Plant Stem | Stem types | Modification of Stem

in this article we are to discuss about what is plant steam? plant stem types? plant stem bud? what is a stem of a tree?


The aerial part of the plant is known as shoot. It is the stem, its branches and the leaves. consists of the stem develops from epicotyl (part of the shoot system the embryonal axis of the seed) stem forms the main skeleton of the Stem differs from roots in many features shoot. 

Characteristics of Stem 

(1) Stem is the ascending part of the plant axis developing from the plumule (or tigellum). 

(2) Normally, the stem growS away from the gravity (i.e., negatively geotropic) but positively light (i.e.towards Jussiae phototropic). 

(3) Stem is differentiated into nodes and internodes. It bears leaves and branches at the nodes. 

(4) The shoot (stem and its branches) is usually green and photosynthetic. 

(5) Trichomes (or hairs) present on the stem are either unicellular or multicellular. 

(6) Stem apex is always apical (sub-apical) in root due to the presence of root cap). 


A bud is a condensed young shoot with underdeveloped leaves. In a bud, internodes are short, hence, nodes are situated very close to one another and the leaves become crowded. 

There are three types of buds-  

(I) vegetative 

(ii) floral and  

(ii) modified  

(I) Vegetative buds 

These buds develop into a vegetative shoot. Vegetative buds are further classified into following three sub-types. 

1. Normal buds. Such buds are present at the tip of the branches and the main axis, and are called terminal or apical buds. They also occur in the axil of the leaves and are called axillary or lateral buds . 

2. Accessory buds. Some plants regularly produce a few additional buds by the side of axillary buds. These are called accessory buds or supernumerary buds. 

3. Adventitious buds. These are the buds which develop from any part of the plant body other than those of normal and accessory buds. 

These could be of the following types: 

(a) Cauline buds. These buds arise directly from the stem; e.g., rose. 

(b) Radical buds. These buds develop on the roots; e.g. sweet potato, Ipecac, Dalbergia 

(c) Foliar buds. These are the buds which develop on the leaves; e.g., Bryophyllum (sprout leaf plant), Begonia (elephant ear plant), Kalanchoe, etc. 

[II] Floral buds 

These buds always develop into flowers. 

[III] Modified buds 

Both vegetative and floral buds, may be modified into different structures for some specialised functions. These are follows. 

1. Modifications of vegetative buds. 

Vegetative buds may become modified into following structures 

(a) Tendrils. Examples: passiflora (passion flower), Vine, etc. 

(b) Thorns Examples: Citrus (lemon),Duranta, Cariss (karonda), etc. 

(c) Bulbils These special reproductive structures are  found in Dioscorea (yam), etc. 

2. Modifications of floral buds. Following are some of the structures into which floral buds are get modified: 

(a) Tendrils. Examples: Cardiospermum (balloon vine), sandwich island climber, etc. 

(b) Bulbils. These special reproductive bodies occur in Allium sativum (garlic), Chlorophytum, etc. 

Size of Stem 

Depending upon the size and woodiness of stems, plants can be classified into herbs, shrubs and trees. 

1. Herbs. These are plants with small and soft stems. They are either unbranched or have only a few branches.These include Brassica (mustard), Triticum vulgare (wheat), Raphanus sativus (radish),Zingiber officinale (ginger), etc. 

2. Shrubs. These are medium sized, perennial plants with profusely branched woody stem. The branches arise from the base of stem and the plant attains a bushy appearance; e.g., Hibiscus rosa-sinensis (shoe flower), Camellia sinensis (tea). 

3. Trees. These are perennial plants with hard woody stem. They have a long trunk (the lower unbranched part of trees) and the branches arise from the upper part of the stem; e.g., Mangifera indica (mango), Dalbergia sissoo (shisham), Meliaazadirachta (margosa), etc.  

Forms of Stem 

Basically, stem is the aerial part of the plant axis. in some plants, however, it becomes underground to carry out some specific functions. Aerial stems can be grouped into following two types on the basis of their form. 

[I] Strong stem  

Plants like mango, margosa, cucalyptus, mustard,etc., have erect stems which keep the plants in 

upright position. The following terms are important in relation to strong stems. 

1. Excurrent. The main axis continues growth and the lateral branches develop regularly giving a conical appearance to the tree eg, Polyalthia longifolia, Casuarina,lateral growth of 

2. Deliquescent. The branches is more vigorous than that of main axis. As a result, the tree assumes a round or spreading appearance; e.g. Mangifera indica, Delonix regia, etc. 

