Pollination : Pollination is defined as the process of transfer of pollens from the stamens to the stigma. The flower may be same or different.
Direct Pollination : It occurs in Gymnosperms where ovules are naked. The pollen grains fall directly on the ovule. This is called direct pollination.
Indirect pollination : It occurs in angiosperms where ovules are enclosed in the overy of the carpel. Pollen grains fall on the stigma of the carpel, and not on the ovule. This is called indirect pollination.
Cleistogamous Flowers : Certain plants produce bisexual flowers which never open. Such flowers are called cleistogamous flowers.
Cleistogamy : The pollination occurring in cleistogamous flowers is known as cleistogamy, e.g. Commelina, Subularia.
Aerial flowers : These are normal type of flowers exhibiting cross pollination.
Geophilous flowers : These are cleistogamous flowers showing cleistogamy.
Chasmogamy : Pollination occuring in opened flowers is called chasmogamy. It is observed in most of plants.
Self-Pollination (Autogamy) : The transference of pollen grains from the anther to the stigma of the same flower is known as self-pollination. It is possible only in bisexual flowers.
Cross-Pollination (Allogamy) : The transfer of pollen grains from the anther to the stigma of another flower of the same kind is called cross pollination.
Geitonogamy : The transference of pollen grains from the anther of one flower to the stigma of a different flower on the same plant is called as Geitonogamy, e.g. Cucurbita, Coconut.
Xenogamy : In xenogamy the pollen grains are transferred from a flower of one plant to the stigma of another flower of different plant.
Advantages of cross pollination
1. Cross pollination gives more productivity of seeds.
2. In cross pollination, the yield is more.
3. Cross pollination gives healthier and larger seeds.
4. In cross pollination plants have more genetic variations.
5. The resistance to diseases is more in these plants.
Contrivances for Cross-pollination
1. Dicliny or Unisexuality : Production of unisexual flowers is called dicliny.
2. Dichogamy : In this condition stamens and carpels of a bisexual flower mature at different times. The androecium matures earlier than gynoecium. It is called protandry. If the gynoecium matures earlier than the stamens it is called protogyny.
3. Herkogamy : Arrangement of male and female reproductive organs at different levels in a bisexual flower is called herkogamy.
4. Heterostyly : In this the style is of different length in the flowers of the same species.
Contrivances for Self-Pollination
1. Homogamy : The condition in a flower in which the male and female reproductive organs mature at the same time, thereby allowing self-pollination.
2. Dichogamy : In this condition stamens and carpels of a bisexual flower mature at different times.
3. Safety Mechanism : In this mechanism cross-pollination fails to occur.
4. Movement of floral parts : In this inflorescence move by wind. The pollen grains may fall on the same stigma and self-pollination takes place.
5. Cleistogamy : Self-pollination occurs in cleistogamous flowers. In these flowers pollen released from the anthers are shed within the unopened flowers.
Agents which do Cross-pollination
Pollen grains cannot reach stigmas on their own. So they take help of some external agents for pollination. These are,
1. Anemophilly : Wind is the agent for pollination. Wind or anemophilly is useful for the plants which grow in windy places. This is also useful for the flowers which produce pollen in abundance.
2. Zoophily : Zoophily is the cross-pollination carried out by animals.
3. Entomophily : The pollination by insects is called entomophily. For this pollination, size of the flowers should be large, colour should be attractive, and smell should be such which can attract insects. Flowers which produce more pollen also attract insects, e.g. Rafflesia, Rose etc.
4. Ornithophily : Pollination carried by birds is called ornithophily, e.g. Bignonia.
5. Melacophily : Pollination carried out by snails and slugs is called melacophily, e.g. Aroids.
6. Chiropteriphily : Pollination carried by bats is called chiropteriphily, e.g. Bauhinia.
7. Cantharophily : Pollination carried out by beetles.
8. Hydrophily : Pollination carried out by water is called hydrophily.
9. Epihydrogamy : Pollination taking place on the surface of water is known as epihydrogamy, e.g. Vallisneria.
10. Hypohydrogamy : Under ground water pollination is called hypohydrogamy, e.g. Zosteva.
Self-pollinating Crops : Wheat, Groundnut, Chilies, Brinjal and Tomato.
Rarely self-pollinating crops : Paddy, Linseed.
Commonly cross-pollinating Crops : Carrot, Beet-root, Mango etc.
Rarely Cross-pollinating Crops: Jowar, Bajara, Cotton etc.
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