Dispersal by Water
The male and female gametes in the flowering plants are produced in the pollen grains and embryo sac. The gametes produced by them are non-motile so they require agents for their movement. When they move, only then they will be brought together for fertilization. The process of pollination is responsible for this. By the process of pollination, the pollen grains are transferred to the stigma. Not just seeds, but there are fruits dispersed by water and also plants dispersed by water. We will study and learn about the characteristics of seeds dispersed by water. Abiotic and biotic factors are the two agents of pollination.
Types of Pollination
There are Three Types of Pollination, They are:
Autogamy: In this type of pollination, the anther is transferred to the stigma of the same flower. The plants have made many adaptations to ensure self-pollination. When both the whorls are present in the same flower, it is known as bisexuality. Homogamy is the time when both the anther and stigma matures at the same time. This ensures that both the male and female gamete mature at the same time. And the pollen grains and the stigma are matured in a synchronized manner. In cleistogamy, the flower does not open. This ensures that the anther gets fallen to the stigma. This is also very useful in the absence of any pollinating agents. Thus, it eliminates the pollinators from the process of fertilization.
Geitonogamy: In this, the pollens are transferred from the anther of one flower to the stigma of another flower but of the same plant species. Agents of pollination are required in this process. It can be termed as cross-pollination functionally and genetically it is similar to autogamy.
Xenogamy: In this, the pollen grains are transferred from anther of one flower to the stigma of another flower of different flower species. By this technique only, there are genetically different types of plants present.
Agents of Pollination
The agents of pollination are of two types. They are abiotic and biotic agents. Wind and water come under abiotic agents of pollination whereas biotic factors include animals. Anemophily is pollination with the help of wind and hydrophily is pollination by water.
Hydrophily
This is a technique of seed dispersal by water. Pollination or dispersal by water is seen in water lily seed dispersal. This pollination with the help of water is quite rare in flowering plants. It is limited to only thirty genera and they are mostly monocot plants. Examples are seed dispersal by water lotus, Hydrilla, marine water plant like Zostera. The characteristics of seeds dispersed by water are:
The pollen grains are light in nature and are generally unwettable.
The pollen grains are surrounded by a mucilaginous covering.
This covering protects them from being wet.
The stigma of such plants is long and sticky.
These characteristics of seeds dispersed by water give an advantage to the water plants to carry out the process of water pollination with ease.
Pollination by water
The Technique of Seed Dispersal by Water Can Occur at Two Places. They are:
Epihydrophily: This process of dispersal by water occurs on the surface of the water. It is seen in the Vallisneria plant. In this process, the female part of the plant has a very long pedicel. This pedicel helps the plant to reach the surface of the water. The male flowers are found floating on the surface of the water. These male flowers then release the pollen grains on the surface of the water. These pollen are carried away by water. This is known as passive transport as no energy is used and this pollen goes with the flow of the water and not against the flow of water. Out of these, some pollen reaches the surface of the water and thus the stigma of the flower and then the process of fertilization takes place.
Hypohydrophily: This process is seen in Zostera. It is also known as seagrass. It is a marine water plant. In this, the female flowers are submerged inside the water. The pollen grains have a ribbon-like structure. Here, these pollen grains are carried by water. They are carried passively with the flow of water currents and not against the concentration gradient. Due to this, some of the pollen then reaches the stigma and then they achieve pollination.
The flowers in the majority of the plants that are pollinated by water are present above the level of water. These water plants can be thus pollinated with the help of wind and insects.
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Important Characteristics of Flowers Pollinated by Abiotic Agents
The flowers that are pollinated by abiotic agents have developed special characteristics. These flowers are not very colourful. They also lack nectar. Flowers that are bright in colour, can easily attract insects and thus these insects can pollinate them. The nectar serves as a reward for them, for doing this pollination. The pollination that is carried out by abiotic agents is a kind of chance pollination. It is just a chance factor that the pollen grain may come in contact with the stigma of the flower. As it is a chance factor, these flowers produce pollen grains in very enormous quantities. The ovules are less as compared to the number of pollen grains. This gives the pollen grains a high chance of succeeding.
