) Canna:

Also in this variety, the epidermis consists of one layer of compact flesh with a well-developed cuticle, followed by a two- or three-layer zone of flesh. This zone can be called the hypodermis (compared to maize and other monocots, where it is sclerenchyma) and is lined on the inside with a continuous layer of chlorophyll tissue. Below are small spots of sclerenchyma.

The vascular bundles are diffuse, connected, lateral and closed. The bundle sheath is incomplete on the sides. It is only found on the outside and inside and is more pronounced on the outside. The xylem has one large and several smaller vessels with spiral protrusions. The phloem is external and contains sieve tubes and companion cells. The water cavity is insufficient.

D. Which tribe:

The wheat stalk also has some typical characteristics. Here, too, we have a well-developed, single-layer epidermis, which, however, is interrupted here and there with pores and cracks. The protective cells of the stomata are slightly indented in the subcutaneous part. Usually in this case, alternating spots of chlorenchyma and sclerenchyma are visible in the subcutaneous tissue.

Stomata are present only above the chlorenchyma in the epidermis. Sclerenchyma extends in the lower part and forms a continuous belt there. Beneath this ring of sclerenchyma are numerous vascular bundles that are scattered throughout the underlying parenchyma. The vascular bundles are closed, lateral and surrounded by a sclerenchymal sheath. The xylem is usually Y-shaped. The stem has a hollow in the middle.

E. Doob-Grasstamm (Cynodon Dactylon):

An exceptional case is a boat with monocots.

In this case, there is generally a thick cuticle followed by a single cuticle layer, but the cell walls are woody. Beneath the epidermis is the chlorenchyma followed by the sclerenchyma. This is a distinguishing feature of such a strain and differs from most monocotyledonous strains in which the epidermis is followed by sclerenchyma.

The vascular bundles show the typical characteristics of a monocotyledonous stem as they are lateral, closed and diffuse. Sometimes they form 2 rings. They also have a Y-shaped xylem below the phloem, a water cavity, and a fascicle sheath (sclerenchyma). All these bundles are irregularly distributed in the parenchymal stroma.

Two-part tribes:

A. Cucurbita-Stamm:

Cucurbita is a typical species of the gourd family, most members of which have a similar internal structure. It is a hollow trunk with five protruding ridges, alternating with the same number of furrows.

The internal details show the following:

1. Epidermis:

It is the outermost layer with several multicellular shoots and a cuticle. The cells are compact.

2. Subcutaneous:

It is collenchymatous and more prominent under the ridge, with about 6-7 rows of cells. In furrows, it consists of one or two layers of cells and carries chloroplasts.

3. Kortex:

As a result, narrow, two- or three-layer strips of flesh form under the subcutaneous layer. Cells contain chloroplasts and have intercellular spaces.

4. Endodermis:

It is a single, corrugated layer of barrel-shaped cells containing starch granules. It is outside the pericycle.

5. Perizikel:

Below the endoderm is a continuous zone of 4-5 layered sclerenchyma. This is called a homogeneous pericycle.

6. Vascular bundle:

There are 10 vascular bundles arranged in two rings. There are five rollers in each ring. In very few cases, the number of beams may exceed this value. The outer bundles are smaller and lie below the ridge. The inner beams are larger and are located below the grooves. Each package is bonded, patented and reversible.

Sieve tubes are very visible in the phloem. Methoxylem contains two or three vessels with large pits, and protoxylem has many small vessels with an annular or spiral thickening. There is a belt of cambium on either side of the xylem. Outside the cambium, there is a phloem stain on both sides.

7. Core Tissue:

The thin-walled tissue extending below the pericycle into the medullary cavity is called the underlying tissue. Vascular bundles are embedded in it. There is a large parenchymal distance between the outer beams, but the distance between the inner beams is shorter so that in some cases the bundles are almost connected.

B. Sunflower stems:

The stems of almost all representatives of the daisy family have a typical cross-sectional structure.

1. Epidermis:

This is the outermost layer. It contains tangentially flattened cells that are closely connected by radial faces. There is usually a cuticle on the outer surface. Some cells have multicellular hairs and stomata may be present in some cells. Chloroplast is always absent.

2. Kortex:

The tissue beneath the epidermis is called the cortex and can be divided into three areas:

(a) subcutaneous tissue:

The outermost part of the cortex consists of several layers of collenchyma cells. Due to the thickening of the cells in the horns, there are no intercellular spaces.

(B)General cortex:

The tissue below the subcutaneous tissue consists of several layers of parenchyma and is called the general cortex or cortex. In this tissue, the intercellular spaces are well defined.


