Root | Definition, Types, Examples, Morphology, & Functions
Roots are cylindrical, underground and non-green part of the plant. It is generally the descending portion of the plant axis i.e., it grows downward into the soil. It lacks nodes, leaves, buds but gives rise to endogenous lateral branches. Roots move in the direction of gravity (geotropism) and against the direction of light (phototropism). Hence, the roots are said to be positively geotropic and negatively phototropic.
Plants have well developed root systems. The main root and its lateral branches form the root system. There are three types of root system.
(i) Tap root system: The primary root is directly elongated from the radicle and grows inside the soil (e.g. dicots). It bears lateral roots of several orders that are referred to as secondary, tertiary roots etc. The primary roots and its branches constitute the tap root system.
(ii) Fibrous root system : In monocotyledonous plants, the primary root is short-lived and is generally replaced by a number of fine fibrous roots. These roots originate from base of the stem and constitute the fibrous root system as seen in wheat plant.
(iii) Adventitious root system : Some plants have specialised roots called adventitious roots. These roots develop from any parts of the plant other than the radicle e.g., Grass, Monstera, Banyan tree.
Main Functions of Root
- Absorption of water and minerals from the soil.
- Provide anchorage to the plant parts.
- Storage of reserve food material.
- Synthesis of plant growth regulators.
Regions of the Root
(i) Root cap : The apex of the root is covered by a thimble-like, structure called root cap. It is multicellular and is made up of parenchymatous cells. It protects the tender apex of the root as it makes its way through the soil.
(ii) Region of Meristematic Activity : This layer is few millimetre above the root cap. The cells of are thin-walled, small, with dense protoplasm. They divide repeatedly to produce new cells.
(iii) Region of elongation : The cells proximal to the meristematic region undergo rapid elongation and enlargement and are responsible for the growth of roots in length.
(iv) Region of maturation : The cells elongation zone gradually differentiate and mature. Hence, this zone proximal to region of elongation, is called the region of maturation.
Some epidermal cells from the region of maturation form very fine and delicate thread-like structures called root hair. The root hair increases the surface area for absorption of water and minerals from the soil.
Modifications of Root
The roots are mainly involved in absorption of water and minerals from the soil. Roots in some plants undergo modifications in their shape and structure in order to perform functions like respiration, storage and protection.
(i) Storage roots : In some plants the primary tap root is modifiedto store food and assumes various shapes. e.g., tap root of carrot, turnip, radish, beet and adventitious roots of sweet potato get swollen and store food.
(ii) Respiratory roots : In some plants such as Rhizophora growing in swampy areas, many roots come out of the ground vertically upwards to get oxygen for respiration. Such roots are called pneumatophores.
(iii) Prop roots : They arise from the branches of stem for providing mechanical support to heavy branches, as pillars e.g., banyan tree
(iv) Stilt roots : They arise from lower nodes of stem to support main axis and enter the soil obliquely e.g., Sugarcane, maize.
|Adventitious root with special functions :
(i) Floating roots: In aquatic plants (e.g., Jussiaea) white spongy roots arise from branches and help in floating and respiration.
(ii) Assimilatory roots: The aerial roots of Tinospora and submerged roots of Trapa (Water chestnut) become green and synthesize food. Podostemon also has green assimilatory roots.
(iii) Sucking or haustorial roots: These roots suck food and water from host and are found in parasitic plants e.g., Cuscuta, Orobanche, Viscum.
(iv) Hygroscopic roots: These are found in epiphytes, specifically orchids and help in absorption of moisture from the atmosphere using special tissue called velamen.
(v) Contractile roots: They shrink 60-70% of the original length and bring underground organs at proper depth in the soil e.g., corm of Crocus (saffron), Freesia.
(vi) Root thorns: These are hard, thick and pointed thorns e.g., Pothos armatus and Acanthorhiza.
(vii) Clinging roots: These are non absorptive adventitious roots arising either from nodes (e.g., Tecoma. betel), internodes (Ficus pumila) or both (e.g., juvenile stage of vy).
(viii) Reproductive roots: These are fleshy, adventitious roots used for vegetative reproduction e.g. sweet potato (lpomoea batatas), Dahlia.
(ix) Leaf roots: In Salvinia, one leaf of each node modifies into root like structure for balancing the plant in water.
(x) Epiphyllous roots: These roots arise from the margins of leaf lamina for vegetative reproduction e.g., Bryophylum.