Dispersal of fruits and seeds
Most of the flowering plants produce enormous number of fruits and seeds. The fruits and seeds are dispersed to distant places. The fruits and seeds of many plants develop various devices for their wide dispersal. The dispersal of fruits and seeds may be caused by any of the following means:
Dispersal by wind:
Most of the plants have dispersal of their fruits and seeds by the agency of wind. Such fruits and seeds usually have various adaptations like wings, pappus, hairs etc.
Wings: The fruits and seeds of many plants develop one or more membranous wings with the help of which they are easily carried to distance places by the current of the wind. The fruits of plants like Shorea, Dioscorea etc., develop the wings either from the pericarp or persistent sepals. Similarly, the seeds of Moringa, Cinchona etc., also bear wings.
Hairs: The seeds of some plants bear hairs. These hairs help the seeds to be easily carried by the wind, example, Calotropis, Gossypium etc.
Parachute mechanism: Most of the plants of compositae family have persistent sepals modified into hair-like structure called pappus. When the fruits mature, the pappus open out like an umbrella and acts like a parachute. This helps the fruit to be carried by the wind to distant places as in sunflower, marigold etc.
Censer mechanism: Some types of fruits like legumes, capsules and siliquas dehisce in various ways. After ripening of these fruits, when they are shaken by wind current, they burst and the seeds are thrown out to longer distance. Such a mechanism of dehiscence of fruits and dispersal of seeds is called censer mechanism, example, Celosia, Datura etc.
Persistent styles: In some plants, the style remains till the maturity of fruits. Such fruits are small and light and the persistent style being feathery are easily carried away by the wind, example, Clematis.
Light and small seeds and fruits: Some fruits and seeds are so minute and light, that they are easily carried away by wind, example, orchids etc.
Dispersal by water:
Fruits and seeds of aquatic plants are usually carried by water current from one place to another. In case of the terrestrial plants, growing the near the seacoast and riverbank, dispersion takes place by the agency of water.
These fruits and seeds develop some special floating devices. They are usually light and the pericarp forms a spongy outer coat. Such a covering contains a large number of air spaces which keep them floating in water. The endocarp is usually hard and impervious to water. It protects the embryo from wetting and other injuries, example, coconut.
In lotus, the fruits are embedded inside the fleshy spongy thalamus which floats in water. After being detached, it is easily carried away by water current. The seeds of water lily are small and light and it is provided with spongy aril which encloses air. Therefore, these seeds float in water and are easily carried away by water current.
Dispersal by animal:
Many animals including human being help in dispersal of fruits and seeds of some plants. Such fruits and seed develop certain special devices by which they get attached to the body of animals or they attract the animals to carry them to distant places. Some of the devices for dispersal by animals are as follows:
Hook and spines: Some fruits and seeds are provided with spines or similar structures by which they cling to the fur of the animals and are carried to a long distance. Fruits of Tribulus, Achyranthes are provided with spines and those of Xanthium, Urena etc., bear curved hooks.
Sticky fruits and seeds: Fruits and seeds of some plants secrete mucilage or have sticky glands which stick to the body of the animals, example, Datura, Boerhaavia.
Fleshy fruits: Many fleshy fruits with attractive colours are often carried by birds and human beings to different places.
Edible fruits: Many edible fruits and seeds are carried by human beings to different places. Bird and other animals also carry such fruits from once place to another. Mice, squirrel, ants etc., are also responsible for such dispersal of seeds, example, mango, guava, orange rice etc.
Dispersal by explosive mechanism:
Some fruits at maturity burst with a jerk. As a result, the seeds are scattered and are dispersed to distant places. In case of Impatiens when the fruit ripes, it bursts suddenly and the valves roll up inwards, as a result, the seeds are ejected with a great force and are scattered on all sides.
Fruits of Phlox burst suddenly when the atmosphere is dry. Similarly, dry fruits of Ruellia also burst suddenly when they come in contact with water particularly after a shower of rain.
The seeds are also provided with curved hooks, called jaculators, which straighten out immediately and give jerks to the seed. Explosion of fruits of Bauhinia is also interesting to note. Long pods burst with a loud noise and the seeds are dispersed in all directions.