Investigating the effects of environmental pollution is a significant aspect of Biology Topics.
What are the ways of plants disperse their seeds?
‘Dispersal of seeds’ means ‘to scatter seeds over a wide area’. Now, the seeds of some of the plants disperse as such (as seeds) but the seeds of other plants disperse in the form of fruits (because fruits contain seeds inside them). So, the dispersal of seeds also includes the dispersal of fruits.
In nature, the same kind of plants (and trees) grow at different places which are quite far away from one another. 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. We will now describe what will happen if all the seeds of a plant were to fall at the same place and grow there. We will also discuss the benefits which the plants get by seed dispersal.
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. This will harm the plants in the long run because their further spreading will be prevented.
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. In other words, the seeds and fruits of many plants are adapted for dispersal in wide areas. When the seeds of a plant are dispersed (or scattered), the new plants which grow from these seeds are far and wide and hence do not compete among themselves for water, minerals and sunlight. All the new plants get sufficient water, minerals and sunlight due to which they grow to become healthy plants.
Seed dispersal is beneficial to the plants because it provides the following advantages to the plants :
- Seed dispersal prevents the overcrowding of plants in an area.
- Seed dispersal prevents the competition for water, minerals and sunlight among the same kind of plants.
- Seed dispersal helps the plants to grow in new places (or new habitats) for wider distribution.
How Seeds and Fruits are Dispersed
Seeds and fruits of the plants are carried away (or dispersed) by wind, water and animals. So, 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. Please note that 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. We will now describe the dispersal of various types of seeds and fruits by wind, water, animals and explosive mechanism in somewhat detail.
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 [see Figure(a)]. Thus, drumstick plant has winged seeds. Similarly, the seeds of maple
plant also have wings which help in their dispersal by the wind [see Figure 20(b)]. Thus, maple plant has also winged seeds.
(b) The seeds of madar (aak) have hair which allow them to be carried away easily by the wind [see Figure (c)]. Thus, madar (aak) has hairy seeds. Similarly, the fruits of sunflower have hair which enable them to be blown away by wind and get dispersed [see Figure (d)]. 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 grasses, orchids and Begonia have very small and light seeds which can be easily blown away by the wind for dispersal.
From the above discussion we conclude that some of the plants whose seeds or fruits are dispersed by wind are : Drumstick, Maple, Madar (Aak), Sunflower, Cotton, Grasses, Orchids and Begonia.
2. Dispersal of Seeds and Fruits by Water. The seeds and fruits of some of the plants are dispersed 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 alongwith 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 (see Figure). Coconut fruits floating in sea-water are carried hundreds of kilometres away by the sea currents to other parts of land.
It is due to the dispersal of coconut fruits by sea-water that coconut trees grow in all the coastal areas (sea-shore areas). From this discussion we conclude that the two plants whose are : Water lily and Coconut.
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. The fruits of Xanthium and Urena plants are covered with numerous hooks due to which they are dispersed by animals (see Figure).
When the fruits of Xanthium and Urena are dispersed by animals, the seeds of Xanthium and Urena present inside these fruits also get dispersed. Thus, the two seeds/fruits dispersed by animals are: Xanthium and Urena.
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 two common examples of explosive fruits are castor and balsam. 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.