Root Modifications

The root is an underground part of the plant that absorbs water and minerals from the soil and anchors the plant firmly.

In some plants, the roots change their shape and get modified to absorb and transport water and minerals from the soil to different parts of the plant. They are also modified for support, food storage, and respiration.

The root modifications perform two major functions- Physiological and Mechanical.

Let us have a detailed look at the modification of roots.

Modifications of Tap Roots

For Food Storage

In some plants, the roots become fleshy due to the absorption of food material. The aerial parts of these plants are worn out due to unfavourable conditions. When the conditions are favourable again new buds emerge either from the fleshy root or from a small bit of stem above.

For eg., the taproots of carrot and turnip get swollen to store food.

Depending upon their shapes, they are classified as;

• Conical roots are broad at the base and conical at the apex, eg., carrot

• Fusiform roots are swollen in the middle and tapering towards both the ends, eg., radish

• Napiform roots are spherical at the base and taper towards the apex, eg., turnip

• Tuberous roots have no specific shape. They appear thick and fleshy, eg., sweet potato

For better Respiration

In some halophytes such as Rhizophora that grow in swampy areas, the roots emerge out of the ground and grow upwards to get oxygen for respiration. The root tips of these plants have minute pores called lenticels through which they respire.

Nodulated Roots

Roots of the leguminous plants are modified into root nodules which contain nitrogen-fixing bacteria such as Rhizobium. They help in fixing the atmospheric nitrogen into nitrates and make it available to the plant.

Modification of Adventitious Roots

For Food Storage

Adventitious roots are modified into:

• Simple Tuberous Roots are swollen and do not assume any shape. For eg., sweet potato

• Nodulose Roots are single beads. They become swollen at the apex and have a definite shape, eg., ginger

• Fasciculated Tuberous Roots is the cluster of adventitious roots for food storage. They have a definite shape, eg., Dahlia

• Moniliform Roots are swollen and constricted, eg., grasses

• Annulated Roots has an appearance of discs placed one over the other, eg., Ipecac.

For Support

• Prop Roots: These roots develop from the branches of the tree, hang downwards, and penetrate into the ground thereby supporting the tree. Eg., roots of the banyan tree.

• Stilt Roots: These roots grow obliquely from the basal node of the stem. Eg., roots of the sugarcane.

• Climbing Roots: These roots arise from the nodes and attach themselves to some support to climb over it. Thus, they provide support to the plant. Eg., Money plant

• Clinging Roots: These roots enter the crevices of some support and fix the plant. Eg., epiphytes orchids

• Buttress Roots: These are vertically elongated basal part of the stem which spread in different directions in the soil. These are horizontally compressed and appear like planks. Eg., Bombax.

For Special Functions

• Epiphytic Roots: These roots are aerial, hanging and spongy. They have a porous wall and absorb moisture from the atmosphere. These aerial roots possess a special sponge-like tissue known as velamen. Velamen absorbs and stores moisture from the air since these plants do not have direct contact with the soil.

• Sucking Roots: These are microscopic, developed by the roots to absorb nutrients from the host. These are also known as parasitic roots or haustoria because these are found in non-green parasitic plants. These roots arise from the nodes and penetrate into the host tissue. They then enter into the conducting tissue from where they obtain the required food material.

• Floating Roots: These arise from the nodes of the aquatic plants and help in floating and respiration. Eg., Jussiaea. These roots are very spongy in nature and look like a mass of white cotton. The plant floats due to its buoyancy. They dry when taken out of the water.

• Assimilatory Roots: These are also known as photosynthetic roots. These, when exposed to the sun, develop chlorophyll and manufacture food. Eg., In Tinospora, the roots hang as green threads from the nodes during the rainy season. They assimilate carbon dioxide in the presence of sunlight.

• Mycorrhizal Roots: The symbiotic association of a fungus with higher plants is called mycorrhizal root. The fungus absorbs nutrients from the soil for the plant, and the plant, in turn, provides organic food to it. Eg., Pinus

• Reproductive Roots: In some plants such as sweet potato, the adventitious roots give rise to buds which develop into leafy shoots. Root cuttings are the main mode of reproduction.

Thus we see how roots modify themselves according to the functions they perform.

(58)