Modification of Stem

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Question – Potato is modified  –
A. Stem
B. Root
C. Leaf
D. None of these

My dear Aspirants, from the topic ‘modification of stems‘ You will see the above question in almost all competitive exams especially SSC and Rail exams. It is a part of the chapter ‘morphology of flowering plants’ of Biology. Here is the detail notes on ‘Modification of Stems’ with examples.

Modification of Stem
Modification of Stem

 

What is Modification of Stem?

♦ The stem is the main structural axes of a vascular plant that bears shoots, leaves, buds, nodes, internodes and the basal end-roots.

♦ It conducts water, minerals, and food to other parts of the plant body through various systems.

♦ In some plants, the stem is modified to perform different functions such as…
• Storage of food
• Support of plants
• Vegetative propagation
• Protection from animals
♦ These are simply known as modified stems and can be categorized into various classes.

Types of  Modification of Stems  with Examples

♦ Based on the type of modifications, stem modifications can be classified into the categories, They are ..

• Underground modifications
• Subaerial modifications
• Aerial modifications

◘ Let’s discuss all the three categories one by one ______

Underground Modification of Stem

◘ The Underground Stems of this type of plants modified for perennation and storage of foods.
◘ These plants produce aerial shoots annually.
◘ These underground stems looks like roots, but can be distinguished by the following characteristics.
• Stem of any plant must have a nodes and internodes.
• Presence of scale leaves, buds, and adventitious roots at the nodes.
• Internal structure resembles that  aerial stem and not of root.♦ Here are the some common types of underground modifications of stems ___ Tuber
➧  It is the branch of the main stem.
➧  Which accumulates or store food in it and swells up.
➧  The surface of the tuber contains many depressions like structures which are known as axillary buds or eyes.➧ These axillary buds capable of growing into new plants under favorable conditions.
➧ Example – Potato, Yam, Taro.

❒ Rhizome
➧  It is a branched, horizontally growing stem having nodes and internodes.
➧  The lower portion of the nodes gives rise to adventitious roots.
➧  On the node sessile scale leaves are formed which bear buds in their axil.
➧  These buds remain dormant, but on the ideal condition give to aerial shoots.
➧  Example – Turmeric, Ginger, Fingerroot, Galangal

❒ Corm
➧This is a spherical, branched vertically growing thick underground stem.
➧ Corm usually bears reduced internodes.
➧ Example – Crocus bulbs (Saffron), Amorphophallus, Gladiolus ❒ Bulb
➧ In bulb the stem is highly reduced disc- like structure.
➧ On this disc are present numerous fleshy scaly leaves covering a central terminal bud.
➧ Both the disc and scaly leaves collectively are called Bulb.
➧ Example – Onion, Garlic

Modification of Under ground Stem
Modification of Underground Stem

Sub Aerial Modification of Stem

♦ In Subaerial modifications, The stems are partially aerial and partially underground. Their general characteristics are___

• They have short aerial branches and adventitious roots develop at the nodes.
• The node of the stem can grow into a fully developed plant.
• Their sub aerial stem modifications are meant for vegetative propagation
• The plants are known as creepers.

◘ Here are the 4 types of sub-aerial modification of stems with examples.

❒ Runner
➧ It Grows prostrately on the surface of soil.
➧ Stem consists of long internodes.
➧ Example – Cynodon (Doob grass), Hydrocotyle, Oxalis (Wood sorrel)

❒ Stolon
➧ In some plants the nodes of horizontally growing underground stem give rise to branches which come out of the soil.
➧ The lower portion of the nodes gives rise to the roots.
➧ Example – Strawberry, Jasmine, Colocasia.

❒ Sucker
➧ Suckers are formed from the node of underground stem.
➧ Stem and sucker both grow horizontally under the soil.
➧ But sucker comes up obliquely in the form of leafy shoot.
➧ Roots formed from the lower portion of nodes.
➧ Example – Mint, Chrysanthemum.

❒ Offset
➧ Stem consists of thick and short internodes.
➧ The branches are formed from the main stem
➧ Each branch is capable of growing as an independent plant after separating from the parent plant
➧ Example – Eichhornia (water hyacinth), Pistia.

Sub Aerial modification of Stem
Sub Aerial modification of Stem

Aerial Modification of Stem

♦ In Aerial modification of stem the stem is modified to perform special functions like climbing, protection, food storage, vegetative propagation etc.

❒ Tendrils
➧ Axillary buds are modified into coiled, wiry thin structures called tendrils.
➧ tendrils help the plant to climb up
➧ Example – Passiflora (Passion flower), Vitis (Grapevine), Groundnut.

❒ Thorn
➧ In some plants, stem is modified into stiff, pointed unbranched or branched structure called Thorn
➧ Thorn performs a defensive function.
➧ Thorns are actually modified axillary buds or terminal buds and they possess vascular supply.
➧ Example – Bell, Lemon, Pomegranate, Ulex, Duranta, Carissa.

❒ Bulbils
➧ In some plants vegetative buds modify into a swollen structure called Bulbils.
➧ It separates from the parent plant and on the approach of favorable conditions give rise to a new plant.
➧ It is an organ of vegetative reproduction.
➧ Example – Yam, Oxalis

❒ Phylloclade
➧ The term “phylloclade” is derived from the Greek name phylloklados.
• Here phyllo means – leaf and
• Klados means – branch.

➧ Phylloclades are fleshy and flattened, photosynthetic shoots.
➧These are usually considered to be modified branches.
➧ In general, “phylloclade” refer to a portion of a leaf-like stem or branch with multiple nodes and internodes.
➧ The leaves transform to spine or scales.
➧ The transformed spine also helps in transpiration. Phylloclades take part.
➧ Example – Coccoloba, Euphorbia, Opuntia (Prickly pear)

❒ Cladode
➧ These are almost similar to Phylloclade with the difference that cladode may be made-up of only one Internode.
➧ These are green cylindrical or flattened leaf-like branch of limited growth.
➧ They help in photosynthesis.
➧ Example – Asparagus ( cladodes are one internode long ), Ruscus (cladodes are two internode long)

Aerial Modification of Stem


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