Modification of Stem

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In most of the plants the stem is aerial vertically upward and bears leaves and flowers and fruits. However some stems are modified into various shapes to carry on special functions, such as perennation, vegetative propagation and synthesis and storage of food etc. Stems are variously modified into underground, sub aerial and aerial stems.

Underground Modified Stem

Underground stems have presence of nodes and internodes, scale leaves and adventitious roots arising from the nodes and presence of axillary and terminal buds. Functions: store reserve food, and are adapted for perennation and during favorable conditions underground stems give rise to aerial shoots, with the onset of unfavourable conditions the aerial shoots die.

Table Showing Underground Modifications of Stem.

Types

Characters

Examples

Rhizome

Thick, fleshy, prostrate, flattened horizontally growing stem near the soil surface. Bears scale leaves and branches on nodes, terminal and axillary buds, adventitious roots

Ginger (Adrak),

Turmeric (Haldi)

Corn

Small, rhizome like, scale leaves bears, nodes and internodes, buds and adventitious roots

Saffron (kesar), Yam (jimikand), Gladiolus

Bulb

Reduced stem, flattened discoid stem with crowded nodes bearing overlapping fleshy (inner) and dry (outer) scale leaves. Terminal bud forms foliage leaves. Adventitious roots grow from discoid base

Onion (Allium cepa)

Tuber

Swollen tip of the underground branch, stores large amount of reserve materials primarily starch, bear ‘eyes’. Each eye is a node which bears bud and scar of scale leaves

Potato

Sub-Aerial Modifications of Stem

In sub-aerial modifications some parts of the stem lives underground whereas remaining part of stem is aerial, herbaceous plants with a thin, delicate and weak stem. Plants bear adventitious roots and aerial branches at their nodes function as vegetative propagation.

Table Showing Sub-Aerial Modifications of Stem.

Type

Characters

Examples

Runner

Slender stem, weak, slender, branch with long, thin internodes, runs horizontally on soil surface giving off adventitious roots at nodes

Grass, Oxalis

Stolon

Slender lateral branch that arises from the base of the main axis, branch arches downwards to touch the ground, where its terminal bud gives rise to a new shoot and roots

Jasmine, Mint (Pudina)

Offset

Stout and short runner like branch, which bands at the tip and gives rise to a rosette of leaves above and roots below

Water hyacinth, water lettuce

Sucker

Originates from the basal and underground portion of the main stem, shorter and stouter than runner, grow horizontally for a distance partly below the ground

Chrysanthemum