In this article we will discuss about the primary and secondary functions of roots.
Primary or Main Functions of Roots:
Roots take part in fixation of the plant and supporting the aerial shoot system.
2. Absorption of Water:
Roots absorb water from soil.
3. Absorption of Minerals:
Roots absorb mineral salts from soil.
4. Prevention of Soil Erosion:
Roots hold the soil particles firmly to prevent soil erosion.
They take part in transport of absorbed water and minerals to shoot system. Similarly, root has channels for the flow of organic food from aerial parts.
Many plants growing in aquatic habitats do not possess roots because there is little requirement for absorption of water and mineral salts, e.g., Wolffia, Utricularia, Myriophyllum, Ceratophyllum. In other aquatic plants roots develop only for balancing (e.g., Lemna, Pistia) and fixation (e.g., Hydrilla).
Secondary or Accessory Functions of Roots:
It occurs in fleshy roots.
Examples of fleshy tap roots are:
(i) Conical, e.g., Carrot
(ii) Fusiform, e.g., Radish
(iii) Napiform, e.g., Beet, Turnip and
(iv) Tuberous, e.g., Mirabilis.
Depending upon their shape and grouping, adventitious fleshy roots are of six types:
(a) Tuberous (root tubers), e.g., Sweet Potato
(b) Fasciculated, e.g., Asparagus, Dahlia
(c) Palmate, e.g., Orchis
(d) Nodulose, e.g., Curcuma
(e) Moniliform, e.g., Momordica
(f) Annuiated, e.g., Ipecac.
2. Extra or Mechanical Support:
It is provided by several types of roots:
(i) Buttress roots (plank roots), e.g., Bombax
(ii) Prop roots, e.g., Banyan, Rhizophora
(iii) Stilt roots, e.g., Maize, Sugarcane, Pandanus.
Roots help some of the weak stemmed plants to cling and hence climb up a support, e.g., Ivy, Tecoma, Betel, and Money Plant.
In many biennial and perennial plants e.g., Trichosanthes.
5. Nitrogen Fixation:
Nodulated roots of Pea, Bean, Gram, Methi, etc.
Prop roots, knee roots and pneumatophores of Mangrove plants, e.g., Rhizophora, Heritiera, Sonneratia.
By bearing adventitious buds on both tap roots (e.g., Dalbergia) and adventitious roots (e.g., Sweet Potato).
8. Hygroscopic Roots:
The roots absorb water from air, e.g., epiphytic roots, young prop roots of Banyan.
By storing air (e.g., Jussiaea = Ludwigia) some of the roots function as floats.
Free floating plants usually possess a cluster of adventitious roots from their nodes and bases to help in balancing the plants over the water surface, e.g., Lemna, Pistia, Eichhornia.
As in Trapa, Taeniophyllum, Tinospora, Podostemum.
12. Haustoria (Haustorial Roots):
They occur in some parasitic plants for absorption of food from the host, e.g., Cuscuta, Mistletoe.
The roots of several plants are associated with fungi to form mycorrhiza. Mycorrhiza helps the plant in absorption of phosphorus and nitrogen from organic sources and protects the plants from attack of pathogenic fungi.
14. Growth Regulators:
Roots synthesize certain growth regulations like cytokinins.