Organization Of Plant

          Pollen grains are formed in the stamen which is the male part of the flower. These pollen grains are transferred to stigma of the carpel, the female part of the flower. This process of transfer of pollen grains is called pollination.

Fertilization

You might have seen that butterflies, honey bees and moths hover over flowers and fly from one flower to another. Why do they do so? Actually, they collect nectar (honey) from the flower. While they visit a flower, the pollen grains sticks to their bodies. When they sit on another flower, pollen grains fall on the stigma of that flower.

In this way pollination is carried out by insect. Birds and other animals also take part in pollination.

A pollen tube arises from the pollen grain. It passes through the style and reaches the ovary where male reproductive cell of the pollen grains fuses with the female reproductive cell of the ovule. This process is known as fertilization. As a result of fertilization, seed is formed form the ovule and the ovary ripen into a fruit.

Dispersal of seed and fruit

          When seed and fruit ripe, they drop from the plant. Plants need light, water and sir to live. If all seeds drop at the same place then only a few plants would be able to germinate and grow because all of them would not get sufficient light, water and air. That is why the seeds are dispersed far and wide so that maximum number of new plants may be produced. Air water and animals help in the dispersal of seeds.

Dispersal by air

            The seeds that are dispersed by air are light in weight and small in size. They are carried by wind over long distances. For example sumbal, cotton and aak seed have hair like fibres. Seeds of sheesham are flat and very light in weight.  Maple seeds have wings on both sides.

Dispersal by water

The seeds of plants that grow in or near water are carried far away by water. Lotus plants grow in pools and ponds. Their fruit fall in water when ripen and carried to a long distance by water currents. Lotus fruit is like a sponge and floats on the surface of water. Its seeds drop at the new places and grow into new plants. Coconut trees grow along the sea coast. Hair like fibres, present on coconut fruit, helps it to float on water. Its fruit floats long distances along tides. When it reaches some land mass, it grows into a new plant.

Dispersal by animals and men

          Men, monkeys, squirrels and birds eat juicy fruit. They take the fruit with them to distant places and throw away seeds after eating the fruit. New plants grow from these seeds. Some fruit have hard and small seeds. These seeds are eaten along with fruit, for example, guava. Such seeds are not digested. If animal goes far away, they are execrated along with feces. In this way, they are dispersed.

          Some fruit have rough surface or bristles on them. They stick to clothes, feathers of birds and hair of animals and are carried to distant places where they fall and so are dispersed.

Asexual reproduction in plants

In plants reproduction is of two types.

1.     Asexual reproduction

2.     Sexual reproduction

You know pollination and fertilization during which sexual reproduction leads to seed formation. New plants grow from the seeds. In asexual reproduction, new plants can develop from different parts of plant, e.g. stem, leaf. This method is comparatively simple and easy. Plants that develop as a result of asexual reproduction are exactly like their parents by using this method, large number of plants can be grown in a short time.

Cutting

This method is used in planting rose, potato, ginger, sugarcane, and bryophyllum plants. A 15cm to 20cm long portion of shoot of a rose plant is cut and buried in the soil. New shoots and leaves are produced form the buds present on nodes. Roots develop form the portion of the shoot that is underground.

You would have seen small pits on potatoes. These pits are called eyes. A bud is present in each eye. If potato is cut into small pieces in such a way that each piece has at least one bud and all are buried in soil, new plant will grow from each of the buds. Bryophyllum leaf is thick and fleshy. Its edges are wavy. A bud is present in each notch. If small pieces cut from a bryophyllum leaf are buried in the soil, new plants will grow form the buds.

Layering

          In this method the branch of a plant is buried in the soil so that its tip remains outside. Roots develop from the nodes on the portion of shoot which is underground and tip of the branch grows into a new plant. Jasmine and grass plants reproduce by this method.

Grafting

          This method is used to get fruit plants of good quality. The stem of a plant that has grown from seed is cut of a little above the ground. A branch of plant of good breed is also cut. This branch is tied firmly over the cut end of stem of the first plant. The grafted shoot grows into a new plant of the desired variety. Mango plants are raised by this method.