3. Caudex 

It is an unbranched, stout and cylindrical stem, marked with scars of fallen leaves (Fig. 13C); e.g., Cocos nucifera, palms, etc. 

4. Culm. It is a jointed stem with solid internodes nodes and hollow e.g., Bambusa arundinacea (bamboo), Triticum vulgare (wheat). 

[II] Weak stems 

These stems can not maintain an upright position. 

On the basis of their habit, weak stems can be divided into following categories. 

1. Trailing. It is a weak stem that spreads over the surface of the ground without rooting at 

the nodes. These fall into three categories: 

(a) Prostrate (Procumbent). A stem that lies flat on the ground; e.g., Portulaca 

(b) Decumbent. A stem that lies flat but its apex is raised; e.g., Tridax. 

(c) Diffuse, A trailing stem with spreading branches, e.g., Boerhaavia. 

2. Creeping. The plant grows horizontally on the ground and gives off roots at each node, e.g, 

grasses. Runners, stolons, offset and suckers are also creeping stems. 

3. Climbing. 

This weak stem climbs a support by means of some special structure. Depending upon the structures used for climbing, these are divided into following types: 

(a) Stem climbers or twiners. weak, long and slender stem that climbs by twining its body around the support; e.g., Cuscua Clitoria ternatea  

(b) Lianas. It is a long, woody perennial twiner; e.g., Bauhinia vahlii. 

(c) Tendril climbers. It is a weak stemclimbing by its slender, leafless, spirally coiled structures, known as tendrils. Tendril is sensitive to touch and can be a modified axillary branch (e.g., Passiflora), branch tip (e.g., Vitis) or inflorescence or a floral bud (e.g., Antignon, Cardiospermum,) 

(d) Root climbers. Such climbers give out adventitious roots at each node which stick to the support e.g pothos scandens money plant piper betle (betle) 

Modifications of Stem 

In most of the plants the stem is aeri: upright and bears leaves, flowers and fruits. In some plants however, the stem gets modified to carry out specific functions such as perennation, vegetative propagation, synthesis and storage of food, etc. Various modifications of stem are as follows 

(1) Underground modifications of stem. 

(2) Sub-aerial modifications of stem and 

(3) Aerial modifications of stem. 

Underground modifications of stem 

Stems of some plants get permanently lodged in the stem  

can be easily distinguished from roots on the basis soil for the purpose of perennation, vegetative propagation and storage of food. Underground stems of following characteristics. 

(1) presence of nodes and internodes, Scaly of small leaves 

(2) presence and adventitious roots at the nodes, 

(3) presence of buds in the axil of scale leaves lie dormant during unfavourable which conditions, and 

(4) internal structure. Some important types of underground stems are described below. 

1. Rhizome. It is a thick, prostrate and branched stem growing horizontally beneath the soil surface. It has distinct nodes and internodes. The nodes bear small scale leaves with buds in their axil. These buds remain dormant and during favourable conditions develop into aerial shoots. The lower surface of the nodes gives out small slender adventitious roots, e.g., Zingiber officinale (ginger), Curcuma domestica (turmeric), swollen tip of the 


2. Tuber. It is the underground branch. This branch arises from the axil of a leaf on the main stem. The growth of 

3. Corm. Corm is a condensed form of rhizome growing vertically (not horizontally like rhizome) down into the soil. It is spherical to oval in shape and branched. Internodes are usually reduced and one or more axillary buds are present at the nodes in the axil of the scale 

leaves. Some of these buds grow into daughter corms. Corms bear adventitious roots either at the base or throughout the surface; e.g., Crocus sativus (saffron), Gladiolus, etc. 

4. Bulb. It isa highly condensed stem, represented by a short convex or slightly conical disc. On its upper surface are present large number of fleshy scale leaves surrounding a terminal bud at the centre of the disc. Few scale leaves bear buds in their axil. The fleshy leaves of the bulb store food in the form of carbohydrates. A few outer leaves which become dry and scaly, are protective in function. Large number of adventitious roots arise from the lower surface of the condensed stem. The common 

examples are Allium cepa, (onion), Polianthes (tuberose), Allium sativum (garlic), etc 

[II] Sub-aerial modifications of stem  

In some plants like mentha, doobgrass, water hyacinth, etc., the stem is weak and prostrate. It either creeps on the surface of the soil or is buried superficially. Aerial branches and adventitious roots are given off at the nodes which behave as independent plants when detached. Thus, sub-aerial modifications help in vegetative propagation. 

