Anatomy of Root: Roots are cylindrical, underground non-green parts of the plant. It lacks nodes, leaves, buds but has endogenous lateral branches. The roots always grow towards gravity (geotropism) and away from the direction of light (phototropism). So, the roots are called positively geotropic and negatively phototropic. Generally, roots develop from the radical part of the developing embryo. The plants where the root formed by the radicle sustains are primary roots/tap roots seen in dicot plants.

The plants in which the primary roots degenerate and the fibre-like roots originate from the lower base of the stem is known as the fibrous root; it is present in monocots. Anatomically roots have epidermis, followed by the cortex, endodermis, pericycle, vascular bundle, and pith. Root has a radial vascular bundle with conjunctive tissue present in between the xylem and phloem. Let us now understand the tissue organization of roots of dicot and monocot plants.

Dicotyledonous Root

A dicot root has a tap root system, and it shows the following tissue arrangement:

a. Epidermis or Epiblema: It is the outermost layer of the root. It is usually single-layered. The outer wall of the epidermis has a unicellular tubular extension called root hairs which help in water and mineral absorption from the soil.

b. Cortex: From the epidermis to the endodermis, parenchymatous cells are found in several layers, which are known as the cortex. Cortex cells are thin-walled and loosely packed to allow the movement of water through them.

c. Endodermis: This is the innermost layer of the cortex, which is present between the cortex and the stele region. It is made by the single layer of the barrel-shaped cells possessing a special thickening of waxy suberin in the radial and tangential walls called casparian strip. Water molecules are unable to penetrate the casparian strip.

d. Pericycle: Next to the epidermis lies the pericycle, which consists of a thick-walled parenchymatous cell. It can be single-layered to several layered. It plays an important role in the secondary growth of dicot roots. In the dicot root, the cambium is absent but forms later as a ring-like structure known as the cambial ring. Parenchymatous cells of the pericycle become meristematic; they divide and join the cambial ring and become part of the vascular cambium and lateral roots.

e. Vascular Bundle: Xylem and phloem are at different radii; hence, a radial vascular bundle is present. Xylem present shows exarch condition with metaxylem lies in the centre and protoxylem is towards the periphery.

f. Conjunctive tissue: In between xylem and phloem, parenchymatous cells are present, called conjunctive tissue, which helps in the secondary growth of the root.

g. Pith: It is present in the centre. It is made up of a parenchymatous cell with intercellular spaces. Pith is not well developed in the root of dicots; it is small and inconspicuous in them.

Monocotyledonous Root

The anatomy of roots is quite similar to that of the dicot root, with some minor differences. The tissue organization of root can be explained as:

a. Epidermis: It is the outermost layer of the root, having a large number of unicellular root hair.
b. Cortex: It is made up of parenchymatous cells and is loosely arranged. The hypodermis is absent.
c. Endodermis: It is made up of barrel-shaped cells and does not possess a casparian strip.
d. Pericycle: It is a persistent layer that only gives rise to lateral roots as cambium is absent in monocots.
e. Vascular Bundle: Vascular bundle is a radial type. The vascular bundle does not possess vascular cambium, so the vascular bundle is closed and does not show secondary growth.
f. Conjunctive Tissue: The parenchymatous cells are present between the xylem and phloem, which comprise the conjunctive tissue.
g. Pith: Pith is large and well developed in the roots of the monocot plant.

Difference between Dicot and Monocot Root

Character	Dicot Root	Monocot Root
Pericycle	Give rise to lateral root, vascular cambium, and cork cambium.	Give rise to lateral roots.
Vascular bundle	Radial exarch vascular bundles vary from diarch to hexarch, i.e., vascular bundles are 2 to 6 in number.	Radial exarch vascular bundles with more than 6 vascular bundles (polyarch).
Cambium	Develops at the time of secondary growth.	Absent in monocots.
Pith	Small or absent.	Large and well developed.

Summary

Roots are the underground parts of plants, and they are positively geotropic and negatively phototropic. The main function of the root is to absorb water and mineral from root hairs. Roots generally have a single-layered epidermis with a unicellular tubular extension called root hairs. After the epidermis, we have multilayered cortex cells made up of parenchymatous cells. At the end of the cortex cells, there is a barrel-shaped endodermis that has a waxy covering that stops the flow of water. The Casparian strip is only present in the dicot root; it is absent in the monocot root. Roots have a radial vascular bundle with diarch to hexarch in dicot root and polyarch in monocot root. In the centre, they have a parenchymatous cell called pith, which is small and inconspicuous in dicot root and large and well developed in monocot root.

Frequently Asked Questions (FAQs) on Anatomy of Root

Q.1. What are the three types of roots?
Ans: The three types of roots in plants are tap root, fibrous root, and adventitious root.

Q.2. What is the shape of the endodermis cell?
Ans: The endodermis is made up of barrel-shaped cells.

Q.3. What kind of vascular bundle is present in the root?
Ans: Root has a radial vascular bundle with xylem and phloem present at alternate radii.

Q.4. Does monocot root show secondary growth?
Ans: No, monocot does not show secondary growth as they lack lateral meristem for secondary growth.

Q.5. What kind of pith is present in the dicot root?
Ans: Dicot root pith is small and inconspicuous.

Learn About Vascular Bundles Here

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