In this article we will discuss about the Root of a Plant:- 1. Meaning of Root 2. Modifications of Root.
Meaning of Root:
Generally, root is said to be the part of a plant which remains inside the soil. But there are subaerial as well as aerial roots also. Actually, root is a positively geotropic part of the plant having a root cap and many unicellular root hairs. Ontogenically the root arises from the radicle.
(i) Tap root:
The primary root with its many small lateral branches, which are normally meant to absorb the water from the tap root system.
(ii) Adventitious root:
A root that grows from any part of the plant like stem, leaves etc. but not from the radicle, is called adventitious root.
Modifications of Root:
(A) Tap Root Modifications:
1. Fusiform root:
When root is thickened in the middle and tapering at the ends, e.g., Raphanus sativus (radish).
2. Napiform root:
When root is almost spherical at one end and tapering sharply at the other end, e.g., Brassica rapa (turnip).
3. Conical root:
Root which appears like a cone, i.e., broad at the base and tapering gradually into a pointed end, e.g., Daucas carota (carrot or Gazar).
4. Tubercular root:
When root is thick, fleshy and of irregular shape. It may be a modification of tap root, e.g., Mirabilis jalapa (Four O’clock plant), or of adventitious root, e.g., Ipomoea batatas (sweet potato).
(B) Adventitious and Fibrous Root Modifications:
1. Fasciculated root:
Modified adventitious root in which many tubercular roots are present in clusters on the stem, e.g., Asparagus, Dahlia, etc.
2. Moniliform root:
When many swellings occur in root at certain intervals providing the beaded shape to the root, it is said to be moniliform, e.g., Momordica.
3. Annulated root:
When series of round swellings are present in the root, it is called annulated, e.g., Cephaelis ipecacunha.
4. Epiphytic roots:
These are the aerial roots of the epiphytic plant like Vanda, which internally contain a spongy tissue called velamen. The velamen helps in the absorption of moisture from air.
5. Clasping or climbing roots:
These develop on the nodes of weak – stemmed plants like, Pothos, Hedera, etc., and help the plant to climb and fix on the wall or other parts.
6. Prop roots:
From the branches of some big trees develop roots growing vertically downward. They enter in the soil and provide support to the plant, e.g., Ficus benghalensis.
7. Leaf roots:
They develop on the margin of leaves from the adventitious buds, e.g., Bryophyllum.
8. Contractile roots:
Unbranched roots, developed with underground stems like corm, rhizome, bulb, etc. These roots lack root hair, e.g. Crocus, Typhonium, etc.
9. Respiratory roots or pneumatophores:
They develop from the underground roots towards the upper side and come out near the plant in the form of conical spikes. Many pores are present on their upper part for respiration. These are common in plants near marshy places and salty lakes, e.g., Rhizophora.
10. Sucking roots or haustoria:
The roots which develop in parasitic plants for sucking the food material from the host with their special organs, like haustoria, e.g., Cuscuta, Loranthus, Viscum, etc.
11. Assimilatory roots:
Green, chlorophyll- containing roots of plants like Trapa natans, Tinospora etc. are called assimilatory roots.
12. Mycorrhizal root:
It shows the symbiotic relationship between the roots of the plant and fungal hyphae, e.g., Monotropa, Morus, etc.