It is the innermost layer of the cerebral cortex. It contains barrel-shaped, close-fitting cells without intercellular spaces. It contains starch granules and therefore can also be called starch coating.

3. Perizikel:

The tissue between the vascular bundles and the endoderm is called the pericycle. It includes the sclerenchyma (above V.Bs.) which alternates with the flesh and may be called a heterogeneous pericycle. The sclerenchyma associated with the phloem is called hard lichen.

4. Vascular bundle:

The vascular bundles are connected, lateral and open. They are arranged in a ring and usually include xylem, phloem and cambium.

5. Tick:

This is the middle part of the stem. It consists of numerous rounded or polygonal thin-walled living cells with noticeable intercellular space.

C. Peristrofenstam:

The peristtrophic tree has a single layer of epidermis. The skins are also well developed. Subcutaneous fat, which consists of collenchyma, is found only in the groin area, while collenchyma is absent elsewhere. The bark consists of large parenchyma cells arranged in 2-3 layers and is chlorenchymatous.

The endoderm forms a watertight space between the vascular tissue and the cortex. It is a typical single layer of barrel-shaped cells. The pericycle consists of several layers of flesh and is mixed with the phloem. The vascular bundles are lateral and arranged in an annulus. The core is well developed, spinal rays are also present (Fig. 8.13).

D. Shared Role:

In this case, it is a single-layer epidermis with a uniform, medium-thick scale. Under the epidermis, the subcutaneous tissue is well developed and has 5-8 layers of collenchyma. The bark is very small, having only two to several layers. There are oil cavities in the bark. The endoderm is well represented by a typical barrel-shaped layer of cylindrical cells.

The pericycle is heterogeneous with smaller patches of sclerenchyma. The vascular bundles form a ring, are lateral, open and connected. In the center is a core of well-developed parenchyma. The parenchymal medullary rays are also clearly visible.

Based on the general structure, the tribes are divided into four main types:

i Drvenasti dikotiledon:

In these strains, the interfascicular areas are narrow and usually only visible at a young age. Primary xylem is insignificant after secondary growth, and secondary xylem is the main part. The rays are generally narrow, but in the phloem region, i.e. H. in Tilia and Michelia etc., they are arcuate.

II. Herbaceous dicots:

In most cases, they resemble young logs. The inter-bundle area of ​​these trees is marked by a wall. The primary xylem generally remains clearly visible even after secondary growth.

iii. Dikotiledon vinove loze:

In these trunks, the primary vascular bundles are separated by wide interfascicular areas. Vascular bundles are generally large and small. In some cases, the pericycle is sclerenchymatous, e.g. B. in Cucurbita and Aristolochia, while in other cases, e.g. Thunbergia, it shows scattered sections of sclerenchyma. Secondary growth is in many cases limited to the bundle area.

IV. Herbaceous monocots:

These shoots generally have no secondary growth and only increase in thickness as a result of primary growth. They have a uniform basal tissue with diffuse vascular bundles. The bundles have a Y-shaped xylem and bundle cover.

knot anatomy:

The vascular system of the leaf continues into the vascular system of the stem. This relationship is observed in the region of stem nodes. In this part, the band of stem bundles moves towards the leaf. Such a bundle, which extends from the base of the leaf to join the band in the stem, is called a leaf path.

The leaf footprint can thus be described as the caudal portion of the leaf's vascular supply. At the node where the leaf path begins, there is an area of ​​flesh in the vascular cylinder of the stem called the leaf cleft. Thus, leaf spacing is due to the origin of the leaf trace.

The number of marks and gaps on the leaves varies even within the same plant. These differences have phylogenetic significance. Special expressions are used to describe the anatomy of a knot. The term "gap" is used instead of "gap", and nodes are called monolacunar, trilacunar, and multilacunar depending on whether a leaf is associated with one, three, or more gaps in a node. If more than one leaf is attached to a node, the lacunar state is described in terms of a single leaf. To be clear, if each leaf is connected by a gap, a node is called a non-lacanathy, regardless of whether there are actually two or more gaps.

For some plants, namely clerodendrons, there is a special condition. Two leaf paths are assigned to one gap. This is a primitive state, called a two-lane unilateral state.

The evolutionary sequence can be described as follows:

(i) Duplicate Unilacunar, Trilacunar and Multilacunar

(ii) Double Monolacunary, Single Monolacunary, Trilacunary and Multilacunary.

The one-liner may have originated from a trilacunar situation.

The spacing between the sheets also varies in size, both in the lateral and vertical directions. In shoots with many axially elongated inter-tuft areas or in scattered bundles, it is difficult to determine the leaf spacing, so the concept of leaf spacing in these cases is only theoretically applicable. It can be easily recognized by the stems with secondary growth.

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