The study of immunology is essential within Biology Topics to understand the immune system.
Asexual Reproduction In Plants – Definition and Types
We will now discuss the asexual and sexual reproduction in plants in detail, one by one. Let us start with asexual reproduction.
In asexual reproduction, new plants are produced from existing plants without the production of seeds. The new plants obtained by asexual reproduction methods are exactly identical to the parent plants. The asexual reproduction in plants can take place by the following methods :
- Vegetative propagation,
- Fragmentation, and
- Spore formation.
We will now describe all these methods of asexual reproduction in plants in detail. Before we do that, we should know the meanings of the terms : node, axil and buds. These are described below.
Node. Node is a point on the stem (or branch) of a plant where a leaf is attached (see Figure). Buds are also present in the node regions of a plant.
Axil. Axil is the upper angle between a leaf stalk and the stem (or branch) from which it is growing (see Figure).
Bud. Bud is a compact, knob-like undeveloped shoot consisting of a shortened stem and immature overlapping leaves (or floral parts) (see Figure). Buds are the growing points of a plant. The buds at the end of a stem or branch are called terminal buds (see Figure).
The terminal buds lead to the elongation (lengthening) of stem and branches. Terminal buds may also develop into flowers. The buds present in the axil of a plant are called axillary buds (see Figure). Axillary buds are also called vegetative buds. When axillary buds (or vegetative buds) grow, they normally produce branches (with leaves). The axillary buds (or vegetative buds) can give rise to new plants. Thus, vegetative buds of a plant are used as a means of asexual reproduction for producing new plants.
Vegetative buds are normally present on the stems and branches of a plant (like that of a rose plant). Vegetative buds are also present on the modified, underground stems of plants (like potato plant). In some cases, vegetative buds can also develop on other parts of a plant such as roots and leaves. For example, vegetative buds are present on the modified, thickened roots of a sweet potato plant, and on the leaves of a Bryophyllum plant. The stems, roots and leaves are called vegetative parts of a plant (because they may contain vegetative buds). Please note that even the ‘vegetative buds’ are usually called just ‘buds’.
Vegetative propagation is an asexual method of reproduction in plants. In vegetative propagation, new plants are produced from the parts of old plants (like stems, roots or leaves). Vegetative propagation is also called vegetative reproduction. It is called vegetative propagation because the production of new plants takes place through the vegetative parts (stems, roots or leaves) of the existing plants. Vegetative propagation usually involves the growth and development of one (or more) buds on the old part of the plant to produce a new plant.
These buds are in the dormant state (inactive state) in the old part of the plant. When provided with suitable conditions (like food, moisture, warmth, etc.), these buds grow to form new plants. Some of the plants which are usually reproduced by the method of vegetative propagation are : rose, champa (Magnolia), potato, ginger, turmeric, sweet potato, Dahlia, mint, sugarcane, banana, Bryophyllum, strawberry, Gladiolus, cactus and grapes. We will now describe how new plants are produced from plant parts such as stems, roots and leaves of the existing plants.
(a) Vegetative Propagation by Stems
The stems (or branches) of plants normally bear buds in the ‘axils’ which can be used in vegetative propagation to produce new plants. New plants can be obtained from the stem (or branch) of an existing plant by the method of ‘cuttings’. A small part of stem (or branch) of a plant which is removed by making a cut with a sharp knife, is called a cutting. While making a cutting, care should be taken to see that there are some buds on it. Please note that a stem cutting or a branch cutting means the same thing. We will now describe how new plants can be grown from cuttings.
A small part of stem (or branch) of an existing plant having at least one bud on it ‘is cut with a sharp knife. This gives us a stem cutting. The lower end of stem cutting is buried in the moist soil [see Figure (a)]. The upper part of cutting having bud on it is kept above the ground. The cutting planted in soil is watered everyday.
After a few days, the cutting develops roots. The bud grows and produces a shoot (branch with leaves) [see Figure (b)]. Ultimately, a new plant is produced from the stem cutting of existing plant [see Figure (c)].
Cuttings are a means of asexual reproduction in plants. The new plant formed from a cutting is exactly similar to the parent plant. The plants like rose, champa, grapes, sugarcane, bananas, Bougainvillea, Chrysanthemum, cactus and henna (mehndi) can be grown by cuttings method (by using stem cuttings or branch cuttings).
Rose plants are propagated (or reproduced) by means of cuttings from stems (or branches) as follows: A piece of branch with a node (where a leaf is attached) is cut from an existing rose plant with the help of a knife. This piece of branch is the rose ‘cutting’. It has a bud in the axil (near the node). The lower part of the cutting is buried in moist soil. The upper part of cutting having the node (or bud) is kept above the ground. Water the planted cutting everyday. After a few days, the end of cutting buried in the soil develops roots. The bud develops into a shoot (branch with leaves). In this way, the branch cutting of a rose plant grows to become a new rose plant.
