A Stem is a long structural part of the plant that bears leaves and flowers. Have you ever wondered about the role of a stem in the plant? The stem is the part of a plant that gives support and help to transport materials to all parts of the plant. It also protects and promotes development and growth in a plant. Stems in some plants are aerial, subaerial and undergo several changes. The plumule of the germinating seed develops into stems. It produces leaves, fruits, and flowers, among other things. Nodes and internodes are the distinguishing characteristics of a stem. The stem’s primary role is to sustain other sections of the plant as well as to conduct food, water, and minerals. Many plants’ stems have been changed to serve a variety of purposes, including storage, protection, photosynthesis, support, propagation, and perennation. Adaptation and survival are aided by modifications.

It is important for students to know about Plants, as they are an essential part of existence on earth. In this article, let’s learn about the types of stem, characteristics, parts, diagrams, functions (Primary and Secondary), and their significance.

Stem Definition

The stem is the ascending part of the axis that bears the leaves, branches, fruits and flowers. It develops from the plumule and epicotyl of the embryo of a germinating seed. It also bears buds which can be terminal or axillary.

Functions of Stem

Stem performs various functions and can be known as primary and secondary functions.

Primary Functions of Stem

(i) Stem bears fruits, leaves, and seeds in position.
(ii) The flower is held in a suitable position for pollination and fertilization to take place.
(iii) Stem is basically the foundation of a plant that later develops into a tree.
(iv) Stem transports water and minerals absorbed by the roots to all parts of the plant like leaves, flowers, fruits, etc.
(v) Stem helps the plant to stand straight and perpendicular to the ground.

Secondary Functions of Stem

(i) Stems store food in them as reserve food material.
(ii) Some stems also help in photosynthesis and vegetative propagation.
(iii) Underground stems help in perennation.
(iv) Stems are the plant storerooms where prepared food is stored in the form of starch.
(v) Some stems help to replicate vegetative propagation which helps to grow flowers and fruits.

Diagram of a Stem

Types of Stem

In many plants, stems perform various functions such as; perennation, vegetative propagation, food storage or synthesis, etc. The stem is mainly classified into three types which are further divided into different groups based on their modifications. Three types of stems are:

1. Aerial stem
2. Subaerial stem 
3. Underground stem

Aerial Stem

A stem with a vertical or upright growth habit above the ground is called the aerial stem. The aerial stems have two forms, i.e. reduced stem and erect stem.

Reduced Stems	This type of stem is reduced to a small disc. The nodes and internodes are not distinguished, e.g., carrot, radish, turnip, etc. In some aquatic plants, the reduced discoid stem is green and flattened to float on the surface of the water. It does not bear Ieavcs, e.g. Lemna, Wolffia, Spirodela. In underground structures also a reduced, non-green seem is found. Example: Garlic, onion, and lily.
Erect Stems	These stems are strong enough to remain erect or upright without any external support. Example: Bamboo, Bougainvillea, etc.

Subaerial Stem

In this type of stem, a part of the stem remains under the ground and the remaining part becomes aerial. The dormant bud which is present on the stem becomes active and develops lateral branches of vegetative reproduction.

Underground Stem

As the name suggests, stems that grow below the soil are called underground stems. Most of these stems help in the storage of food, water or minerals, propagation, and perennation. Bulbs, tubers, rhizomes, and corms are some examples of these.

Modifications in Stem

The various forms of modifications can be seen in these three types of the stem to perform many important functions like climbing for support, storage of food, protection, and vegetative propagation. Below are some examples of these modifications in each type:

