Reproduction in Plants

IMPORTANT TERMS

 

Unisexual flower           A flower that contains either male or female gametes.

Bisexual flower             A flower that contains both male and female reproductive cells.

Gametes                     The male and female reproductive cells are together known as gametes.

Fertilisation                  The fusion of male and female gametes is known as fertilisation.

Zygote                        The cell which results after fusion of the gametes is called a zygote.

Embryo                       Embryo is a multi-cellular structure present within the seed which eventually matures into a plant.

Spores                         Spores are single-celled or several-celled reproductive bodies.

Stamen                        Male reproductive part of a flower.

Pistil                            Female reproductive part of a flower.

Seed Dispersal             Process by which seeds are scattered or carried away from the parent plant

Pollination                    Transfer of pollen grains from the anther to the stigma.

 

MODES OF REPRODUCTION

 

Reproduction is the process of producing young ones from their parents. A flower is the reproductive organ of a plant. There are several ways by which different plants reproduce. These are categorized into two types:

  1. Asexual Reproduction
  2. Sexual Reproduction

 

ASEXUAL REPRODUCTION

In asexual reproduction, the new plants are obtained without producing seeds. The formation of new plants takes place from the cells of a single parent, which can be a male parent or a female parent. The following are the common forms of asexual reproduction:

Budding

Budding is a type of asexual reproduction in which a small bulb-like cellular outgrowth, called bud, is formed from the cell. This bud keeps on increasing in size. Microorganisms such as yeast reproduce by budding. The yeast cell produces a bud which gets its own nucleus. The bud keeps on increasing in size and forms an independent organism which separates from the parent or mother cell. Budding is a characteristic of some unicellular organisms such as bacteria, protozoans and yeast.

In horticulture, the term budding refers to a method of plant propagation in which a bud of the plant to be propagated is grafted onto the stem of another plant.

Fragmentation

Fragmentation is a form of asexual reproduction. In this mode, plants such as algae break up into two or more fragments. Each fragment develops into a new plant.

Spore Formation

Spore formation is a form of asexual reproduction. Spores are single-celled or several-celled reproductive bodies. They are protected by a hard coat to withstand unfavourable conditions. When the conditions for germination are favourable, the spores germinate and develop into new plants. Some non-flowering plants such as ferns and mosses reproduce through spores. The spore-generating organs are frequently located on the undersides of leaves. The spores grow inside casings called sporangia.

Vegetative Propagation

Vegetative propagation is a type of asexual reproduction in which a new plant is developed from the vegetative parts such as stem, leaf and root. It can be done by both natural and artificial methods.

Natural Methods of Propagation

Through Roots

Some plants reproduce by their roots. E.g. The tuberous roots of sweet potato and Dahlia give rise to new plants. The food is stored in the roots.

Through Stems

Vegetative propagation can take place through modified underground stems. Rhizomes, tubers, corms and bulbs help in the multiplication of plants.

A Rhizome is a modified underground stem that have buds from which outgrowths are produced which give rise to new plants. E.g. Ginger

Tuber is a type of modified underground stem. They have buds or eyes which develop into new plants. E.g. Potato

Bulbs are very short underground stems with fleshy leaves that function as food storage. Bulbs often function in reproduction by splitting to form new bulbs or producing small new bulbs. E.g. Onion, Garlic

Corms are lot of rhizomes joined together which grow into new plants. E.g. Colocasia.

Through Leaves

Leaves of some plants develop small buds on their margin. These buds grow into new plant after falling on the ground. Bryophyllum is a plant which produces new plants from the bud in its leaves.

Artificial Methods of Propagation

Cutting

In this method, a young branch of a plant is cut off and placed in moist soil. After some time, this branch develops roots at the base and grows into a new plant. This method is mostly used in rose, sugarcane and Bougainvillea.

Layering

Layering is an artificial method in which a branch is lowered down and bent towards the ground and covered by moist soil forming a layer. After some time, roots arise from the covered part and grow downwards. The branch can be separated from the parent plant and allowed to grow into a new plant. Grapes, jasmine and bougainvillea are propagated by this method.