Money plant can also be grown by the cuttings method of vegetative propagation. We can grow money plant even in a jar of water by taking a stem cutting (with a node) from an existing money plant. An advantage of the cuttings method is that by using this method we can produce many new plants from just one plant quickly, without waiting for flowers and seeds.
Most of the plants around us have normal stems which grow above the ground. Some of the plants, however, have modified stems which are short and thick, and grow below the ground (or underground). The underground stems have buds from which new plants can be grown. Actually, such underground stems are called stem tubers. A tuber is the thickened underground stem (or root) of a plant which is swollen with stored food. The tuber has a number of buds. Each bud of the tuber can grow into a new plant when the old tuber (or its cutting) is planted in the soil in the next growing season. Thus, tubers can be used as organs of vegetative propagation to produce new plants. There are two types of tubers Potato is a stem tuber.
Potato tuber is the thickened, underground stem of the potato plant. Potato tuber (or its cuttings) can be used for the vegetative propagation of potato plants. Each potato tuber can produce more than one new potato plant. This happens as follows : A potato tuber has many buds (called eyes) on its body which appear like scars. When a potato tuber is planted in the soil, then all the buds of potato tuber start growing to produce new potato plants (see Figure).
Thus, one old potato tuber can produce many new potato plants. It is not necessary to plant the whole potato tuber in the soil to produce new potato plants. We can even plant cut pieces of potato in the soil to obtain new potato plants but each such cut piece should have a bud (or eye) on it. Thus, a cut part of a potato with a bud can grow into a new potato plant. Each potato plant produces more than one tuber, and each tuber has more than one bud (which produce more than one new plant). Due to this, the vegetative propagation method of producing potato plants by using ‘potato tuber cuttings’ is much faster than the production of potato plants from seeds.
Ginger and turmeric are also modified, underground stems swollen with food (but they are not tubers). The underground stems of ginger and turmeric plants have buds on their body. So, ginger and turmeric can be grown just like potato plants.
(b) Vegetative Propagation by Roots
The roots of plants normally do not bear buds. There are, however, some plants which have modified, thickened roots which bear buds. For example, sweet potato plant has modified roots thickened with stored food which are called root tubers. The root tubers of sweet potato have buds (eyes) on them which can grow to produce new sweet potato plants (see Figure).
Thus, sweet potato plants are reproduced by the method of vegetative propagation through their root tubers. Another plant called Dahlia also has root tubers. The root tubers of Dahlia have buds in them which can grow to produce new Dahlia plants. Thus, Dahlia plants are reproduced by the method of vegetative propagation through their root tubers. From the above discussion we conclude that the roots of some plants like sweet potato and Dahlia can be used to produce new plants.
(c) Vegetative Propagation by Leaves
Some plants reproduce themselves from leaves. The leaves of some plants develop buds on them. Such leaves having buds can be used as structures of vegetative reproduction in plants. One example of a plant which can reproduce from its leaves is Bryophyllum (Bryophyllum is also called sprout leaf plant). The leaves of Bryophyllum plant develop some buds in its margins (or edges) [see Figure (a)].
When a mature leaf of the Bryophyllum plant falls on the ground, then each bud can, grow into a new plant. Sometimes, even before a leaf drops off from a Bryophyllum plant, we can see new plantlets already growing on it [see Figure (b)], Thus, the leaves of Bryophyllum plant can produce new plants. Another plant called Begonia also reproduces by vegetative propagation through its leaves. The Begonia plant has buds on its leaves which can grow into new plants when the leaves fall on the ground. From this discussion we conclude that the two plants, Bryophyllum and Begonia, can be reproduced from their leaves.
The plants such as cacti produce new plants when their parts get detached from the main body and fall on the ground (singular of cacti is cactus). Each detached part of a cactus plant which falls on the ground can grow into a new plant. For example, if a part of the stem of cactus plant breaks off from the main plant body and sticks in the ground, it develops roots and grows to become a new cactus plant.
Advantages of Vegetative Propagation of Plants
The reproduction of plants by the methods of vegetative propagation has the following advantages :
(i) The new plants produced by vegetative propagation take much less time to grow and bear flowers and fruits as compared to the plants grown from seeds.
(ii) The new plants produced by vegetative propagation are exactly like the parent plant (because they are produced from a single parent). So, all the desirable features of the parent plant will be replicated in the new plants. On the other hand, the plants produced from seeds (made by sexual reproduction) have features of both the parents (male and female).