1. Modifications of Aerial Stem

Stem tendril	In plants with weak stems, the axillary or terminal bud gets modified into a thread-like leafless structure called a tendril that can coil around support. Tendrils can be Axillary (arise from axillary buds), e.g., Passiflora, Extra axillary (develop near the axillary bud), e.g., Luffa, Cucurbita (pumpkin), etc., or tendrils formed by modification of apical and floral buds. Examples: Vitis vinifera, Antigono, etc.
Stem thorns	The axillary bud gets modified into thorns which are pointed, hard structures without or without leaves, branches or flowers. Their formation is in the axil of a leaf or apex of the stem. Examples: Bougainvillea (with extra axillary) Asparagus (with leaf spines).
Prickles	These are modified stems and also act as climbing organs. They protect the plants from grazing animals and also help in climbing in some cases. Examples: Prickly poppy, Rosa indica (rose), etc.
Phylloclades	Phylloclades are green, flattened structures that function as leaves of the plant. In xerophytic plants, leaves are modified into scales or spines to reduce transpiration. The stems here become thick, flattened, green, succulent, photosynthetic that helping the plant to grow in dry and xerophytic conditions. They have fleshy internodes and leaves are modified into small scaly leaves or spines. Examples: Opuntia, Euphorbia, etc.
Cladodes	These are phylloclades with only one internode. Cladodes are photosynthetic and cylindrical but non-fleshy. The true leaves of plants are reduced to spines or scales. Examples: Asparagus, Ruscus, etc.
Bulbil	These are modified stems that are developed either from a vegetative bud or a flower bud. A new plant is formed when they undergo vegetative propagation. Examples: Dioscorea bulbifera, Agave, etc.

2. Modifications of Subaerial Stem

These are grouped into the categories mentioned below:

Runner	These are creepers that run horizontally on the surface of the soil. Runners arise from axillary buds, nodes with scale leaves, and adventitious roots. They show vegetative propagation.  Examples: lawn grass (Cynodon dactylon), wood sorrel (Oxalis), etc.
Suckers	These are slender, horizontal branches with long internodes, creeping on the ground and rooting at the nodes. It arises as an axillary bud and grows for some distance away from the parent plant, it then produces even if detached roots and grows into a new plant. Examples: Wood-sorrel (Oxalis).
Stolons	Stolons are long, lateral branches that arise from the base of the stem. These grow aerially for some time and then arch downwards to touch the ground which gives rise to daughter plants. Examples: Jasmine (Jasminum), peppermint (Mentha piperita).
Offsets	These are lateral branches that bear short internodes, in aquatic plants they are found to be shorter and thicker. Rosette of leaves upwards (aerial) and clusters of roots downwards are bared by nodes. Examples: Water lettuce (Pistia), water hyacinth (Eichhornia crassipes), etc.

3. Modifications in Underground Stem

The underground stem is divided into the following categories:

Rhizome	These are non-green prostrate thick stems growing horizontally beneath the soil surface with distinct nodes and internodes. The nodes bear small scaly leaves with buds in their axils, they also bear apical buds. Example: ginger (Zingiber officinale), banana (Musa paradisiaca), etc.
Bulb	In some plants, the internodal part becomes highly reduced due to which leaves become condensed (rosette) and take up the function of storage and become fleshy. Here, the stem reduces to a disc-shaped structure. The base of this disc produces numerous adventitious roots. Example: onion (Allium cepa), lily (Lilium bulbiferum), etc.
Tuber	Tubers are swollen terminal ends of underground stem branches that are used for vegetative propagation. These are covered with many depressions called eye or bud representing nodes. Example: Potato (Solanum tuberosum)
Corm	This is the highly condensed form of rhizome which is short, thick and grows in the vertical direction. The corm has nodes and adventitious roots at the base bear buds. The axillary buds are present on the sides. Example: Amorphophallus (elephant foot, vern, suran), Colocasia.

Characteristics of Stem

Following are some of the characteristics features of a stem:

1. The stem is the ascending part of the plant that grows in upward directions (except for a few), away from the soil (negatively geotropic), and towards the light (positively phototropic).
2. There are nodes and internodes in the stem, even if it is an underground stem. Node is the stiff region where leaves are born, and internodes are regions between two nodes.
3. The stem apex is always apical in position and bears terminal buds. These buds develop into flowers, leaf or shoots. Flower buds are modified leaves that arise from meristem tissue. 
4. The stem bears multicellular stem hairs called trichomes on its external surface for protection and reduces transpiration rate.

