"Any fool can count the seeds in an apple. Only God can count all the apples in one seed."
― Robert H. Schuller
― Robert H. Schuller
Plants have limited mobility, thus for the propagation of their species they need to disperse their seeds to different places. Dispersal of seeds is basically a process in which seeds are transported to different places. This ensures that the plant develops in a variety of regions and increases the chances of survival and production. Dispersal of seeds is an important process.
There are different agents that help in dispersion of seeds. In this Gardenerdy article, we discuss why dispersion of seeds is necessary and how seeds are dispersed.
Why is Dispersal of Seeds Necessary?
Dispersal of seeds by various agents is very important for survival of the seed. Imagine if all the seeds of a plant fell in a small region below the tree. What will happen? The seeds will compete with each other and the parent plant for light, nutrients, and water. Thus, chances that not all seeds will grow in to healthy plants will be high.
Dispersal of seeds ensures that the seeds reach different habitats that are conducive for their growth. It also helps the plant to colonize new geographical areas.
Methods of Dispersal of Seeds
Heavy fruits usually fall from the tree. Sometimes, they even roll down some distance. After the fruit falls down, a secondary agent, like an animal or water, may even disperse it. Higher the fruit on the tree, more will be the distance it disperses to. Some fruits which do not have very hard covering may burst open after falling down leading to a better dispersion of seeds.
Plants in which seeds are dispersed due to gravity are coconuts, calabash, passion fruit, apples, hedychium, cerinthe, commelina, canna, etc.
Wind is one of the primary means of dispersal of seeds. It is also called anemochory. Seeds which disperse by winds are usually small, light, and feathery. Some even have hair that help the seed to float on wind. Some seed pods face upwards; as the wind pushes them, the seeds flow away. Since, the pod is bent at an angle the seeds don't fall down directly. There are some pods which face downwards as well. The seeds just fall down and are carried by the wind a fair distance.
Plants seeds that are dispersed due to wind are dandelions, swan plants, cottonwood tree, hornbeam, ash, cattail, puya, tecoma, willow herb, etc.
Imagine a pod bursting open and seeds spreading everywhere. Although it is not as dramatic as it sounds, many plants disperse their seeds by explosion. This phenomenon happens due to the Sun. The seed pod starts drying out due to heat. This creates tension along the walls of the pod. Thus, the pod splits open, and the seeds are violently ejected in the air.
Plants that disperse due to explosion are broom, euphorbia, geranium, okra, witch-hazel, etc.
Seeds can travel thousands of kilometers in water. Coconuts can float away in the sea and grow on an altogether different coast. Seeds of plants that grow in water are obviously dispersed by water. But, even plants growing along rivers, streams, and the sea are helped by water in dispersion of their seeds. Some seeds are light and hollow, thus they float on water, whereas coconuts have a hard wooden covering which helps them to float.
Coconuts, mangroves, foxglove, brooklime, yellow waterlily, water mint.
Animals play a major role in dispersion. They disperse seeds in two ways: epizoochory and endozoochory. Epizoochory is externally transporting the seeds. Some seeds cling to the fur of the animals and are carried to new areas. The seed may have projections or hair which help them adhere to the animal. Epizoochory is dispersal of seeds internally. Animals are attracted to fleshy fruits and consume them. Then, the seeds are defecated from their bodies. His helps the seeds reach different places. Birds are major proponents of this type of dispersal. Rodents, like squirrels, hoard their food. Sometimes, they forget where they have hidden the seeds. Thus, the tree grows.
Dispersal of seeds by animals is seen in sea holly, rambutan, date, sea grape, tamarind, raspberry, sunflower, etc.