The cylindrical plane organ without chlorophyll, growing towards the gravity is called root.
Roots have following morphological characters
Kinds of Roots
There are two groups of roots: Tap root and Adventitious roots.
(a) Tap root
The root directly arises from the seed is called tap root. The first root which is formed by the elongation of radical is called primary tap root. It gives rise to secondary and tertiary roots. The deep feeder plants have a long net work of tap root system. The surface feeder plants have short tap roots. There are following forms of tap roots:
I. Fibrous tap roots: The long and slender tap root with slender branches is called fibrous tap root. It is found in many herbs like bean, pea etc. In some leguminous plants, the tap roots form nodules. Bacteria live in these nodules and fix atmospheric nitrogen.
2. Tuberous tap roots: The thick or swollen tap roots with reserve food are known as tuberous tap roots. Such roots occur in biennial plants like carrot, turnip, radish etc. The biennial plants live in two seasons. In first season (before winter) they store food in the roots. They use this food in the second season (after winter). Tuberous roots may be:
Conical: These roots are swollen towards tipper end but taper towards the lower end. Examples: carrot, radish.
Fusiform: These tap roots are spindle shape i.e. swollen in the middle. Examples: English carrot
Napiform: These tap roots are very much swollen above but abruptly tapers towards the lower end. Examples: turnip and beet.
(b) Adventitious roots
The roots arised from the stems or sometimes leaves are called
adventitious roots. It has following forms:.
1. Underground or subterranean adventitious roots: These roots arise from some part of stem which is in contact with the soil. They may be fibrous or tuberous.
Fibrous adventitious roots: These are long and slender roots. These commonly develop on creeping and underground sterns like grasses.
Tuberous adventitious roots: These are swollen and fleshy roots. These roots contain stored food material. Examples: Asparagus, sweet potato
2. Partly subterranean adventitious roots: These roots are partly above and partly below the ground. These roots may be stilt roots, prop roots and aerating roots.
(a)Stilt roots: In this case, adventitious roots arise from the lower portion of stem and grow into soil. Such types of roots are found in corn, stig:if cane, bamboo etc.
(b)Prop roots: In thiF case, roots hangs down in the air from the aerial branches of stern. These roots absorb moister of air. Example:bayan rubber tree etc.
(c)Aerating roots or pneumatophores: These roots grow vertically upward and projects above the soil surface. These roots have openings kir the entry of air. Such roots are
Aerial roots: These roots are entirely exposed in air. These roots perform special functions. There are two kinds of aerial roots.
a.Climbing roots: These roots are developed by stein in climbing plants. These roots firmly attach the plants with some support like wall, tree trunk. These roots secrete sticky fluid for attachment. Examples: These roots are developed in long pepper etc.
b.Absorbing roots: Some epiphytes develop long roots in air for absorption of moisture. These roots are called absorbing roots. These roots hang freely in the atmosphere. These roots are develved in orchids.
4. Parasitic roots or Haustoria: These roots are developed in
parasitic plants like Cuscut Stem develops these roots for absorption of food from host. These roots penetrate into the host tissues.
5. Aquatic roots: These roots are developed in water plants. These roots arise form stem and spread in water. Example: Hydrilla.
Fig: Aquatic roots