Types of Stems,Aerial stems,Reduced aerial stems,Erect aerial stems,Underground Stems,Weak aerial stems Excurrent, Delequescent, Caudex, Trailers

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Types of Stems

1. Aerial stems
(a) Reduced aerial stems
These stems are reduced and leaves appear to develop from tap root directly and form a rosette of small internodes e.g. Carrot, Radish, Turnip.

(b) Erect aerial stems
(i) Excurrent. These grow erect producing branches in acropetal order and plants assume a pyramidal shape e.g. Pinus, Eucalyptus and Polyathia.
(ii) Delequescent. The stem grow erect to some distance above the ground and there after branch profuse to form dome shaped appearance e.g. Mango, Banyan etc.

(iii) Caudex. The stem grows erect and do not produce any branches. They bear a cluster of leaves at the apex. e.g. Cocount, Plams.
(iv) Culm. These are erect stems which are unbranched and originate in clusters. Each such cluster is called culm. e.g. Bamboo, Wheat.
(c) Weak aerial stems
These are thin, delicate and slender and cannot stand erect. These need mechanical support to expose their leaves to the sun. They are of following types:
(i) Trailers. These weak stems after trailing for some distance lift its apex that bears flowers e.g. Euphorbia, Portulaca.

Weak Aerial Stems

A. Roots	D. Curved Petiole
B. Hoox	E. Flower
C. Tendril	F. Support G. Twiner

Prostrate	Decumbent
Diffuse

(ii) Prostrate. These weak stems lie horizontal on ground e.g. Oxalis.
(iii) Creepers /Runners. These creep on the ground with leaves arising at the nodes. From axillary buds new plants arises e.g. Strawberry, Hydrocotyle, Doob-grass.
(iv) Twiners. The weak stem of these plants have the habit of twining around supports without any special organs for attachment e.g. Bean, Abrus, Clitoria.
(v) Climbers. In this case stem clings with the help of special devices e.g. root climbers in Betel, sensive hooks in Artobotyrs, thorns or prickles as in Bougaivillea, the entire leaf in Jangli mattar. The terminal leaflets get

Weak Aerial Stems Contd

1. Runner
2. Stolon
3. Offset
4. Sucker

modified into tendrils in Sweet pea while in Gloriosa the leaf apex get transformed into tendrils.

(vi) Stolons. These develop from underground stems. They resemble runners except that they are produced just below the soil. e.g. Colocasia, Jasmine.
(vii) Offset. These are condensed runners. These arise as thickened branches in axil of lower leaves of main shoots. On breaking off from parent plant each branch forms an independent plant. e.g. Pistia and Water hyacinth.

2. Underground Stems
Some plants develop non-green, underground, perennial stems for the purpose of perennation and food storage. During unfavourable period the aerial plant dies but these stem survives. Under favourable period they give out aerial shoots. They differs from roots in
(a) presence of nodes and internodes.
(b) presence of scale leaves and adventitious roots.
(c) presence of axillary and terminal buds.
(d) presence of exogenous branches.

Types of underground stems are:
(i) Sucker. It is a modified underground runner and arises from underground axillary bud. It grows obliquely underground for sometime and then grows upwards e.g. Pondina (Mentha), Chrysanthemum etc.
(ii) Rhizome. It is stout, prostrate, underground stem provided with distinct nodes and internodes, scaly leaves at nodes, axillary as well as terminal buds. These buds favourable conditions give rise to aerial shoots which derive nourishment from them. e.g. Ginger, Alocasia, Turmeric, Ferns etc.
(iii) Tuber. These are swollen ends of underground branches which store food. It has distinct notches called eyes which represent nodes. Axillary buds are present which give rise to new shoots e.g. Potato (Solanum tuberosum).
(iv) Bulb. It is highly reduced and discoid under ground stem bearing a large number of scaly leaves. In the centre lies terminal bud which give rise to aerial flowering shoot. Stem is covered by numerous thickened overlapping leaves usually called scale. Some bulbs have dried scales called tunic for protection. Such bulbs of lily have small loosely arranged fleshy scale leaves without tunic. Such bulbs are called scaly bulbs or non-tunicated or naked.

Rhizome	Tuber
Bulb	Corm

(v) Corm. It is a condensed rhizome and has a short thick spherical underground stem which grow vertically. It has a large amount of stored food. It possesses nodes and internodes and scale leaves e.g. Amorphophallus, Colocasia.

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Anatomy of Flowering Plants Tissue and Meristematic Tissue Classification of Meristematic Tissue Apical Meristems of Stem and Root Permanent Tissue Simple Permanent Tissue Complex Tissues - Xylem Types of Xylum Complex Tissues - Phloem Classification of Permanent Tissue on Basis of Their Functions Types of Vascular Bundles Anatomy of Monocot Stem - Maize, Primary Structure of Stem Anatomy of Dicotyledonous Stem - Sunflower Stem Secondary Growth in Dicot System Origin and Activity of Cambium Origin and Activity of Cork Cambium Heart Wood and Sap Wood Primary Structure of Monocot Root Primary Structure of Dicot Root Secondary Growth in Dicot Roots Origin and Activity of Vascular Cambium Origin and Activity of Cork Cambiums Internal Structure of Dicot Leaf Internal Structure of Xerophytic Leaf Internal Structure of Monocot Leaf - Isobilateral Leaf

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