An Introduction to Pollination: Explaining Self Pollination and Cross Pollination
Pollination can be defined as the transfer of pollen grains from the anther to the stigma, occurring within the same flower, between different flowers of the same plant, or between flowers of different plants of the same species. This process can occur through various means, including air, water, rain, and insects. Ultimately, pollination leads to fertilization in plants. It can happen within a single flower or between different flowers on the same plant or between distinct plants of the same species. Many academic disciplines, such as botany, horticulture, entomology, and ecology, have investigated pollination. In the 18th century, Christian Konrad Sprengel was the first to study the pollination process as a relationship between the flower and its pollen vector.
Mechanism and Importance of Pollination
Pollination is essential for the reproductive cycle of plants. It involves the transfer of pollen within flowers on the same plant or between flowers on different plants of the same species. Pollination is categorized into two types: self-pollination and cross-pollination. The key distinction between these two lies in the location where pollen grains are deposited. Self-pollination happens within the same flower or another flower of the same plant, whereas cross-pollination occurs between flowers of different plants within the same species.
Difference Between Self-Pollination and Cross-Pollination
Cross-Pollination:
Cross-pollination refers to the transfer of pollen grains from the anther of one flower to the stigma of a flower on a different plant of the same species. This type of pollination is also known as allogamy. Plants adapted for cross-pollination may have mechanisms that reduce the likelihood of self-fertilization, such as differing maturation times for stamens and pistils. Examples of cross-pollinating plants include apples, tulips, lavender, strawberries, and beans.
Self-Pollination:
Self-pollination occurs when pollen grains are transferred within the same flower or between different flowers of the same plant. This type of pollination often takes place when external pollinators are not available. Examples include eggplants, peppers, tomatoes, legumes, and okra.
Self-pollination is further divided into three types:
(a) Autogamy
(b) Gietonogamy
(c) Cliestogamy
In autogamy, pollination occurs within the same flower, where pollen grains are transferred from the anther to the stigma of that flower. In flowering plants, autogamy manifests as self-pollination; examples include green gram, black gram, soybean, chickpea, and pea.
In geitonogamy, pollination occurs between different flowers, where pollen grains move from the anther of one flower to the stigma of another flower on the same plant. Monoecious plants—those that produce both male and female flowers—are more prone to this type of pollination. Examples include maize.
Cleistogamy refers to self-pollination that takes place before the flower opens. The pollen is either released from the anther within the flower or forms a tube that connects the anther to the ovules through the style. Unlike asexual reproduction methods like apomixis, it is a type of sexual reproduction.
Methods of pollination
There are two main ways of pollination:
Biotic Pollination-Approximately 80% of angiosperms rely on biotic pollination. Pollen vectors—organisms that carry pollen grains from the anther of one flower to the receptive carpel or pistil (stigma) of another—are crucial for this type of pollination. Around 1,500 species of birds and mammals visit flowers and may facilitate pollen transfer, but insects constitute the majority of these pollinators. This group includes monkeys, lemurs, squirrels, rats, and possums, alongside birds and bats, which are the most frequent visitors.
Abiotic Pollination: Abiotic pollination involves the movement of pollen between flowers through non-living agents, such as wind and water, rather than through living organisms. This type of pollination allows plants to concentrate on producing pollen instead of attracting pollinators with flowers and nectar.
Difference Between Self Pollination and Cross Pollination:
|
S.No |
Self Pollination |
Cross Pollination |
| 1. | Transfer pollen grains from one to another flower or within the flower of same plant | Transfer of pollen grains from anther to the stigma of another flower of different plant of same species |
| 2. | Small number of pollen grain required for fertilization | Large number of pollen grain required for fertilisation |
| 3. | Types of fertilization include: – autogamy and geitonogamy | It include :- allogamy |
| 4. | Pollen is released directly onto the stigma of either the same flower or a different flower on the same plant. | Pollens are transferred through wind, insect, water, animal |
| 5. | Smaller flowers are there in compare to cross pollinating flower | Flowers possess large petals, emit fragrance, and feature elongated stamens and pistils. |
| 6. | Examples are: – tomatoes, potatoes, apricot, oats, rice | Examples are:- apples, grapes, plums, pears |
Summary
Pollination is crucial for the reproduction of plants. There are two forms of pollination: cross-pollination and self-pollination, which can take place in flowers from the same plant or in flowers from different plants of the same species. Self-pollination occurs within the same flower or another flower on the same plant, while cross-pollination happens in a flower of a different plant of the same species. The main distinction between these two types of pollination lies in the location where the pollen grains land.