POLLINATION - SELF POLLINATION & CROSS POLLINATION

          The transfer of pollen grain from the anther to the stigma of the same flower, or different flower on the same plant, or different flower of a different plant of the same species or allied species is defined as pollination.

            Types of Pollination:

            Pollination may be broadly divided into two types –

            1. SELF POLLINATION:- Self pollination is also known as autogamy. In this type, pollen grains of a flower fall on the stigma of a same flower or of the different flower of the same plant. It occurs not only in bisexual flowers but also in unisexual flowers of the same monoecious plant.

            Self pollination may be of three types –

            (a) Homogamy:- In this type, the anthers and the stigma of a bisexual flower mature at a time and some pollen grains may drop on the stigma of the same flower either automatically or through any agency. Example – Mustard.

            (b) Geitonogamy:- In this type, the transfer of pollen from anther of unisexual male flower or bisexual flower to the unisexual female or another bisexual flower occurring on the same plant. Example – Paddy, Wheat.

            (c) Cleistogamy:- In this type the bisexual flowers never opens. In such flowers self pollination is a must. Here the pollen grains are distributed on the stigma of the same flower. Such flowers are very small and insconspicuous. This type of pollination is common in the underground flower of Day flower, Ground nut, etc.

            2. CROSS POLLINATION:- Cross pollination is also known as allogamy. Cross pollination is the transfer of pollen grains from the anther of a flower to the stigma of another flower of two different plants of the same species or allied species by the help of outside agencies.

            Cross pollination is dependent on the external agencies which carry the pollen grains from the anther of one flower to the stigma of another flower belonging to the same species or closely allied species. Depending upon the nature of pollinating agency, cross pollination is of the following types –

            (a) Entomophily:- Pollination with the help of insects is termed as entomophily or insect pollination. Example – Sunflower, Orchids, Garden nustertium, etc.

            (b) Anemophily:- Pollination with the help of wind is called anemophily. This process of pollination is usually found in grass. Example – Rice, Wheat, Maize, etc.

            (c)Hydrophily:- Pollination by means of water is known as hydrophily. In many aquatic plants the pollination is brought about through the agency of water. Example – Vallisneria, Hydrilla, Elodea, Ceratophyllum, etc.

            (d) Zoophily:- When pollination is affected by animals including men, it is known as zoophily. This may be brought out by bats (Chiropterophily), birds (Ornitophily), snails (Malacophily), butterfly (Psichophily), honey bee (Hymenopterophily), man (Anthropophily), etc.

            ADVANTAGES AND DISADVANTAGES OF SELF POLLINATION

            ADVANTAGES

            1. It is a certain process.

            2. No wastage of pollen grains through external agencies takes place.

            3. Genetic uniformity in population is maintained and preservation of parental characters is possible for a considerable period of time.

            4. It is an economical process over cross pollination.

            5. Production of seed is ensured.

            6. This process is not dependent on any agency.

            DISADVANTAGES

            1. Viability of the seeds is less.

            2. It is not possible to get rid of any undesirable character.

            3. The future generation of the plant becomes weak and susceptible to diseases.

            4. Additional characters cannot be incorporated in such plants.

            ADVANTAGES AND DISADVANTAGES OF CROSS POLLINATION

            ADVANTAGES

            1. This process always gives rise to healthier offspring in subsequent generations.

            2. Offsprings are better adapted to struggle for existence.

            3. Production of seeds is many and they are more viable.

            4. Production of new varieties is possible by this method.

            5. The adaptability of the offsprings to their environment is better.

            6. Germination capacity of the seeds is better.

            7. Offsprings are less susceptible to diseases.

            DISADVANTAGES

            1. It is an uncertain process as this process is completely dependent on agencies.

            2. A considerable number of pollen grains are destroyed. Therefore, this process may be considered as uneconomical.

            3. Production of seeds is not fully ensured.

            4. Purity of genome cannot be maintained.

************