Question – Potato is a modified _____:
D. None of these
My dear friends, you will come across the above question in almost all competitive exams, especially in SSC and Railway exams. The question belongs to the topic “Modification of Stem”. It is a part of the chapter “Morphology of Flowering Plants” in Biology. Here is a detailed note on ‘Modification of Stem’ with examples.
• 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.
Modification of Stem with Examples
• Based on the purpose and functions, stem modification can be classified into the following categories.
1. Underground modifications
2. Subaerial modifications
3. Aerial modifications
• Let’s discuss all three categories one by one ______
Underground modifications of Stem
• The Underground Stems of this type of plant are modified for perennation and storage of foods.
• These plants produce aerial shoots annually.
Perenniality is the ability of a plant to survive from one germination season to another under adverse conditions such as drought or winter.
• These underground stems look like roots, but can be distinguished by many characteristics.
• Stem of any plant must have nodes and internodes.
• Presence of scale leaves, buds, and adventitious roots at the nodes.
• Internal structure resembles that aerial stem and not of the root.
Here are some common types of underground modifications of stems ___
• It is the branch of the main stem.
• It accumulates or stores 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 are capable of growing into new plants under favorable conditions.
• Example – Potato, Yam, Taro.
• 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 that bear bud in their axil.
• These buds remain dormant, but in ideal condition to give to aerial shoots.
• Example – Turmeric, Ginger, Fingerroot, Galangal (Thailand Ginger)
• These are spherical, branched vertically growing thick underground stems.
• Corm usually bears reduced internodes.
• Example – Crocus bulbs (Saffron), Amorphophallus, Gladiolus
• In bulb the stem is a 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 Bulbs.
• Example – Onion, Garlic
Subaerial 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.
• It Grows prostrately on the surface of the soil.
• Stem consists of long internodes.
• Example – Cynodon (Doob grass), Hydrocotyle, Oxalis (Wood sorrel)
• In some plants the nodes of horizontally growing underground stem give rise to branches that come out of the soil.
• The lower portion of the nodes gives rise to the roots.
• Example – Strawberry, Jasmine, Colocasia.
• Suckers are formed from the node of the underground stem.
• Stem and sucker both grow horizontally under the soil.
• But sucker comes up obliquely in the form of the leafy shoot.
• Roots formed from the lower portion of nodes.
• Example – Mint, Chrysanthemum.
• 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.
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. Aerial modifications of stems are classified as follows.
• Axillary buds are modified into coiled, wiry thin structures called tendrils.
• Tendrils help the plant climb up
• Example – Passiflora (Passion flower), Vitis (Grapevine), Groundnut.
• In some plants, the stem is modified into a 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.
• 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 gives rise to a new plant.
• It is an organ of vegetative reproduction.
• Example – Yam, Oxalis
• 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 into spine or scales.
• The transformed spine also helps in transpiration. Phylloclades take part.
• Example – Coccoloba, Euphorbia, Opuntia (Prickly pear)
• 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 branches of limited growth.
• They help in photosynthesis.
• Example – Asparagus (cladodes are one Internode long), Ruscus (cladodes are two internodes long)
Modification of Stem with examples (Chart)
Frequently Asked Questions (FAQ)
Q1. Thorn of Citrus is modified:
Q2. Leaves are modified into tendrils in:
Q3. An example of an edible underground stem is:
Q4. New Banana plant developed from:
Q5. What type of stem modification is found in the Mint plant?
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