Q.Define Root modification. Explain how root is modified to perform different functions ?
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Start your 14-day free trial to unlock the full solution →Root modification = change in root form to perform special functions. Main types: storage (fusiform/conical/napiform tap roots; tuberous, fasciculated adventitious roots), mechanical support (prop, stilt, climbing roots), respiration (pneumatophores), nitrogen fixation (root nodules), and special vital functions (assimilatory, epiphytic, parasitic, reproductive, floating).
Root modification is the permanent change in the shape, structure and function of a root so that, apart from its normal jobs of fixation and absorption of water and minerals, it performs some additional special function. This is an 8-mark topic in the NCERT/CBSE-aligned TS Intermediate morphology-of-flowering-plants unit; the main kinds are described below.
A. Modifications of the TAP ROOT
1. For storage of food — the root becomes swollen (fleshy) with stored food:
- Fusiform — swollen in the middle, tapering at both ends, e.g. radish.
- Conical — broad at the top and tapering below like a cone, e.g. carrot.
- Napiform — almost spherical (top-shaped), sharply tapering below, e.g. turnip, beet.
- Tuberous (tuberised) — swollen irregularly, no definite shape, e.g. Mirabilis (four-o'clock).
2. For respiration (pneumatophores) — in mangrove plants (e.g. Rhizophora, Avicennia) growing in marshy, oxygen-poor soil, some roots grow vertically upward out of the mud and bear tiny pores (pneumathodes) through which the plant breathes. These are called pneumatophores or breathing roots.
3. For nitrogen fixation (nodulated roots) — in legumes (Fabaceae) the roots bear small swellings called root nodules housing Rhizobium bacteria that fix atmospheric nitrogen into a usable form.
B. Modifications of ADVENTITIOUS ROOTS
1. For storage of food:
- Tuberous roots — single swollen roots, e.g. sweet potato (Ipomoea).
- Fasciculated roots — a cluster of swollen roots at the stem base, e.g. Dahlia, Asparagus.
- Nodulose / moniliform / annulated — beaded or ringed swollen roots (e.g. Vitis, ginger-like forms).
2. For mechanical support:
- Prop (pillar) roots — hang down from branches, enter the soil and become thick pillars supporting the huge crown, e.g. banyan.
- Stilt roots — short, thick roots arising from the lower nodes and entering the soil obliquely to give extra support, e.g. maize, sugarcane, Pandanus.
- Climbing (clinging) roots — arise from nodes and help the plant climb by clinging to a support, e.g. money plant (Pothos), betel.
3. For special vital functions:
- Assimilatory roots — become green and photosynthesise, e.g. Tinospora, Trapa. …
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