Pollination
The transfer of pollen grains from anther to stigma within same flower or different flower in
same plant or different plant of same species is known as pollination. It is of two types: 1. Self-
pollination 2. Cross-pollination
1. Self-pollination:
Transfer of pollen from anther of a flower to the stigma of the same flower (or flower of
same plant) is called self-pollination. Self-pollination can be of two types, autogamy and
geitonogamy,
(1) Autogamy:
The transfer of pollen grain from anther to stigma with same flower is known as autogamy.
This type of self-pollination occurs in bisexual flowers. Autogamy occurs by following three
methods:
(a) Homogamy:
This type of pollination occurs when the flowers are open. In this, anther and stigma mature
at the same time and pollination occurs within same flower. e.g. Catharanthus (Vinca),
Mirabills (four O’clock plant)
(b) Cleistogamy:
This type of pollination occurs when the flowers are closed and stigma only receives the
pollen from the anther within the same flower. e.g. Oxalis, Arachis hypogea, Commelina,
(c) Bud Pollination:
The sex organs develop before the opening of bud, thus internal pollination takes place. e.g.
Pea, Wheat, Rice, etc.
(2) Geitonogamy:
In this type of pollination, the pollen grains of one flower are transferred to the stigma of
another flower in same plant or genetically similar plant. This may occur in both unisexual or
bisexual flower.
Advantages of self-pollination
Helps to maintain the pure lines.
Can preserve parental characters.
It always ensures the production of seeds.
Disadvantages of self-pollination
Genetic defects or undesirable characters are transferred from parent to offspring.
It does not bring variation in offspring.
Immunity of the species decrease with continuous self- pollination.
Plant may go extinct with continuous self- pollination as adaptation to changing
environment is very less.
2. Cross-pollination:
Transfer of pollen grains from the anther of the flower of one plant to the stigma of the
flower of other plant by the help of agents is known as cross pollination. Agent may be
abiotic (non-living) or biotic (living). It is commonly seen in dioecious plants. It is highly
advantageous than self- pollination due to formation of new genotypes.
Types of cross- pollination
a. Anemophily: when the pollination occurs with the help of wind, it is known as
anemophily. In this when the air blows, along with the air pollen grains are also
blown and it reaches to the stigma of another flower. e.g., maize, poplar, oak, etc.
b. Hydrophily: Pollination through water current is called hydrophily. It occurs only in
aquatic plants. It may take place completely under water (hypohydrophily) or may
takes place on the water surface (epihydrophily). E.g., Zostera, Ceratophyllum,
Lemna etc.
c. Zoophily: pollination by animals.
Entomophily: Pollination that occurs
by insects is known as entomophily.
Insects are the chief pollinators.
Insects helping in pollination are
bees, flies, beetles and moths. Some
insects are diurnal (visiting flowers
which opens in day time) e.g. bees,
flies, beetles. While some are
nocturnal (e.g., moth). They visit
flowers which open after sunset.
Ornithophily: pollination by birds.
Chiropterophily: pollination by bat.
Malacophily: pollination by snail.
Conditions required for cross pollination
1. Uni-sexuality or Dicliny:
Plants bearing unisexual flowers are dioecious (e.g. Cannabis, papaya). Unisexuality is best
adaptive character for cross pollination.
2. Self-sterility or incompatibility:
Plants such as Passiflora, Potato, Malva, and Abutilon show self-incompatibility. In these
plants pollen grains from an individual flower cannot pollinate its own carpel as these pollen
grains fail to germinate on stigma of the same flower. Self- sterility in plants is under genetic
control which prevents the eggs in ovules being fertilized by pollens from the same plant.
3. Dichogamy:
It is a condition where in some hermaphrodite flower stamens and carpels of a flower do not
mature at the same time. It is of two types:
(i) Protandry:
Here anthers mature much earlier than the carpels of a flower, e.g., Sunflower,
Tagetes, Jasminum, Foeniculum etc.
(ii) Protogyny:
when carpels of flower mature much earlier than its anthers, e.g. Rose, Ficus
benghalensis, etc.
4. Heterostyly:
It is the phenomenon of disparity in the length of style and stigma that’s why effective self-
pollination is not possible, e.g., Primula, Lathynis, Oxalis etc.
5. Herkogamy:
Here, homogamous flowers develop some unusual structure to facilitate successful cross-
pollination. For instance, in caryophyllaceous flowers, the stigma grows much beyond the
limits of stamens so that its own pollen-grains fail to reach its own stigma. In Calotropis, the
corolla act as hood in between androecium and gynoecium.
Advantages of cross- pollination
Defective characters can be eliminated.
New and useful varieties can be produced.
Increases adaptability of species in changing environment.
Hybrid vigour can be observed.
Variation can be observed which leads to evolution.
Disadvantages of cross- pollination
Dependent on agent for pollination.
It is not a sure method.
Pure line genes cannot be maintained.
Plants consume large amount of energy to produce large number of pollen grains.
