Pollination and Fertilization
The pollen grains contain 2 sperm nuclei.
Definitions
• Pollination is the process of transfer of pollen grains from the anther to the stigma
• The process by the pollen grain of one flower falls on the stigma of the same flower
on its own - Autogamy
• The process by which the pollen grains of one flower of a plant falls on the stigma of
another flower of the same plant - Geitonogamy
• The process by which the pollen grains of one flower fall on the stigma of another
flower on another plant - Allogamy
• The bisexual flowers which do not open even at maturity and their reproductive
structures remain hidden and close to each other, facilitating self-pollination, are
called as Cleistogamous flowers
• The large flowers with open petals and exposed reproductive structures are called
Chasmogamous Flowers. E.g. Oxalis, Hibiscus
• The condition in which the flower is either staminate or pistilate and facilitates only
cross pollination is called Unisexuality. E.g. Papaya, Palm
• The condition in which the female and male gametes of a bisexual flower mature at
different timings, thereby not facilitating self-pollination and facilitating cross
pollination is called Dichogamy.
• The condition in which the anther matures before the stigma is called Protandry. E.g.
Pea, Salvia, Sunflower
• The condition in which the stigma matures before the anther is called Protognvy. E.g.
Custard apple, peepal
• The condition in which the pollen grains fall on the stigma of the same flower but the
stigma fails to undergo further growth is called Self Sterility. E.g. Ray florets of
sunflower, orchids
• The condition in which the pollen of a flower cannot reach the stigma of the same
flower due to some mechanical or environmental disorder is called Herkogamy. E.g.
Pansy, Iris
• The condition in which the anther and stigma grow to different heights thereby not
facilitating self-pollination is called Heterostyly
Biological terms
• Insect Pollinated flowers: Entomophilous, Dahlia
• Wind Pollinated flowers: Anemophilous, Maize
• Water pollinated flowers: Hydrophilous, Vallisneria
• Bird pollinated flowers: Ornithophily, Bignonia, Canna
• Elephant pollinated flowers: Leptophilic, Rafflesia
• Removal of anthers from young plants: Emasculation
• Covering of flowers with plastic bags: Bagging
Only the pollen of the same species of plant will survive and continue to grow further for
the process of reproduction and the pollen of rest will fail to germinate and perish
Self-Pollination
Transfer of pollen from anther to stigma of same flower
Transfer of pollen from anther of one flower to stigma of another flower on the same plant.
Self-Pollination can occur only when:
The flower is a bisexual flower (having both pistil and stamen)
The plant has both staminate and pistilate flowers
The maturity time of both the stamen and pistil are at the same time
Cross pollination
Transfer of pollen from anther of a flower on 1 plant to the stigma of another flower on
another plant of the same species.
Fertilization
The union/fusion of the nuclei of male and female gametes is called Fertilisation
Pollen Grain
• double walled
• outer Exine
• inner Intine
• nucleus- tube nucleus and generative nucleus
Ovule
• Two protective coverings - Integuments
• Small opening in the integuments- Micropyle (Entry of pollen tube)
• Enclosed by integuments - Nucellus
• Inside the nucellus - Embryo Sac
The pollen grains is stimulated to germinate by the secretion of sugars by the stigma
Generative nucleus divided into two sperm nuclei called male gamete nuclei
The tube nucleus helps to provide direction for the growth of the pollen tube towards the
ovary
