Root : Main axis of the plant body, mainly underground root, has the following parts—
Primary Root : Primary root is the descending organ of the plant that develops as the direct prolongation of the radicle of the embryo.
Root cap : The delicate root tip, covered by a group of corky dead cells, is called the root cap. It protects the root tip from being injured during penetration through the hard soil particles.
Normal Roots : All roots developing from the radicle, either directly from it or from its branches, are called normal roots.
Zones of a Root
(1) Root cap zone.
(2) Meristematic zone.
(3) Zone of cell elongation.
(4) Zone of root hairs.
(5) Zone of maturation.
General Characteristics of the Root
1. Root develops from the radicle of the embryo.
2. Root is positively geotropic.
3. Root is colourless due to the absence of chlorophyll.
4. Leaves and buds are absent.
5. Root generally grows downward into the soil.
6. Root cap is present over the apex to protect the internal tissue from damage.
7. The branches of the root arise from inner region, and are thus endogenous.
8. Root possesses root hairs which are always unicellular.
Tap Root : The root formed due to direct prolongation of radicle is called tap root, and it grows vertically. It goes perpendicularly into the soil.
Tap Root System : Tap root and the lateral roots taper towards their tips. These roots together form the tap root system of the plant.
Adventitious Root : Roots that grow from any part of the plant body other than radicle are called adventitious roots.
Fibrous Roots : In monocotyledons the radicle dies immediately after germination of seeds. Later on, a cluster of slender roots grow from the base of the stem. Such roots are called fibrous roots.
Fibrous Root System : The fibrous roots form the main root system of monocotyledons. It is known as fibrous root system or adventitious root system, e.g. rice, wheat, maize.
Functions of the root
(i) Root gives anchorage to the plant.
(ii) It provides water and minerals to the plant by asbsorbing them from soil.
Modified Roots
Modified roots carry some special functions. These functions may be mechanical or physiological. Modified roots are the following—
Fusiform Root : When the root is swollen in the middle and tapering gradually towards the apex and the base, it is called fusiform root, e.g. Radish (Raphanus sativus).
Napiform Root : When the root is swollen and spherical at the upper part and sharply tapering at the lower part, it is called napiform e.g. beet (Beta vulgaris).
Conical Root : When the root is broad at the base and gradually tapers towards the apex like a cone, it is called conical root, e.g. Carrot (Daucus carota).
Fasciculated Roots : Adventitious roots arise in bunches (fascicles) from lower nodes of stem and become thick and fleshy due to storage of food. These are called fasciculated roots, e.g. Dahlia, R. rellia and Asparagus.
Tuberous Root : A single adventitious root becomes tuberous, e.g. Sweet potato (Ipomoea batatas).
Nodulose Root : If the adventitious root becomes suddenly swollen at or near the apex, it is called nodulose root, e.g. Curcuma.
Moniliform or Beaded Root : When there are swellings in the adventitious roots at frequent intervals, they are called beaded or moniliform roots, e.g. Momordica.
Annulated Roots : When adventitious roots have a series of ring like swellings, they are called annulated roots, e.g. Psychotria (Ipecae).
Nodular roots : Plants of Leguminosae show spherical swellings on their roots, called bacterial nodules. They are inhabited by nitrogen-fixing bacteria-Rhizobium sp.
Epiphytic roots : Epiphytes have clinging roots to fix the plant on tree branches and velamen roots to absorb moisture from the air, e.g. Orchids.
Assimilatory roots or Photosynthetic roots : If the roots are green in colour and perform carbon assimilation, they are called assimilatory roots or photosynthetic roots. They carry out process of photosynthesis. Example Trapa.
Parasitic or Sucking Roots or Haustoria : Parasites develop certain kinds of roots which penetrate into the host plant and absorb food or water and minerals. These roots are called haustoria.
Some parasites absorb only water and minerals from the host and are able to synthesise their own food materials having green leaves. These are called partial parasites, e.g. Partial stem parasites: Loranthus Viscum.
Some parasites lack chlorophyll and depend on hosts for readymade organic food. They are called complete parasites.
Respiratory or Breathing roots or Pneumatophores : In some plants growing in saline marshes or fresh water, roots suffer from lack of oxygen. So surface roots produce some branches which grow against gravity and become aerial. They have small pores or special lenticels called pneumathodes through which air enters. These roots supply atmospheric air to the underground root system. These roots are called pneumatophores or respiratory or breathing roots, e.g. Avicennia.
Reproductive Roots : Roots of some plants develop vegetative buds. They develop into small plants and help in vegetative reproduction, e.g. Trichosanthes.
Balancing Roots : In free floating plants, each plant is provided with a well developed tuft of roots which act as balancing organs, e.g. Pistia, Eichhornia.
Prop Roots : Some plants have huge branches which spread sideways. A number of roots are produced from the branches. These roots grow vertically downwards and penetrate into the soil. They act as branch supporting pillars. Such roots are known as prop (support) roots, e.g. Banyan.
1. Stilt roots : In some plants roots develop from the basal nodes of the stem and grow obliquely. These roots are called ‘stilt roots’, e.g. Rhizophora, Pandanus.
Climbing roots : Plants with weak stems produce adventitious roots from the nodes or internodes. The secretions of these roots help in fixing the roots to the substratum. The climbing roots grow into the crevices of substratum to provide support to the climber, e.g. Pothos, Piper betle.
Buttress roots : Buttress roots are those which develop from the base of the main trunk. They give mechanical support to the plant, e.g. Terminalia and Bombax ceiba.
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