Sub-aerial modification of the stem are of the following four types 

1. Runner or sobole. It is a slender, prostrate aerial stem creeping horizontally on the surface of the soil. It has long internodes. At the nodes, axillary buds form new aerial shoots and roots are given off on the lower surface. Thus several daughter plants are linked by runners, each one of them capable of growing into individual plant if runners break off; e.g., Cynodon (doob grass), Oxalis sp. (wood sorrel), etc. 

2. Sucker. This is a sub-aerial branch arising from the basal underground portion of the main stem. Initially it grows horizontally below the surface of the earth but soon grows obliquely upward forming a leafy shoot. Suckers are much shorter and stouter than runners, e.g.Chrysanthemum,(mentha,Mentha arvensis,podina), etc. 

3. Stolon. It… 

Functions of Stem 

Functions of stem can be studied under following two headings: 

(1) Normal functions; e.g., mechanical support and conduction. 

(2) Special functions; e.g., food storage, water storage, perennation, vegetative propagation and photosynthesis. 

The above functions are described below briefly under separate headings. 

1. Mechanical support. Stem is usually erect, aerial, thick and stout which keeps the plant in upright position. It bears brancies, leaves, flowers and fruits. 

2. Conduction. Stem translocates water and minerals absorbed by roots to all parts of the plant. Similarly, the organic food synthesized by leaves is supplied to non-green cells of the stem and roots through stem. Cells of stem are structurally suited for upward and downward transport of water and food material are 

3. Food storage. Few underground (e.g., rhizome, bulb, tuber, corm) and aerial (e.g, sugarcane) stems serve as storage organs. 

4. Water storage. Many plants of dry habitats (e.g., cacti) have a mucilaginous substance foliage which stores enough water to support the plant in extreme dry conditions. typical 

5. Perennation. Underground stems like rhizome and corm, besides food storage, also serve as perennating organs. These stems lie dormant during unfavorable period and when the conditions are favorable, the axillary buds present in the axil of scale leaves, germinate and form new plants. 

6. Vegetative propagation. Underground and aerial modifications of stem help in vegetative propagation. 

7. Photosynthesis. In plants of arid habitats which shed their leaves, stem becomes flattened leaf-like (e.g phylloclade and cladode) to perform photosynthesis. In plants with scaly leaves (eg.. Psilotum, Equisetum, Casuarina) the stems have photosynthetic tissue. 

Differences between Root and Stem. 


1. Develops from the radicle. 

2. Descending portion of the plant axis. 

3. Normally positively geotropic and negatively phototropiC. 

4. Roots are non-green (except for the exposed roots of certain plants). 

5. Root hairs are always unicellular. 

6. Not differentiated into nodes and internodes. 

7. Does not bear leaf, flower and fruit. 


1. Develops from the plumule. 

2. Ascending portion of the plant axis. 

3. Normally positively photoropic and negatively geotropic. 

4. Stem is always green when young but may later turn brown due to the formation of bark. 

5. Stem may have both unicellular and multicellular hairs. 

6. Differentiated into nodes and internodes. 

7. Bears leaves, flowers and fruits. 

Differences between Phylloclade and Cladode. 


1. It is a green flattened part of a branch 

2. It is made of only one or two internodes. 

3. This modified branch has only limited growth. 

4 True leaves are reduced to scales or modified into spines 


1. It is a green flattened stem or its branches. 

2. It has many nodes and intermodes. 

3. Phylloclades are branches of indefinite growth. 

4. True leaves are caducous, instead leaves modified into scales and spines are present. 

Differences between Rhizome and Sucker 


1. It is the underground main axis of the plant. 

2.  In the soil rhizome may groW horizontaliy, obliquely or upright. 

3. The apical bud of rhizome does not necessarily 

form aerial shoot. 


1. It is the sub-aerial branch arising from the basal underground portion of the main axis. 

2Sucker usually grows horizontally. 

3. The apical bud grows into aerial shoot. 

Differences between Runner and Sucker. 


