Roots
The plant organ which is of cylindrical shape and without chlorophyll growing towards the gravity is called root.
Types of Roots
There are two types of roots.
- a) Tap roots
- b) Adventitious roots
A. Tap Roots
The root arises from the seed directly is called tap root. The first root which is formed by the development of radicle is called primary tap root. It gives rise to secondary and tertiary roots. Deep feeder plants possess long tap roots while surface feeder plants have short tap root systems.
Tap roots are of further following types:
1. Fibrous Tap Root
The long and slender tap roots with slender branches are called fibrous tap root. In this type, roots are not thicker than the lateral branches. These types of roots are possessed by herbs like pea, bean, etc.
In leguminous plants, fibrous roots form root nodules. Bacteria live in these root nodules and fix atmospheric nitrogen. Bacteria provide the plant nitrates. In return, the plant provides bacteria-prepared food and protection. Thus, this is a symbiotic relationship.
2. Tuberous Tap Roots
The thick or swollen tap roots with reserve food are known as tuberous tap root. Such roots occur in biennial plants like carrot, turnip, radish, etc. The biennial plants live in two seasons. In the first season before winter, they store food in roots.
They use this food in the second season after winter. Tuberous roots may be
I. Conical
These roots are swollen towards upper end but taper towards the lower end. Examples include carrot and radish.
II. Fusiform
These tap roots are spindle shape i.e., swollen in the middle. Examples include English carrot.
III. Napiform
These tap roots are very much swollen above but abruptly tapers towards the lower end. Examples are turnip and beet.
B. Adventitious Roots
The roots arise from the stems or sometimes leaves are called adventitious roots. It has following forms:
A. Underground Adventitious Root
These roots arise from some part of the stem which is in contact with soil. They may be fibrous or tuberous.
- Fibrous adventitious roots:
These are long and slender roots that commonly develop on creeping and underground stems like grasses.
- Tuberous Adventitious roots:
These are swollen and fleshy roots. These roots contain stored food material. Examples are Asparagus, sweet potatoes. The number of roots swollen to form tuberous roots in sweet potato. These tuberous roots have stored food.
B. Partly Adventitious Root
These roots are partly above and partly below the ground. These roots may be slit roots, prop roots, and aerating roots.
I. Stilt Roots
In this case, adventitious roots arise from the lower portion of stem and grow into soil. They develop normally in soil. These roots fix the plant firmly in soil. They also absorb water and minerals. Such types of roots are found in corn, sugar cane, bamboo, etc.
II. Prop Roots
In this case, roots hang down in the air from the aerial branches of stem. These roots absorb moister of air. In some cases, these roots enter the soil. They also absorb water and mineral from the soil.
Ultimately, they form props. Props support the branches of plant. Props are also involved in vegetative propagation in some plants. Banyan tree, rubber tree, etc. are the examples.
1. Aerating roots:
These roots grow vertically upward and projects above the soil surface. These roots have openings for the entry of air. These are spongy in texture. Such roots are found in marshy plants like mangroves.
These roots absorb air from the surface for marshy plants. This air is used by roots for respiration.
2. Aerial Roots
These roots are entirely exposed in air. These roots perform special functions. There are two kinds of aerial roots.
3. Climbing Roots
These roots ae developed by stem in climbing plants. These roots firmly attach the plants with some support like wall tree trunk. These roots are very sensitive for touch. These roots secrete sticky fluid for attachment.
In some cases, they also develop disc like structures at their apices. These discs help them attach to the support firmly. Examples: These roots are developed in long pepper, etc.
4. Absorbing roots:
Some epiphytes develop long roots in the air for the absorption of moisture. These roots are called absorbing roots. These roots hang freely in the atmosphere. Such plants with absorbing roots are found in tropical rain forests.
Function of Roots
- Roots anchor the plant to the soil.
- They absorb water and minerals for plants.
- They store reserved food. Roots of turnip, radish, and carrot are used for storing food.
- Some roots are used for clinging. Its examples are props and haustoria.
- Some roots are used for vegetative growth. For example, the tuber of plants like sweet potato is used for vegetative reproduction.
- The roots of plants are involved in the absorption of moisture and oxygen from the air.
- The roots of leguminous plants develop nodules. Bacteria live in these nodules. They fix the atmospheric nitrogen and increase the fertility of the soil.