Related Topics to Stem

1. Root 2. Respiration in Plants 3. Essential Elements of Plants 4. Means of transportation in Plants

Summary

Now we have learned that the stem is the support system of the plant that bears, leaves, buds, flowers, and fruits that develops from the plumule and epicotyl of the embryo. It supplies water and nutrients absorbed by the roots to all the other parts of the plant.

Aerial stem, subaerial stem, and underground stem are the three main kinds of it. These stems show various modifications to help the plant in other important functions including food storage, photosynthesis, climbing, reproduction, etc.

FAQs

We have provided some frequently asked questions about Plant Stem here:

Q.1: Explain stem with diagram?
Ans: The stem is explained with the help of the diagram below:

1. The stem is the ascending part of the plant that grows in upward directions (except in some plants) that bears leaves, branches, fruits and flowers.
2. It has nodes and internodes, even if it is an underground stem. Node is the stiff region where leaves are born and internodes are regions between two nodes.
3. The stem apex is always apical in position and bears terminal buds. These buds develop into flowers, leaves or shoots. Flower buds are modified leaves that arise from meristem tissue. 
4. The stem bears multicellular stem hairs called trichomes on its external surface for protection and reduces transpiration rate.

Q.2: What are trichomes?
Ans: Stem bears multicellular stem hairs called trichomes on its external surface. These hairs help in protection from insects, germs, etc., and also to reduce the transpiration rate. 

Q.3: What are Phylloclades?
Ans: The stems of xerophytic plants become thick, flattened, green, succulent, photosynthetic that helps the plant to grow in dry and xerophytic conditions. These are called phylloclades. These structures function as the leaf of the plant. E.g., Opuntia, Euphorbia, etc.

Q.4: Name the opening on the stem through which transpiration occurs.
Ans: Cuticle, lenticels, and stomata are the three openings through which the process of transpiration takes place. Stomata are mostly found in leaves of the plant but in some cases, it is also present in the stem. 

Q.4: Define stem.
Ans: The stem is the ascending part of the axis that bears the leaves, branches, fruits, and flowers. It develops from plumule and epicotyl of the embryo of a germinal seed.

Q.6: What are the types of the stem?
Ans: There are 3 types of stems: Underground stem, Subaerial stem, Aerial stem. 

Q.7:  How do plant stems grow?
Ans: The stem of a plant usually grows in upward directions (except in some plants). It increases in length and width by continuous multiplication of cells in layers. Unlike leaves, the stem does not stop growing after a certain stage. It shows stimulus towards the light, it shows positive phototropism that means it grows towards the light.

Q.8: Briefly describe 3 functions of the plant stem?
Ans: 1. The primary functions of the stem are to provide support to various parts of the plant and transportation of water and minerals to leaves, flowers, buds, fruits, etc.
2. It promotes important processes such as photosynthesis, pollination, fertilization by holding leaves and plants in the right positions.
3. Other functions include synthesizing and storing food, vegetative propagation, transpiration, etc.

Q.9: Write about modifications seen in underground stems?
Ans: Underground stems show modifications like rhizome, bulb, tuber, and corm. 
1. A rhizome is a non-green that grows horizontally beneath the soil and bears nodes with small-scale leaves and buds.  E.g., ginger (Zingiber officinale).
2. The bulb is a stem reduced to a disc-shaped structure and produces numerous adventitious roots from its base. E.g., onion (Allium cepa).
3. Tubers are swollen terminal ends of underground stem branches that are used for vegetative propagation. These are covered with many depressions called eye or bud representing nodes. E.g., potato (Solanum tuberosum). 
4. The corm is the highly condensed form of rhizome which is short, thick, and grows in the vertical direction. The corm with nodes and adventitious roots at the base bears buds. The axillary buds are present on the sides. E.g., Amorphophallus. 

Now that you are provided with all the necessary information on Stem and we hope this detailed article on Stem is helpful. If you have any queries on Stem or about this article, ping us through the comment box below and we will get back to you as soon as possible.