1. It is an aerial prostrate stem that creeps horizontally on the surface of the soil. 

2. It has long internodes. Aerial branches arise from the axil of the scale 

3.  Runners are above ground hence green. 

4.leaves present at the nodes. 

5. Runners do not function as rennating organ. 


1. It is an underground modification of stem. 

2. It has relatively short and stout internodes. 

3. Suckers are underground hence non-green. 

4. The underground horizontal branch grows obliquely upward forming aerial shoot. 

5. Suckers, being underground, also function as perennating organ. 

Differences between Corm and Bulb. 


1. It is a thickened underground stem. 

2. It is swollen and enlarged as it stores food. 

3. Distinct nodes and internodes are present. 

4. Food is stored in the stem. 

5. It is surrounded by brownish corky scale leaves. 

6. Apical buds develop into aerial shoot. 


1. It is condensed underground shoot. 

2. It does not store food and is reduced to a flat or conical disc. 

3. As stem is highly reduced, hence nodes and internodes are not distinct. 

4. Food is stored in the fleshy leaves which surround the terminal bud. 

5. It is surrounded by thin brown scale leaves. 

6. Apical bud develops into a flowering shoot, called scape. 

Difference between Corm and Tuber  


1. It represents the main axis (stem) of the plant. 

2. Stem stores food, hence is thick, fleshy and swollen. 

3. Distinct nodes and internodes are present; nodes are represented by circular rings. 

4. It is placed vertically in the soil. 

5. Adventitious roots arise from the basal part of the corm. 

6. Corms of the successive years persist and lie above or around the older corm. 

Stem tuber 

1. It is the swollen tip of the specialised underground branch of the stem. 

2. Stem does not store food and is reduced. 

3. Distinct nodes are absent; eyes are present in a spiral fashion in the small depressions. 

4. Their orientation is not definite. 

5. Tubers do not bear roots.  

6. Old tuber is completely exhausted in the formation new plants and new tubers develop at the tips or the special underground branches of the stem. 

Differences between Rhizome and Corm. 


1. It grows horizontally in the soil. 

2 It is cylindrical or flat and comparatively less specialized. 

3. It is usually branched. 

4. Nodes and internodes are distinct. 

5. Bears roots all along its length. 

6. Branches develop from the terminal bud. 

7. Rhizome is perennial and survives for several years. 


1. It grows vertically. 

2. It is a highly condensed and specialized underground stem. 

3. Corm is usually unbranched. 

4. Internodes are reduced. 

5. Adventitious roots arise onıy from the basal part. 

6. Branches develop from the axillary buds. 

7. Corm is also perennial but survives for only 2-3 years. 

Differences between Rhizome and Corm. 


1. It grows horizontally in the soil. 

2. It is cylindrical or flat and comparatively less specialized. 

3. It is usually branched. 

4.Nodes and internodes are distinct. 

5. Bears roots all along its length. 

6.Branches develop from the terminal bud. 

7. Rhizome is perennial and survives for several years. 


1. It grows vertically. 

2. It is a highly condensed and specialized underground  

3. Corm is usually unbranched. 

4.  Internodes are reduced. 

5. Adventitious roots arise only from the basal part. 

6. Branches develop from the axillary buds. 

7.  Corm is also perennial but survives for only 2-3 years. 

Differences between Underground Stem and Root. 

Underground stem 

1. Nodes and internodes are absent. 

2. Leaves are absent 

3.No buds are present. 

4. Branches are present but their origin is endogenms 

5. Possess root hairs and root cap 

6. Flowers and fruits are absent. 

7.Only few specialized roots store food. 


1. It is differentiated into nodes and internodes. 

2. Scale leaves are present at the nodes. 

3. Axillary buds are present in the axil of scale leaves. 

4. Branches are present and they arise exogenously. 

5. Root hairs and root cap are not present. 

6. Does not possess flowers and fruits. 

7. Usually perform the function of food storage. 

Differences between Climber and Twiner. 


1. It is also a weak stem. 

2. It does not possess any clinging or supporting 

3. It is sensitive to contact. 

4. It climbs up by coiling its body around the support climbing organs (e.g., money plant, Piper betle). 


1. It is a weak stem. 

2. It has specialised clinging organs which help in attaching (fixing) the plant to the support organ. 

3. It is not sensitive to contact 

4. It climbs up by fixing itself to the support with the (e.g Cuscuta) 

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