Pollination

Introduction
The flower is the part of the plant that brings about
reproduction by sexual means.
The androecium and gynoecium produce the male and
female gametes respectively, which on fusion, form the
zygote.
The fusion of the male and female gametes is termed
as fertilization. In order to bring about fertilization,
the most important step is to bring the two gametes
together. This is brought about by a process called
pollination.
There are two kinds of pollination : self-pollination and
cross-pollination.
Biswarup Majumder | Bio-World

Pollination
Pollination is the transference of pollen grains from the
anther of a flower to the stigma of a flower.
It may happen in three principal ways –
Autogamy (auto : self, gamy : marriage)
Geitonogamy (geitono : neighbouring, gamy : marriage)
Allogamy (allo : other, gamy : marriage)
The pollen of the same flower may fall on its stigma by
itself.
The pollen of another flower of the same plant may fall
on its stigma.
The pollen of a flower of another plant of the same
species may fall on its stigma.
Pollination must occur between plants of the same
species. Nature has so designed that only the pollen of
the same species of plant will survive and grow further
to continue the process for reproduction and the rest
of the types of pollen will fail to germinate and perish.

The word ‘pollen’, was used in science writing since 1760 and means “the fertilizing
part of flowers”. Earlier in history it meant “dust or fine flour”.
Self-Pollination
In self pollination, the pollen produced by the anther of
the flower is transferred to the stigma of the same
flower or to the stigma of another flower borne on the
same plant.
Adaptations for self-pollination :
Self-pollination can occur in bisexual flowers as well as
monoecious unisexual flowers.
Homogamy :
Cleistogamy :
Simultaneous maturation of anthers and stigma.
To ensure that self pollination takes place, the
anther and stigma of the bisexual flower or those of
the unisexual flowers must mature at the same time.
Examples : Mirabilis, Gardenia, etc.
This is a condition in which the flowers remain
closed.
There are some bisexual flowers that never open. As
a result, the pollen grain are distributed on the
stigma of the same flower.
Such flowers are small, inconspicuous and lack colour
and fragrance.
Examples : Commelina, wood-sorrel, etc.

Less varieties of offspring are produced as the offspring’s
genes are similar to those of the parent plant, therefore
the species is less adapted to changes in the environment.
Continued self-pollination may lead to offspring becoming
weaker, smaller and less resistant to diseases.
Advantages of Self-Pollination
Only one parent is required.
Offspring inherits its genes from parent plant. Hence
beneficial qualities are more likely to be passed down to
the offspring.
It does not depend on external factors e.g. insects or wind
for pollination.
Anthers are close to the stigmas of the same flower hence
there is a high possibility that self pollination will occur.
Less pollen and energy is wasted is self-pollination
compared to cross pollination.
Disadvantages of Self-Pollination
Self-Pollination

Cross-Pollination
Cross pollination is the transfer of pollen from the
anthers of flowers of one plant to the stigma of a
flower of another plant of the same species.
This transference can occur through wind, insects or
other agents.
Nature favours cross pollination. The vast majority of
flowering plants are cross-pollinated.
Incompatibility
In cross pollinated plants, the pollen
from a certain species often reaches the
stigma of a different species.
However, the chemicals present in the
stigma fail to stimulate the growth of the
pollen tube and hence no fertilization
occurs between plants of different
species.

Adaptations for Cross-Pollination
Unisexuality :
Dichogamy :
The flowers should be either male or female or borne
on separate plants, i.e., unisexual dioecious.
Examples : palm, papaya, etc.
In case of bisexual flowers, the male and female whorls
must mature at different times.
Protandry - the anthers of the flower mature
before the stigma, e.g. sunflower, sweat pea, etc.
Protogyny - the stigma of the flower mature before
the anthers, e.g. custard apple, peepal, etc.
Herkogamy :
Self-sterility :
The flowers possess structural features which do not
allow self pollination.
Example : in pansy, a hood covers the stigma.
The pollen from the anther fail to germinate on the
stigma of the flower.
Examples : ray florets of sunflower, orchids, etc.
Heterostyly :
Flowers have styles of different lengths and anthers
situated at different heights upon the corolla tube.
Examples : primrose, Oxalis, etc.

Two parent plants are required.
Depends on external factors e.g. insects or wind for
pollination.
Lower probability that cross pollination will occur
compared to self-pollination (because it involves transfer
of pollen grains from the anther of one plant to the stigma
of another plant).
More energy and pollen is wasted as compared to self-
pollination.
Advantages of Cross-Pollination
Offspring may have inherited beneficial qualities from
both parents.
Abundant and more viable seeds tend to be produced (i.e.
seeds are capable of surviving longer before germination) .
More varieties of offspring can be produced (greater
genetic variation).
Disadvantages of Cross-Pollination
Increases chance of survival of species to changes in
the environment.

Comparison

Agents of Cross-Pollination
Entomophilous (entomon : insect, phile : affinity)
Insect pollinated flowers (Example : Pea) usually have the
following characteristics –
Insect pollinators
Bees
Wasps
Flies
Butterflies
Some beetles

Anemophilous (anemo : wind, phile : affinity)
Wind pollinated flowers (Example : Maize) usually have the
following characteristics –

The honey bee dance language, used
to recruit nestmates to food
sources, is regarded by many as one
of the most intriguing communication
systems in animals.
Comparison

Hydrophilous (hydro : water, phile : affinity)
Flowers are found only in aquatic plants (Example :
Vallisneria). They have the following characteristics –
1. Flowers are small and inconspicuous.
2. Nectar and odour are absent.
3. Pollen grains are light and non-wettable due to the
presence of mucilage cover.
4. Stigma is long, sicky but wettable.
Types :
Epihydrophily Hypohydrophily
Epihydrophily – pollination occurs over the surface of
water.
Hypohydrophily - pollination occurs below the surface
of water.

Artificial Pollination
Procedure
When man himself
transfers pollen to the
stigma it is called
artificial pollination.
In the ancient
civilization of
Babylonia, it was a
common practice to
sprinkle “male flowers”
of palms on the
“female” flowers; of
course, at that time
they neither knew the
sexuality of palm
flowers nor anything
about pollination.

Pollination

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