Roots and its modification

June 1, 2018

Introduction

Downward growing part of the vascular plant is called root.
Root can also be aerial or aerating, that is, growing up above the ground or especially above water.
Therefore, the root is best defined as the non-leaf, non-nodes bearing parts of the plant’s body.
On the germination of seed the first root arises from the radicle of the embryo. This is called the primary root.
There are various types of root. But, generally it is of two types. They are: Tap root and adventitious root.
Root has various functions. Some of them are:

Absorption of water and inorganic nutrients.
Anchoring of the plant body to the ground, and supporting it.
Storage of food and nutrients.
Translocation of water and minerals to the stem.
In response to the concentration of nutrients, roots also synthesize cytokinin, which acts as a signal as to how fast the shoots can grow.

Modification of roots:

The normal type of root is modified variously to perform many functions.
This helps the plant to survive in surrounding environment which is known as the modification of root.

A) Modification of Tap root

It is the normal tap root modified to store the food material.
It changes its shape and size due to accumulation of food materials.
According to their shape, they are classified into following types:

1) Fusiform root

It is spindle shaped root with middle part swollen and gradually tapering towards the both ends.
e.g., Radish.

2) Napiform root

The upper part of the root becomes almost globular due to maximum swelling.
It tapers sharply towards the lower ends.
e.g., Turnip, Beet root.

3) Conical root

Broad at the base and gradually tapers towards the apex like a cone.
e.g., Carrot.

4) Tuberous

Thick and fleshy root with a definite shape.
e.g., 4 O’ clock plant.

Image source: quora

B) Modifications of Adventitious root

They are modified to perform various functions such as storage of food, support, assimilation and other important functions.

1) For storage of food

a) Tuberous root

This is a swollen root without any definite shape.
It appears singly.
e.g., Ipomoea.

b) Annulated root

Root modified to form a series of ring-like swelling or annuli on its body.
e.g., Ipecacuanha.

c) Nodulated root

Root becomes suddenly swollen at or near the apex.
e.g., mango, ginger.

d) Fasciculated root

Several roots appear in cluster at the base of the stem.
e.g., Dahlia, Asparagus, etc.

e) Moniliform or Beaded

Roots swell at regular intervals giving a beaded appearance.
e.g., Momordica, Portulaca, Indian Spinach, etc.

2) For mechanical support

a) Prop root

These are the roots arising from the main stem and branches of a tree.
They grow vertically or obliquely downwards to the soil.
They provide support to the plant body.
Look like pillars and allow tree to grow in large area.
e.g., Banyan tree.

Image source: learninsta

b) Stilt root

The lower nodes above the ground level give rise to a ring of stout and slender roots; stilt roots.
They grow obliquely downwards into the soil and give support to the stem.
e.g., Maize, Sugarcane, Pandanus.

c) Climbing root

Roots developing from the nodes and internodes of the many tropical climbers is known as climbing roots.
They attach themselves to any support and help in climbing.
e.g., Piper betel, P. longum, etc.

3) For vital functions

a) Haustorium or sucking root

Parasitic plants develop a peg-like structure known as haustoria.
The haustoria penetrate the living host tissue and absorb food by sucking.
They have no root cap.
e.g., Cuscuta.

b) Epiphytic root

Epiphytic plant develops a special kind of aerial roots.
These roots contain spongy tissue called velamen.
The cells of velamen are dead and empty, which help in absorption of moisture from the air.
e.g., Orchid.

c) Respiratory root or Pneumatophores

Some plants growing in marshy places and salt lakes produce special roots which grow vertically upward from the underground roots.
They usually develop above the level of water around the trunk of the tree.
They have numerous aerating pores that help in respiration.
e.g., Jussiaea, Rhizophora, etc.

d) Assimilatory roots

Long slender hanging root develop from the branches in some plants.
They contain chlorophyll and carry out photosynthesis.
e.g., Trapa, Tinospora, etc.

e) Floating root

Spongy roots of some hydrophytic plants are known as floating roots.
They store air and help in buoyancy.
e.g., Pistea, Jussiaea, etc.

f) Mycorrhizal root

It is found in gymnosperms.
The younger portions of the tap root become closely invested by the hyphae of a fungus.
They lead symbiotic life, as the fungus helps in absorbing minerals and water and in turn the plant root provides the organic food.
e.g., roots of Pinus, Cycas, etc.