Root System

Root is the descending portion of the axis of the plant. It is not normally green in colour. It is characterised by the absence of nodes and internodes.

There are two types of root systems, the tap root system (seen in dicots) and fibrous root system (seen in monocots).

Tap Root System

In dicots the radicle elongates into the primary root which grows downwards into the soil and bears smaller roots as its branches. The primary root grows and becomes the main root or the tap root. The tap root, along with its branches, constitutes the tap root system of a plant. As the primary root elongates, it goes on producing lateral branches called secondary roots. These in turn produce tertiary roots, which grow in various directions fixing the plant firmly into the soil.

fig. 27.2 - Tap Root System

Adventitious Root System

Roots developing from any part of the plant body other than the radicle are called adventitious roots. They may arise from the leaves as in Bryophyllum or from the branches as seen in Banyan.

In monocotyledons, the primary root from the radicle later disorganizes and a cluster of adventitious roots arise from the basal portion of the stem. They are of uniform thickness and length. In grasses and some herbaceous monocots, they look like tufts of fibres and are called fibrous roots. Fibrous roots are also adventitious.

fig. 27.3 - Fibrous Root System of Grass

Regions of the Root

The root consists of the following regions from the apex upwards:

Root Cap Region

The tip of a root is covered by a small cap-like protective structure, the root cap. It consists of dead cells.

Region of Cell Division

Just behind the root cap, there is a meristematic zone in which the cells are in a state of active division. The root cap protects the young delicate zone against mechanical injury from contact with hard soil particles.

Region of Elongation

This region lies above the region of cell division. The cells located in this region undergo elongation and enlargement and are responsible for increase in length of the root.

Region of Maturation

The cells located in this region later differentiate into various types of tissues. Externally, this region produces a cluster of very fine and delicate thread-like structures known as root hairs. These root hairs take part in the absorption of water and mineral salts from the soil.

fig. 27.4 - Regions of the Root

Functions of Roots

Normal Functions

1. The root system helps in fixing the plant firmly in the soil.

2. Root hairs help in absorbing the water and mineral salts from the soil.

3. Roots conduct water and salts absorbed by root hairs to the aerial parts.

Special Functions

In some plants, the roots undergo modification to perform special functions, such as storage and respiration.