Chapter 5: Pollination and fertilization

Pollination

The process of transference of pollen grains from the anther to the stigma.

Autogamy

Self-pollination, where pollen of same flower falls on its own stigma.

Geitonogamy

Pollination occurring between different flowers of the same plant.

Allogamy

Cross-pollination, where pollen from one plant fertilizes the stigma of another plant.

Self-pollination

The transfer of pollen from the anther to the stigma of the same flower or another flower of the same plant.

Cross-pollination

The transfer of pollen from the anthers of one flower to the stigma of another flower of a different plant of the same species.

Advantages of self-pollination

It is much surer, preserves parental characteristics, and no wastage of pollen.

Disadvantages of self-pollination

May lead to weakening of the variety, does not yield new varieties, defective characters cannot be eliminated

Advantages of cross-pollination

Produces healthier offspring, introduces genetic variation, and new varieties may be created.

Disadvantages of cross-pollination

Pollination is not guaranteed, a lot of wastage of pollen, and can be less economical.

Agents of pollination

Natural forces or organisms such as wind, insects, or water that facilitate the transfer of pollen.

Double fertilization

The process in flowering plants where one sperm fertilizes the egg cell and another sperm fuses with the polar nuclei to form endosperm.

Triple fusion

Occurs when one sperm nucleus and two polar nuclei unite during fertilization.

Hydrophilous

Refers to plants that are pollinated by water.

Entomophilous

Refers to plants that are pollinated by insects.

Anemophilous

Refers to plants that are pollinated by wind.

Artificial pollination

The human-assisted transfer of pollen from one flower to the stigma of another, often used in plant breeding. Includes bagging and emasculation.

Cleistogamous flowers

Flowers in which the reproductive structures remain hidden and lie close to each other.

Example of cleistogamous flowers

Pea, pansy

Homogamy

A condition where the anther and stigma of a flower mature at the same time.

Dichogamy

Condition where the anther and stigma mature at different times.

Protandry

A type of dichogamy where the anthers mature before the stigma.

Example - ladyfinger, sweat pea, Salvia, sunflower.

Protogyny

A type of dichogamy where the stigma matures before the anthers. Examples: Custard apple, peepal

Self-sterility

Condition in which even if the stigma receives pollen from the anthers of the same flower.

Ex - ray florets of sunflower, orchids

Herkogamy

Condition in which the pollen cannot reach the stigma, often due to barriers.
Ex - Pansy, Iris.

Heterostylyl

Condition in which the anthers and stigma grow at different heights.

Ex - Primrose, Oxalis

Characteristics of Entomophilous flowers

The flowers are large, brightly coloured, emit scent, and produce nectar to attract insects for pollination. They also have sticky pollen grains.

Characteristics of Anemophilous flowers

The flowers are small, not brightly coloured; the stamens are long and hang out and pollen is produced in large quantities.

Characteristics of Hydrophilous flowers

The pollen are in large numbers and have specific gravity almost equal to water and is caried by water.

Elephophily

Pollination by elephants.

Example of Elephophily

Rafflesia

Fertilization

The fusion of male and female gametes to give rise to the zygote.

Male inflorescence in Maize

Tassel

Cob

Female inflorescence in maize.