Anatomy of Dicotyledonous and Monocotyledonous Plants: Meaning, Diagrams

Do you know why the Sunflower and the Orchids do not belong to the same group of flowering plants even though both are flowers? Some plants produce true seeds (Angiosperms) and some do not produce true seeds (Gymnosperms). Based on the number of cotyledons these two flowering plants are differentiated.

The anatomy of dicotyledonous and monocotyledonous plants is different in the case of root, stem, and leaves. Read on to learn more about the Anatomy of dicotyledonous and monocotyledonous plants.

What are Dicotyledonous and Monocotyledonous Plants?

Angiosperms are flowering plants that are divided into two types based on the number of cotyledons. They are monocotyledonous and dicotyledonous plants.
Monocotyledonous plants are those plants that contain only one cotyledon.
Example: Sugarcane, Maize, etc.
Dicotyledonous plants are those plants that contain two cotyledons—examples: Sunflower, Mango, etc.

Anatomy of Dicot Root

The transverse section (TS) of a typical dicotyledonous root shows the following structures:

1. Epiblema: It is the single outermost layer. Epiblema is also known as the piliferous layer. The cuticle is not present. Some cells show tubular outgrowths called root hairs.
2. Cortex: This is just below the epiblema. It is uniform and simple. It consists of several layers of thin parenchymatous cells with conspicuous intercellular spaces. The cells contain storage materials like starch.
3. Endodermis: It is the innermost layer of the cortex that surrounds the stele. They have characteristic bands of lignin and suberin along their radial and tangential walls, known as the Casparian strips or Casparian bands. These strips prevent plasmolysis of endodermal cells and do not allow wall-to-wall movement of substances. Later in the development of the root, all cells of the endodermis become thick-walled, except at positions opposite the protoxylem. These thin-walled cells are known as passage cells.
4. Stele: All the tissues that are present inside the endodermis comprise the stele of the root. These include pericycle, vascular bundles, and pith.
i. Pericycle: It is made up of thick-walled parenchymatous cells. The lateral roots or the root branches originate from the pericycle.
ii. Vascular bundles: The vascular bundles are radial; that is, xylem and phloem occur in separate patches, are arranged on alternate radii. The root may be diarch, triarch, tetrarch, pentarch, and polyarch.
iii. Pith: The pith is generally absent in the dicot root, but if it is present, it is small and consists of parenchyma cells.

Anatomy of Monocot Root

The transverse section (TS) of a typical monocotyledonous root shows the following structures:

1. Epiblema: It is the outermost layer consisting of a single row of thin-walled cells without any intercellular spaces. The structure and fate of this layer are more or less similar to that of dicot roots.
2. Cortex: This lies just below the epiblema. It consists of several layers of parenchymatous cells. It consists of prominent intercellular spaces. The cells are more or less round and contain starch grains.
3. Endodermis: It is the innermost layer of the cortex lies just below the cortex. It is single-layered, and the cells are barrel-shaped. They are provided with Casparian strips or Casparian bands.
4. Stele: All the tissues that are present inside the endodermis comprise the stele of the root. These include pericycle, vascular bundles, and pith.
i. Pericycle: It is the outermost layer of the stele and lies just below the endodermis. It is made up of one or more thick-walled parenchymatous cells. The lateral roots are arises from the pericycle.
ii. Vascular bundles: The vascular bundles are usually polyarchy. The vascular bundle is radial; that is, xylem and phloem occur in separate patches and are arranged on alternate radii.
iii. Pith: The pith is well developed and parenchymatous.

Fig: Transverse Section of Monocot and Dicot Root

Differences between TS of Dicot and Monocot Root

Anatomy of Dicot Stem

The transverse section (TS) of a typical dicotyledonous stem shows the following structures:

1. Epidermis: The epidermis is the outermost and the single layer of cells present in the stem. It carries multicellular trichomes and a few stomata. The epidermis is without intercellular spaces but is provided with a cuticle.
2. Hypodermis: This is just below the epidermis and consists of 3 to 4 layers of collenchymatous cells. The collenchyma cells contain chloroplasts
3. General Cortex: This zone lies just beneath the hypodermis. The cells of this zone are parenchymatous and multilayered. The resin ducts or oil ducts are surrounded by a glandular parenchymatous layer that also occurs abundantly throughout this sub-zone.
4. Endodermis: This zone lies beneath the cortex and is made up of a single layer of barrel-shaped cells. It is the innermost layer of the cortex. These cells possess a greater amount of starch grains, so it is also referred to as a starch sheath.
5. Pericycle: It lies next to the endodermis. The pericycle is in the form of semilunar patches of dignified sclerenchyma cells, which are lignified. Hard bast is the patch that is associated with the phloem of the vascular bundle.
6. Medullary rays: It lies in between the vascular bundles and is made up of parenchymatous cells that constitute medullary rays. These are slightly larger as compared to the other cortical cells.
7. Vascular bundles: The vascular bundles are present in a ring form on the inside of the pericycle. Conjoint, collateral, endarch, and open are different types of vascular bundles found in the dicot stem. It is made up of xylem, phloem, and cambium.
8. Pith: The pith holds the large central part of the stem. It contains rounded parenchymatous cells with plenty of intercellular spaces.

