Question 1 What is meant by dispersal of seeds?
Question 2 How do plants benefit from seed dispersal?
Question 3 Name three agents which help in the dispersal of seeds and fruits?
Question 4 What are the special features of seeds or fruits which are dispersed by wind?Name few plants whose seeds or fruits are dispersed by wind?
Question 5 What are the special features of seeds or fruits which are dispersed by water?Name few plants whose seeds or fruits are dispersed by water?
Question 6 What are the special features of seeds or fruits which are dispersed by animals?Name few plants whose seeds or fruits are dispersed by animals?
Question 7 What are the special features of seeds or fruits which are dispersed by explosive mechanism?Name few plants whose seeds or fruits are dispersed by explosive mechanism?
Dispersal Of Seeds and Fruits
Dispersal of seeds means to scatter seeds over a wide area. The seeds of some of the plants such (as seeds) but the seeds of other plants disperse in the form of fruits (because fruits contain seeds inside them).
The same kind of plants (and trees) grow at different places because their seeds are dispersed to different places by the various natural agents such as wind, water and animals, etc.
When the seeds become mature, then the whole fruit containing seeds or the individual seeds fall from the parent plant to the ground below. A plant produces many seeds. If all the seeds produced by a plant which fall directly underneath the plant germinate and grow there, then a large number of new plants would grow up close together in a small area of soil. The large number of new plants growing close together will compete with one another for water and minerals (from the soil), and sunlight, leading to shortage of water, minerals and sunlight. Due to insufficient water, minerals and sunlight, the newly growing plants will not be healthy and many plants would die.
In order to prevent overcrowding at the same place , the seeds and fruits of many plants have developed various ways which enable them to be carried a long distance away from the parent plant. When the seeds of a plant are dispersed, the new plants which grow from these seeds are far and wide and hence do not compete among themselves for water, minerals and sunlight.
Seed dispersal is beneficial to the plants because it provides the following advantages to the plants:
(i) Seed dispersal prevents the overcrowding of plants in an area.
(ii) Seed dispersal prevents the competition for water, minerals and sunlight among the same kind of plants.
(iii) Seed dispersal helps the plants to grow in new places (or new habitats) for wider distribution.
How seeds and fruits are dispersed
The main agents for the dispersal of seeds and fruits are wind, water and animals.Some seeds are also dispersed by an explosive mechanism in which the ripe fruits of some plants burst on their own by making a little explosion and throw their seeds away from the plant with a great force.The various seeds and fruits have some special features in them due to which they are adapted to be carried away easily by wind, water or animals.
(1) Dispersal of Seeds and Fruits by Wind
The seeds and fruits dispersed by wind either have wing-like structures or they have hair or they are very small and light, which helps them to be easily carried away by the blowing wind.
For example: (a) The seeds of drumstick plant have wings so that they can be carried away by wind to far away places and dispersed. Thus, drumstick plant has winged seeds. Similarly, the seeds of maple plant also have wings which help in their dispersal by the wind.
(b) The seeds of madar (aak) have hair which allow them to be carried away easily by the wind.The fruits of sunflower have hair which enable them to be blown away by wind and get dispersed. So, the sunflower plant has hairy fruits. The cotton plant has also hairy seeds which are easily carried away by wind and dispersed.
(c) The plants like grass, orchids and Begonia have very small and light seeds which can be easily blown away by the wind for dispersal.
(2) Dispersal of Seeds and Fruits by Water
The seeds and fruits which are dispersed by water develop floating ability in the form of spongy or fibrous outer coats.
The seeds of water lily plant and coconut plant are dispersed by water.
The seeds of water lily plant have a spongy outer coat which allows them to float in water and move to other places along with water currents. The coconut fruits have a fibrous outer coat which enables them to float in water and carried away by flowing water to far off places. It is due to the dispersal of coconut fruits by sea-water that coconut trees grow in all the coastal areas.
(3) Dispersal of Seeds and Fruits by Animals
Some fruits develop hooks on their surface by which they get attached to the hairy bodies of the passing animals and carried away to distant places.
These fruits may be carried several kilometres by the moving animals before they are rubbed off from their body and fall to the ground. When the fruits are dispersed by an animal, the seeds present in them are automatically dispersed.
When the fruits of Xanthium and Urena are dispersed by animals, the seeds of Xanthium and Urena present inside these fruits also get dispersed.
(4) Dispersal of Seeds by an Explosive Mechanism
When some fruits ripen, strain is set up in their walls until the fruits split into two halves (making a small explosion) and their seeds are thrown away from the plant with a great force in all directions. Thus, some seeds are dispersed when their fruits burst with a sudden jerk.
The ripe fruits of castor plant burst suddenly with a jerk and scatter the seeds far away from the parent plant. Similarly, the ripe fruits of balsam plant burst suddenly with a jerk and throw their seeds far away from the parent plant. Thus, the two plants whose seeds are dispersed by an explosive mechanism involving the sudden bursting of their ripe fruits are : Castor and Balsam