Have you ever thought about the plants, trees we see everywhere? How do these reproduce? They can't even move or in other words, they are immobile. If not, today let's learn about the reproduction in plants. The process of reproduction in plants is called pollination. The plant that undergoes pollination is called a pollinated plant. There can be different types of pollination like self-pollination and cross-pollination and these two types also have subcategories, further, we will learn about them in detail. So let's get started with understanding pollination in flowering plants. We will study about types of pollination in plants.

Pollination is the process of reproduction in plants. This process can be of different kinds, like cross-pollination and self-pollination, and these two kinds also have subcategories which we will look at in detail. The word pollination comes from pollen grains.

Pollen grains are microscopic single-cell bodies that contain the male reproductive cell of the plants. Pollen are also called sperm cells or male gametes of the plant. Pollination occurs when pollen grains from the male part of the plant (anther) are transferred to the female part of the plant, referred to as stigma.

Before we move further we should know that flowers are the reproductive part of the plant.

After the pollen grains successfully land on the stigma a pollen tube is formed through the length of style, a long stalk that connects the stigma and the ovary of the flower. As the pollen tube formation gets completed the sperm cells from the pollen grain through the pollen tube are sent down to the ovary. As the sperm cell and egg cells meet, fertilisation takes place and fertilization of these cells result in formation of a seed. Later seed gets detached from the parent plant, seed grows into another plant and again in that plant occurs pollination. This way these immobile creatures reproduce through pollination.

Different Types of Pollination

There are basically two types of pollination: one is self-pollination and the other is cross-pollination.

While self-pollination is the primary type of pollination, cross-pollination is a bit complex. Now we are going to study self and cross-pollination in detail.

Self-Pollination

This type of pollination deals with only one flower and hence it is quite a basic type of pollination. When pollen grain from the male part of the flower (anther) falls directly on the stigma which is the female part of the same flower and fertilisation occurs, such type of pollination is called self-pollination. The plants that undergo self-pollination are referred to as self-pollinating plants. Some examples of self-pollinating plants are: wheat, apricot, rice, peanut etc.

Self-pollination though itself is a type of pollination, it further has sub-categories as well. Let's study them as types of self-pollination.

Types of Self-Pollination

Self-pollination can be of two types.

Autogamy
Geitonogamy

Autogamy

This type of self-pollination occurs where the transfer of sperm cells from the pollen grain to the stigma takes place within the same flower.

Autogamy is possible under some circumstances like

Both the anther and the stigma of the same flower should be open
Stigma should be prepared to receive the pollen when released from the anther
Anther and stigma should be close enough

Geitonogamy

This type of self-pollination occurs when transfer of pollen grains from the male part of the plant to the female part of the plant takes place in different flowers but of the same plant.

Geitonogamy seems more of a cross-pollination and requires a pollination agent but since it occurs in the same plant is called self-pollination.

Cross-Pollination

This type of pollination is more complex as here the transfer of pollen grain occurs from the anther of one flower to the stigma of a different flower. Cross-pollination is also called xenogamy. The movement of pollen grains in cross-pollination is possible through pollinating agents. Pollinating agents can be anything like animals, insects, winds and some other abiotic and biotic things. Generally, cross-pollination occurs in bright-colored flowers as their colour and odour attracts the insects like bees. Some of the cross-pollination plants are lavender, strawberry, apple, dandelion etc.

Types of Cross-Pollination

Pollination through biotic factors like animals, insects, birds etc.
Pollination through abiotic factors like wind, water etc.

Pollination through biotic factors involve the movement of pollen grains when they stick to some biotic agent like animals or bees or insects and as these agents move the stuck pollen grains get transported to another plant and fertilisation takes place.

Pollination through abiotic factors involve the movement of pollen grains when the wind blows or water is sprinkled or the rainwater spreads.

Let's have a look at wind pollination and through this, we will get to know about the pollination through other abiotic agents as well.

In wind pollination, pollination occurs through movement of pollen from the anther of one flower to stigma of other flowers by the wind. Plants that get pollinated by wind are called wind-pollinated plants. This was all about cross & self pollination.

Process

The term pollination originates from the pollen grains found in the flowers responsible for their reproduction.

These pollen grains are unicellular bodies that comprise a plant's male reproductive cell. These pollen grains are also known as sperm cells of a plant. This process takes place when the pollen of one plant is transferred to the female part of another plant, often known as the stigma.

Flowers are the parts of the plant that contain these reproductive organs.

When the pollen grains land on the stigma successfully, a pollen tube gets formed that is known as the style; this part is a long stalk that is responsible for making the stigma unite with the ovary (female part) of the flower.

After this process occurs, the sperm cells go to the ovary through style; when the sperm cells and the egg cells unite, fertilization occurs, resulting in the development of a seed.

This seed then gets detached from the parent plant and grows into another plant where it goes through the process of pollination again. The diagram below explains this process more visually:

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Types of Pollination

Pollination branches into two different types, Self-Pollination, and Cross-Pollination.

Self Pollination

This is the process where the pollination only occurs in one plant and one flower. When the pollen grains from the male parts of a flower transfer directly down to the stigma, the female part of another flower.

