There are a number of ways in which plants differ from animals but one of the most pronounced differences is that animals can move and plants cannot. Plants remain static at one place even though they grow vertically or horizontally depending on their growth pattern. But then how do these plants spread their seeds to grow at different places? It is interesting to note that nature helps them in this activity and this process is termed as dispersal of seeds.
Dispersal of seeds by Animal
Dispersion of seeds is carried out basically by four main agents namely air, water, birds and animals. Some plants also carry out their own dispersion.
When the plants themselves carry out the dispersal, the process is called dehiscence. In dehiscence or dispersion by explosion, a seed-containing structure such as a pod, bursts shooting the seeds into the air. These seeds land up at a distance depending upon the weight of the seed and the force with which they are thrown. Some of the plants that disperse their seeds in this manner include plants of the pea, mustard, and balsam family.
Air is also an effective dispersing agent for the seeds. Lightweight seeds fly form one place to another along with the wind. Some grass seeds have been detected at heights of more than a thousand meters. Lightweight orchid seeds are carried away by air to great distances form their parent plants. Seeds of some plants, such as dandelion and cattail, have puffy hair that helps them float through the air and land up elsewhere. The seeds of maple, ash and box elder have wing-like structures to move like small helicopters in the wind and thus get dispersed.
Dispersal of seeds by Wind
For dispersal by water, the seeds must be waterproof and able to float. Mangroves and coconuts have floating seeds with tough coats.
Birds and animals disperse seeds in a variety of ways. Some seeds have burrs or hooks, which get attached to the fur or the tails of the animals. They ca be carried to great distances traveled by the animals before falling off. Some seeds such as mistletoe are enclosed in sticky barriers. When a bird or animal eats these berries, the seeds get stuck to its feet, mouth or body. Some seeds are enclosed in juicy, tasty fruits, which are consumed by birds, animals, and human beings. These seeds remain unaffected by the digestive system and are passed out of the body, as in the faeces. The seeds of grapes, mulberry, pe3ars etc. are dispersed this way. Grazing animals such as cattle and sheep often disperse the clover and cereal crop seeds.
Dispersal of seeds by Water
Human beings often disperse seeds by throwing away apple cores, peach pits and other inedible seeds form juicy fruits. People carry seeds to great distances unknowingly when they carry them in fruits and other food items in long journeys.
Apart from these main agents of dispersion of seeds, there are other irregular agents that help in this process.