Reproduction is the process of producing the offspring of the same kind. Reproduction is mainly of two types namely, sexual and asexual.
Asexual mode of reproduction
It is the process which involves single parent in giving rise to offspring. It is the growth of a new plant from a part of the plant other than the seed.
Modes of asexual reproduction in plants
Plants reproducing by asexual mode do not produce gametes. A single parent multiplies to give rise to new individuals. Different modes of asexual reproduction in plants are elucidated.
- Vegetative propagation
- Spore formation
Vegetative propagation is the production of new plants from the vegetative parts of the plant. Roots, stems and leaves are called the vegetative parts of a plant. Vegetative propagation takes place by different methods like Leaf propagation, Root propagation, Underground stem propagation etc.
Advantages of vegetative propagation
- Vegetative propagation is an easier method than growing plants from seeds.
- Vegetative propagation is used in plants which do not produce seeds.
- Plants propagated through vegetative propagation require less time to grow.
- Plants propagated through vegetative propagation are more uniform to parents.
- Vegetative propagation helps in producing varieties in the plants.
a) Leaf propagation: Bryophyllum propagates vegetatively by the formation of leaf buds on the margins of a leaf. When the buds come in contact with moist soil, each bud is capable of growing into a new plant.
b) Root propagation: Sweet potato and Dahlia are cut into many pieces and are covered with mud. Each piece of the root tuber is capable of growing into young plant.
c) Stem propagation: In money plant, stem is cut and one side of it is buried in the soil. This stem from the parent plant grows into a new plant.
d) Underground stem tuber propagation: Potato is a stem tuber growing underground. It bears special structures called as eyes on it. When a potato is cut and buried under the soil. Each eye having a bud developed into a new plant.
e) Underground stem propagation: Ginger is an underground stem called as rhizome. It has lot of scaly leaves at nodes. These when buried under the soil gave rise to new plants.
Artificial methods of vegetative propagation
Many artificial methods are developed to propagate plants vegetatively. The process of propagating plants through artificial methods is called as artificial propagation. Different methods of artificial propagation are grafting, cutting, layering and tissue culture.
a) Grafting: It is the method which involves development of new varieties of fruit plants. Two twigs are selected form two different varieties of a plant in such a way that one twig should have a bud and the other twig should have a well developed root system.
- Scion is the twig which has a bud and stock is the twig with roots.
- Scion is placed on the stock and both are tied tightly so as to bind their tissues.
- Stock supplies the nutrients and scion enhances the growth of new variety of plant.
- We can combine two good characters from two different plants and develop them in a single new plant. e.g. Fruit plants.
c) Layering: This involves bending of a young stem towards the ground and burying it under the soil for development of roots . After a period of time, as the roots develop, the bent stem is cut off from the parent plant. This acts as a new plant. e.g. Jasmine.
d) Tissue culture: A mass of tissue is selected from the growing tip of the plant. This is termed as callus.
- Callus is placed on nutrient medium under controlled conditions.
- The root and stem production are initiated and their growth is enhanced by applying certain plant hormones in the medium.
- After the development of root and the shoot, the callus can be distributed in various petriplates.
- Each small piece of callus develops into a new plantlet.
- Plantlets are introduced into nursery ground for further growth. e.g. Asparagus
Budding involves the growth of a small bulb-like projection called as bud. This bud grows and detaches itself from the parent cell to grow independently into a new organism.
- Yeast reproduces by budding.
- Yeast is an unicellular organism belonging to the category of Fungi.
- It reproduces the new individual by the process of budding.
- Little amount of cytoplasm forms a protuberance.
- Nucleus divides into two. One nucleus migrates into the bud.
- Bud gets detached from the parent to develop into new individual.
- During budding, yeast respires and releases carbon dioxide.
- The carbon dioxide released helps the dough to puff up and become spongy. Hence, it is used to bake a cake and to make dough.
Fragmentation involves breaking down of filaments into fragments that grow into young ones.
- Algae are green, thread-like plants that grow in stagnant water, ponds and lakes.
- They float on the surface of the water causing algal bloom.
- Algae reproduce by the method of fragmentation.
- The body of the alga is called as thallus. it is not differentiated into stem, leaves and other structures of a plant body.
- As it is a multicellular organism, each cell strips of as a fragment and falls on the substratum
- It gets its strength to develop into new individual.
Spore formation is the method of developing new individuals by forming reproductive structures called spores.
- A spore is a small spherical or oval structure which protects the future individual in a thick protective covering.
- Spore germinates on a substratum under favourable conditions.
- Some organisms like ferns, some groups of fungi reproduce by spore formation.
a) Ferns reproduce by releasing spores that germinate into young ones.
b) Fungus reproduces by means of spores. Fungus like bread mould produce spores which germinate on moist organic surfaces. The cottony white mass on bread formed by fungus after spore germination is called a mould. Spores can survive in extreme conditions because of the protective hard coat.
c)Moss also reproduce by spores.
Regeneration cannot help plants in forming new individuals but can help them in regaining their lost parts. Grass develops with full vigour when cut i.e. it regains its lost parts.