Grafting

Grafting is an artificial method used to develop new varieties of plants. In this method, the upper plant or the scion of one plant is placed over the roots of another plant called the stock. The scion and the stock are tied together. Gradually a new variety of plant develops. This method is commonly used in rose, mango, guava and other fruit plants.

SEXUAL REPRODUCTION

In sexual reproduction new plants are obtained from the seeds. It involves two parents and the fusion of male and female reproductive cells to form a single cell.

Male Organs

The male reproductive part of a flower is called stamen. It has two parts: Anther and filament. Anther contains pollen grains which produce male gametes.

Female Organs

Pistil is the female reproductive part of a flower. It has three parts: stigma, ovary and style. The ovary contains one or more ovules. The female gametes or egg is formed in an ovule.

POLLINATION

Pollination is the process by which pollen grains are transferred from the anther (Male organ) of a flower to the stigma (Female organ) of the same flower or another flower.

Pollen grains are produced by anthers.

TYPES OF POLLINATION

Pollination is of two types:

Self-pollination

If the pollen grains are transferred from the anther to the stigma of the SAME flower, it is called self-pollination.

Cross-pollination

If the pollen grains are transferred from the anther of one flower to the stigma of ANOTHER flower, it is called cross-pollination.

AGENTS OF POLLINATION

The following are the common agents of pollination:-

Wind

Pollen grains of some flowers are very light and get easily blown away by the wind from the anthers of one flower to the stigma of another flower e.g. rice, wheat and maize.

Water

Aquatic plants such as sea grass release their pollen grains into the water, which are carried to other flowers by water currents.

Insects

Insects feed on nectar produced by flowers. During feeding, some pollen stick to the body parts of the insects. When these insects feed at another flower, the pollen grains fall on the stigma where fertilization occurs.

FERTILISATION

The fusion of male and female gametes is known as fertilisation.

When male cells (pollens) are released into the ovule for the fertilisation with the female egg, the zygote is formed. After fertilization, the ovules change into seeds and the ovary enlarges and grows into a fruit. The other parts of the flower fall off.

GERMINATION

The process by which the embryo in the seed becomes active and grows into a new plant is called germination.

Seeds need right conditions to germinate which include adequate temperature, oxygen and water.

SEED DISPERSAL

The process by which seeds are scattered or carried away from the parent plant is known as seed dispersal. Seeds can be dispersed in a number of ways which include wind, water, animals etc.

Seeds which are light and have wing like structure or hair on them are dispersed by wind. E.g. Drumstick, Maple. Dandelion Seeds have radiating threads that form a parachute so that they can be carried to distant places by the wind.

Seeds are dispersed by the help of water. Seeds that have a spongy thick coat of fibre enables them to float and get carried away to far off places by water. E.g. Coconut, Lotus.

Seeds which have hooks or spines stick to our clothes or skin of animals and get scattered at different places. E.g. Xanthium

Some seeds are dispersed when the fruits burst with sudden jerk. The seeds pop out and get scattered. The fruits of pea, geranium, poppy and balsam burst open when they ripen.

Seed dispersal helps the plants to avoid overcrowding, prevent competition and enter new habitats.

INTERESTING FACTS

 

  • Some plants such as orchids do not need soil to grow. They get all of their nutrients from the air.
  • Flowers did not always exist; they first appeared 140 million years ago. Before that, ferns and cone bearing trees dominated the earth.
  • Sunflowers move throughout the day in response to the movement of the sun from east to west.
  • The white flower of the Amazon, water lily is the size of a football and turns purple after it has been pollinated.
  • The century plant or agave grows only one flower after many years and then it dies.
  • The seeds of proteas from South Africa germinate after they have been exposed to smoke.
  • Some seeds are poisonous to humans, such as the peach stone, which contains cyanide.
  • Dandelions are an excellent source of vitamins A and C, calcium, potassium and iron. Although looked upon as a weed, one cup provides almost 13,000 I.U. of vitamin A.
  • The Moon flower only blooms at night.