The plants that go through this process are known as self-pollinating plants. Some prominent examples of these plants are peanut, barley, wheat, rice, and apricots.

Self-pollination is of two types:

1. Autogamy: When the process of pollination takes place in the same flower itself. This happens only if:

The anther and the stigma of one common flower are open.
Stigma should have the ability to receive the pollen grains that are released from the anther.
Another and Stigma parts of a flower should be closer to each other.

2. Geitonogamy: This is the process of pollination that happens when the pollen grains of one flower fall into the female part of the other flower but both the flowers belong to the same plant.

This pollination is done with the help of a pollinating agent, hence it has characteristics that resemble cross-pollination, but since it happens within the same plant among two flowers, it is counted as a part of self-pollination.

Cross-Pollination

The process of cross-pollination is more complicated because the pollen grain from the anther of one flower gets transferred to another flower's stigma, but this happens between two flowers that belong to different plants. This type of pollination is also called Xenogamy.

This pollination is often challenging and requires the help of pollinating agents.

These pollination agents are organisms and natural phenomena like insects, animals, and wind. Commonly, this process takes place in bright flowers where their odor attracts the bees. Some well-known examples of cross-pollinating plants are Lavender, Apple, Dandelion, and Strawberry.

Cross-Pollination is also of two types based on the polluting agents that make this process happen:

Abiotic Cross-Pollination: Pollination occurring because of the movement of pollen grains from one flower to another due to agents like wind and rain.
Biotic Cross-Pollination: Pollination occurring because of the movement of pollen grains from one flower to another due to agents like animals, insects and birds.

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FAQs on Types of Pollination: Self vs Cross

1. What is pollination and what are its two main types?

Pollination is a crucial process in plant reproduction involving the transfer of pollen grains from the male part of a flower (anther) to the female part (stigma). This transfer is essential for fertilisation and the subsequent production of seeds and fruits. The two primary types of pollination are:

Self-Pollination: When pollen from the anther is transferred to the stigma of the same flower or another flower on the same plant.
Cross-Pollination (Xenogamy): When pollen from the anther of a flower on one plant is transferred to the stigma of a flower on a different plant of the same species.

2. What are the two different kinds of self-pollination?

Self-pollination is further divided into two types based on whether the transfer occurs within the same flower or between different flowers on the same plant:

Autogamy: This is the transfer of pollen grains from the anther to the stigma of the very same flower. For this to occur, the anther and stigma must mature at the same time and be positioned close to each other.
Geitonogamy: This involves the transfer of pollen from the anther of one flower to the stigma of another flower on the same plant. While it involves a pollinating agent, it is genetically identical to autogamy.

3. What are the different agents that help in cross-pollination?

Cross-pollination relies on external agents to move pollen between different plants. These agents are broadly classified into two categories:

Abiotic Agents (non-living): This includes pollination by wind (anemophily) and water (hydrophily). These methods are common in plants like grasses, maize, and many aquatic species.
Biotic Agents (living): This involves animals facilitating pollination. The most common biotic agents are insects (entomophily) like bees and butterflies, but also includes birds (ornithophily), bats (chiropterophily), and even snails.

4. Why is geitonogamy considered genetically a form of self-pollination but ecologically a form of cross-pollination?

This is a key distinction in pollination biology. Geitonogamy is considered:

Genetically self-pollination because the pollen and the ovule come from the same parent plant. This means there is no introduction of new genetic material, and the offspring have the same genetic makeup as the parent.
Ecologically (or functionally) cross-pollination because it requires an external pollinating agent (like an insect or wind) to transfer the pollen from one flower to another, a mechanism typical of cross-pollination.

5. How are wind-pollinated and insect-pollinated flowers different in their characteristics?

Flowers have evolved specific features to suit their pollinating agent. Wind-pollinated (anemophilous) flowers are typically small, not brightly coloured, and lack nectar or fragrance, as they don't need to attract animals. They produce large quantities of light, non-sticky pollen to be easily carried by the wind. In contrast, insect-pollinated (entomophilous) flowers are usually large, colourful, and fragrant, and they produce nectar to attract insects. Their pollen grains are often sticky or spiny to easily adhere to the insect's body.

6. Why is cross-pollination (xenogamy) considered more advantageous for a plant species than self-pollination?

Cross-pollination is generally more advantageous because it promotes genetic diversity. By combining genes from two different parent plants, it creates new combinations in the offspring. This genetic variation is crucial for a species' long-term survival as it:

Increases the chances of adapting to changing environmental conditions.
Reduces the risk of inbreeding depression, where continued self-pollination can lead to a reduction in fitness and vigour.
Promotes the evolution of new, more resilient traits.

7. What are some common examples of plants that undergo self-pollination and cross-pollination?

Different plants are adapted for different pollination strategies. Here are some common examples:

Self-Pollinating Plants: Many essential crops rely on self-pollination, including peas, tomatoes, wheat, barley, and rice.
Cross-Pollinating Plants: Most flowering plants, fruits, and vegetables require cross-pollination. Examples include apples, strawberries, pumpkins, lavender, and sunflowers.