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On a windy day, have you ever seen seeds spinning through the air like helicopters? Maybe you’ve picked up a dandelion seed and blown it away, scattering its tiny, fluffy seeds everywhere? Are you ever curious about how these new plants grow and how seeds are dispersed? Let us learn briefly here what seed dispersal is and how it happens in this article. Seeds need to spread in the wild before they can find the best environmental conditions to germinate.
What is a seed?
In the lifecycle of a plant, seeds represent the embryonic stage. A flowering plant’s mature or fertilized ovule, which contains an embryo or young plant, is called a seed. In general, seeds contain three parts: embryo, endosperm, and seed coat.
A tiny plant, the embryo has a root, a stem, and leaves. Starch, oil, and protein often make up the endosperm, the nutritive tissue of the seed. The seed coat protects seeds and helps them remain viable for a long time.
When we eat fleshy fruits, we often avoid seeds, but many dry food products contain seeds. Among them are peanuts, lentils, beans, and peas – the most popular edible legumes.
What is seed dispersal?
Let’s break down the term “Seed dispersal”. All of us know seeds are the reproductive structures found only in spermatophytes (including flowering and cone plants). The ovule is the structure in plants that develops into seeds after fertilization. In later stages of plant growth and fertilization, these seeds serve as dispersal units. The term dispersal refers to scattering and distributing.
Now, we can define seed dispersal as a mechanism of scattering seeds (dispersal units, diaspores, or achenes) into different locations. Seeds cannot decide where their offspring will land, so their destiny depends on dispersal effectiveness. A good example of adaptation is seed dispersal.
Importance
A seed that falls to the ground under a parent plant might not receive enough sunlight, water, and nutrients from the soil if it falls to the ground. So, Plants have developed methods to disperse (move) their seeds since they are unable to walk around.
Types of seed dispersal
The root system anchors plants, therefore they cannot move, but their seeds can travel to new sites due to biotic and abiotic factors. The abiotic mechanism of dispersal is azoochory, whereas the biotic mechanism is zoochory.
Seed Dispersal by Wind
Annemochory is another name for it. In this type, seeds may float along with the breeze or flutter away with the wind. Dandelion seeds and maple seeds are dispersed by wind or air to distant locations. Airborne seeds have the following characteristics:
- Seeds are light in weight.
- Their size is also smaller
- Seeds of plants typically have wings, hairs or feathers, or both.
- A large number of seeds are produced by the parent plant.
- Wind carries seeds extremely far
Seed Dispersal by Water
Hydrochory is used by some aquatic and terrestrial plant species to disperse their seeds. When seeds float on water, they can travel a long distance. The seeds of aquatic plants that live in water bodies float downstream into the water where they germinate at new sites. Terrestrial plants, on the other hand, send their seeds deep into the soil during low tides of water and travel very far during high tides of water.
Seeds that are waterborne must possess the following characteristics:
- Presence of a strong and water-impermeable shell to protect the seed against water pressure.
- Presence of air pockets or buoyancy to help it float on the water until or unless the shell remains intact.
- Seeds must be produced by the parent plant near the water bodies so they can easily disperse by water.
Seed Dispersal by Gravity:
Gravity is the force of attraction that exists between all objects and matter in the universe. When the nuts fall to the ground by gravity, they travel a shorter distance downwards and after a few days are covered by the ground and germinate into new plants. Apples, dayflowers, canna, coconuts, gourds, and passion fruit are examples of plants whose seeds are distributed by gravity.
Seed Dispersal by Fire:
Since plants cannot escape a fire, certain plants have evolved a strategy to ensure that their seeds survive. Some types of pine trees need heat from a fire in order for their cones to open and release seeds. Other Australian plants, like banksias and eucalyptus, also rely on fire. It matters how intense and when the fire breaks out. The cones must be hot enough for them to open, but if fires occur too frequently, the plants won’t have the time to grow large enough to produce new seeds.
Seed Dispersal by animals and birds
Zoochory is the term for seed dispersal by animals. Fruits are consumed by both humans and animals, who discard the seeds. Few fruits and seeds have thorns or hooks, or they are edible. Man and animals consume fleshy, consumable fruits like mangos, oranges, papayas, and watermelons, and the seeds are tossed away, dispersing them.
Succulent Fruits: Animals are captivated by fruits because they are colorful, juicy, and nourishing. The seed travels through the animal’s feces after consumption, which may travel far from the parent plant.
Hooked Fruits: Fruits with curved hooks or spines, such as those of the cocklebur (Xanthium) and the tiger-nail (martynia), are carried to far-off locations by animals or people by attaching to their fur and cloths.
Many times, seeds are ingested by birds and then pass via their undigested droppings to distant locations. Birds help spread seeds in a similar manner.
Autochorous Dispersal:
As the name suggests autochorous dispersal is the type of dispersal in which plants disperse their seed by themselves without the assistance of any dispersal agent. Some plants, such as peas and milkweed, have seed pods that crumble when dried. The seed pod bursts open and expels the seed from the mother plant through a mechanism called the ‘bullochory’. Explosive dehiscence of the fruit is caused by changes in turgor pressure and internal tension. Examples of plant species undergoing bullochory are geranium species, euphorbia species, witch hazel, etc.
Benefits of Seed Dispersion
- Because there is less rivalry among members of the same species when it comes to seed dispersal, the many different seeds survival chances are high.
- When the right circumstances are present, the seeds can germinate.
- The ability to avoid being eaten is the primary benefit of seed distribution or seed dispersal.
- Different species can be found in a single location.
Summary
One of the most crucial processes in the regeneration of a plant culture or a group of humans is seed distribution. It indicates the potential recruitment area and serves as a development plan for the plant’s later phases. By transferring or transporting seeds away from their parent plant, seed dispersal is an adaptation process present in all seed-bearing plants that help to ensure the germination and survival of specific seeds in adult plants. The seed can be transported from one place to another using a variety of vectors.
Around us, there are numerous fruits and their seeds. Each seed is unique in terms of texture, shape, size, etc. The transfer of seed through various means from one location to another or away from the mother plant is seed dispersal.
The spread of seeds is crucial because it reduces competition among plants of the same species in an area for nutrients, sunshine, water, and minerals. It also enables them to develop in various environments. Small and light seeds can be easily carried over long distances by the wind. Water is primarily responsible for dispersing the seeds of plants that grow in or close to running water. Many seeds are distributed by adhering to animal fur. The primary benefit of seed dispersal is the ability to avoid seed and seedling mortality that is reliant on density or distance.