Anatomy of Monocot Stem

The transverse section (TS) of a typical monocotyledonous stem shows the following structures:

1. Epidermis: It is the outermost, single-layered, compact, rectangular composed of living cells. The epidermis is covered by a thick cuticle and contains few stomata. It does not contain any hairs.
2. Hypodermis: This is just below the epidermis and consists of sclerenchymatous cells.
3. Ground tissue: Ground tissue is the entire tissue that lies inside the epidermis, except for the vascular bundles. It contains rounded parenchymatous cells. It consists of distinct intercellular spaces. The ground tissue is not further differentiated.
4. Vascular bundles: Scattered vascular bundles are present throughout the ground tissue. Cambium is absent in the vascular bundle so; secondary thickening does not occur. The vascular bundles are oval and generally surrounded by the bundle sheath cells. It contains the xylem and the phloem.

Fig: Transverse Section of Monocot and Dicot Stem

Differences between TS of Dicot and Monocot Stem

Anatomy of Dicot Leaf

The dorsiventral leaves are found in dicots. These are generally horizontal, and sunlight falls on their upper surface. The anatomical features of dorsiventral leaves are:

1. Upper epidermis: This is generally the outermost single layer made up of parenchymatous cells but sometimes multilayered. The epidermal cells sometimes have outgrowth called papillae found in Gladiolus. The chloroplast is absent in this layer. The stomata are usually absent or less present on the upper surface.
2. Lower epidermis: The lower epidermis is almost similar to the upper epidermis but the number of stomata is more. Chloroplast is absent in this layer except for guard cells of stomata. There are substomatal cavities present below the stomata that help in gaseous exchange.
3. Mesophyll: Mesophyll is a ground tissue that is present in between the upper and lower epidermis. It is divided into two regions-
i. Upper palisade parenchyma is elongated, columnar cells without intercellular spaces and contain abundant chloroplasts. Hence they are the major seat of photosynthesis.
ii. Lower spongy parenchyma is found below the palisade parenchyma and is oval or spherical with intercellular spaces. They contain fewer chloroplasts as compared to the palisade parenchyma.
4. Vascular bundles: Vascular bundles are found scattered in the spongy parenchyma, and the vascular bundle in the midrib region is the largest. Vascular bundles are conjoint, collateral, and closed. Each vascular bundle is enclosed by a bundle sheath of parenchymatous cells. The xylem is present towards the upper epidermis and phloem towards the lower epidermis in the vascular bundles.

Anatomy of Monocot Leaf

The isobilateral leaves are found in monocots. These are generally vertical. The anatomical features of isobilateral leaves are:

1. Epidermis: The leaf consists of upper and lower epidermis made up of single-layered compactly arranged parenchymatous cells. The cells of the epidermis do not possess chloroplasts. Stomata are present on both the upper and lower epidermis (amphistomatic). In the upper epidermis, some large motor cells or bulliform cells are present in groups.
2. Mesophyll: In between the upper and lower epidermis, the ground tissue which is present is called mesophyll tissue., which is not differentiated into palisade and spongy parenchyma. All the cells are alike, which are oval or spherical with intercellular spaces. These cells contain abundant chloroplasts.
3. Vascular bundles: A large number of vascular bundles are present, some of which are small and some are big. Around each vascular bundle, a bundle sheath of parenchymatous cells is present. Vascular bundles are conjoint, collateral, and closed. In the vascular bundle., the xylem is present towards the upper epidermis and phloem towards the lower epidermis.

Fig: Anatomy of Monocot and Dicot Leaf

Differences between TS of Dicot and Monocot Leaf

Differences between TS of Dicot and Monocot Flower and Seed

Summary

There is anatomical variation present between the monocotyledonous and dicotyledonous plants. The vascular bundles are diarch to hexarch in dicot root while hexarch to polyarchy in monocot root. Pith is usually absent in the dicot stem, while the pith is large made up of parenchymatous cells situated in the centre of the stem in the monocot stem. The stomata are usually more on the lower epidermis of dorsiventral leaves, while the stomata are equal in isobilateral leaves. Two cotyledons are present in dicots, while a single cotyledon is present in monocots.

Frequently Asked Questions (FAQs) on Anatomy of Dicotyledonous and Monocotyledonous Plants

Q.1. What is the difference between monocotyledonous and dicotyledonous plants?
Ans: The difference between monocotyledonous and dicotyledonous plants are:
The monocotyledonous plants contain only one cotyledon, while dicotyledonous plants contain two cotyledons.

Q.2. Which type of roots do Monocotyledonous plants have?
Ans: Monocotyledonous plants mainly contain a fibrous root system.

Q.3. Are bananas monocots or dicots?
Ans: Bananas are monocots.

Q.4. How many xylem bundles are present in a monocotyledonous root?
Ans: There are more than six xylem bundles present in a monocotyledonous root.

Q.5. What is a dicotyledonous plant?
Ans: Dicotyledonous plants are those plants that contain two cotyledons.