FAQs on Seed Dispersal by Water
1. What is seed dispersal by water?
Seed dispersal by water, also known as hydrochory, is a method used by some plants to spread their seeds using water currents. Plants growing in or near water bodies like rivers, lakes, or oceans often rely on this mechanism. The fruit or seed falls into the water and floats away, eventually reaching a new location where it can germinate and grow, thus preventing overcrowding and helping to colonise new habitats.
2. What are the key characteristics of seeds and fruits dispersed by water?
To be successfully dispersed by water, seeds and fruits typically have specific adaptations. The most important characteristics include:
- Buoyancy: They must be able to float for extended periods. This is often achieved through a lightweight structure, a spongy or fibrous outer coat that traps air, or air-filled chambers.
- Waterproof Covering: They possess a waxy or tough, impermeable outer layer to protect the embryo from water damage and decay during its journey.
- Durability: The seed must be resilient enough to survive long-distance travel and exposure to saltwater or mechanical damage from water currents.
3. Can you give five examples of plants that use water for seed dispersal?
Certainly. Many well-known plants rely on water for dispersal. Five common examples are:
- Coconut: The fibrous, air-filled husk makes it extremely buoyant, allowing it to travel across oceans.
- Lotus: The seeds are held in a spongy, buoyant receptacle that floats on water. Eventually, the receptacle disintegrates, releasing the seeds.
- Water Lily: The seeds are enclosed in an aril (a fleshy covering) that traps air, allowing them to float until the aril decays and the seed sinks.
- Mangroves: They exhibit vivipary, where the seed germinates while still attached to the parent plant, forming a propagule that drops into the water and floats vertically until it finds suitable mud to root in.
- Sea Kale: This coastal plant has buoyant, cork-like seed pods that can float on seawater.
4. How does a coconut, a classic example of dispersal by water, survive long sea voyages?
The coconut is perfectly adapted for long-distance sea travel. Its structure includes a fibrous and air-filled mesocarp (the husk), which provides excellent buoyancy, allowing it to float for months. The hard inner shell, or endocarp, creates a waterproof and durable casing that protects the seed (the coconut meat and water) from saltwater and physical damage, ensuring the embryo remains viable until it washes ashore on a suitable beach to germinate.
5. What is the difference between hydrochory and hydrophily?
This is a common point of confusion. Hydrochory refers to seed dispersal by water, which is a post-fertilisation process. Its goal is to move the offspring (the seed) to a new location to grow. In contrast, hydrophily refers to pollination by water, which is a pre-fertilisation process. Its goal is to move pollen from the male part of a flower to the female part to enable fertilisation.
6. How is seed dispersal by water different from seed dispersal by wind?
Both are abiotic methods but differ significantly. Dispersal by water (hydrochory) requires seeds to be buoyant and waterproof, and their travel is limited to the direction of water currents. Dispersal by wind (anemochory) requires seeds to be extremely lightweight, small, or have wing-like or parachute-like structures to catch the wind. While water travel is directional, wind can carry seeds in multiple directions over varied terrains, not just waterways.
7. Do all aquatic plants rely on water to disperse their seeds?
No, this is a common misconception. While many aquatic plants use hydrochory, a significant number do not. For instance, plants like the water lily have flowers that emerge above the water's surface. These flowers can be pollinated by insects, and their seeds may be dispersed by birds or other animals that eat the fruit. Therefore, living in water does not automatically mean a plant uses water for either pollination or seed dispersal.
8. What is the ecological importance of seed dispersal for aquatic and coastal plants?
Seed dispersal by water is crucial for the survival and expansion of aquatic and coastal plant populations. Its importance lies in:
- Colonising New Habitats: It allows plants to reach and establish themselves on new islands, riverbanks, or shorelines.
- Reducing Competition: By moving seeds away from the parent plant, it prevents overcrowding and reduces competition for resources like light, water, and nutrients.
- Maintaining Genetic Diversity: It facilitates gene flow between different populations along a waterway or coastline, enhancing the genetic health and adaptability of the species.
