Biology Today — January 2018

Zone of differentiation/maturation

Cells in this region are differentiated into permanent

tissues (viz. xylem, phloem, pericycle, endodermis,

cortex, etc.) depending upon the functions they have

to perform. Root hairs are also present in this zone,

which help in water absorption.

Function : Increase the exposed surface of the root

for absorption.

Zone of cell elongation

It is present behind the meristematic zone. Cells of this

region have lost the power of division and elongate

rapidly thus, increasing the length of the root.

Function: External cells are responsible for

absorption of water and mineral salts from the soil.

Zone of cell formation or meristematic zone

It is subterminal in position and lies below the root

cap. It consists of compactly arranged small, thin

walled, isodiametric and meristematic cells having

dense protoplasm that are in active state of division.

Function : Produces new cells for root cap

and is essential for growth of root.

Zone of mature cells

Forms the bulk of root and consists of thick walled,

impermeable cells that do not undergo any change,

hence does not help in water absorption.

Function : Gives rise to lateral roots and anchors

the plant firmly in the soil.

Root cap

Cap-like parenchymatous, multicellular structure

which covers the root meristem. Its cells secrete

mucilage which lubricates the passage of root

through soil. These cells also possess starch

grains which take part in graviperception.

Function : It protects the root meristem

from friction of soil particles.

Root hair

Increases the exposed surface of the root for

absorption. New root hair appears in older

part of the zone of elongation in order to

absorb water from newer parts of soil.

Fig.: Zones of a typical root

Types of Root System

• There are three types of root system occurring in plants, i.e., tap root system, fibrous root system and adventitious root system.

Table: Comparison between different types of root system

Tap root system Fibrous root system Adventitious root system

(i) It is formed from the radicle of the

embryo.

It occurs in place of tap root system at the

base of main stem.

It may develop from any part of the plant

other than radicle or its branches.

(ii) It is always underground. It is always underground. It may be underground or aerial.

(iii) It consists of a single primary (main)

root.

Primary root is short lived. Instead

underground roots arise in groups from

base of stem.

Primary root is absent and it consists of

roots forming a cluster.

(iv) Primary root produces distinct

secondary roots, tertiary roots and

rootlets in acropetal succession.

The main roots are of equal lengths and

give off small branches. Main roots and

their branches are thin and thread like.

The roots may be thick, thin or variously

modified.

(v) It may be surface or deep feeder, the

deep feeder being the usual feature.

It is usually surface feeder. It is usually surface feeder.

(vi) It is commonly found in dicots. It is commonly found in monocots. It is found both in dicots and monocots.

Primary or tap root

Fig.: Tap root system

Secondary

root

Tertiary

root

Rootlets