POLLINATION
Name : Sheryl Bhatnagar
Roll no : 2047
Sub : Reproductive biology
Course : Botany 2nd yr
POLLINATION
Definition:
The transfer of pollen grains
from the anther to the stigma of
a flower.
Pollen grains are immobile. They
cannot reach the stigma by
themselves. An external agent is
required for this. It can be wind,
water, animal, gravity or growth
contact.
POLLINATION
Two types of pollination
Self-pollination
Cross-pollination
SELF POLLINATION
It is the transfer of pollen grains from the anther of a
flower to the stigma of either the same or
genetically similar flower.
Accordingly, self pollination is of two types,
autogamy and geitonogamy.
AUTOGAMY
It is a type of self pollination in which an intersexual
or perfect flower is pollinated by its own pollen.
Autogamy occurs by 2 methods :
- Homogamy :The anthers and stigmas of
chasmogamous or open flowers are brought
together by growth, bending or folding.
- Cleistogamy : In cleistogamous flowers, the
anthers dehisce inside closed flowers. Growth of
style brings the pollen grains in contact with stigma.
Pollination and seed set are assured. Pollinators
are not required.
GEITONOGAMY
It is a type of pollination in which pollen grains of
one flower are transferred to the stigma of
another flower belonging to either the same
plant or genetically similar plant. In geitonogamy,
the flowers often show modifications similar to ones
found in xenogamy or cross pollination.
ADVANTAGES & DISADVANTAGES
Advantages of self Pollination: Disadvantages of Self Pollination:
1. It maintains the parental characters
or purity of the race indefinitely. 1. New useful characters are seldom
introduced.
2. Self pollination is used to maintain
pure lines for hybridisation
2. Vigour and vitality of the race
experiments.
decreases with prolonged self
3. The plant does not need to pollination.
produce large number of pollen
grains. 3. Immunity to diseases decreases.
4. Flowers do not develop devices for
attracting insect pollinators. 4. adaptability to changed environment
are reduced.
CROSS POLLINATION
(XENOGAMY, ALLOGAMY):
Cross pollination is the transfer of pollen grains
from the anther of one flower to the stigma of a
genetically different flower.
Cross pollination is performed with the help of an
external agency.
ANEMOPHILY
It is a mode of cross pollination or transfer
of pollen grains through the agency of
wind.
e.g., Coconut Palm, Date Palm, Maize,
many grasses, Cannabis.
Characterstics :
The flowers are colourless, odourless and
nectarless.
Pollen grains are light, small and winged or
dusty, dry smooth, nonsticky and
unwettable.
stigma is hairy, feathery or branched to
catch the wind-borne pollen grains.
Pollen grains are produced in very large
number.
HYDROPHILY
It is the mode of pollination or transfer
of pollen grains through the agency of
water.
Eg. Zoostera , vallisneria.
Characters:
Flowers are small and inconspicuous.
Nectar and odour are absent.
Pollen grains are light and unwettable
due to presence of mucliage cover.
Stigma is long, sticky but unwettable.
EPIHYDROPHILY HYPOHYDROPHILY
ENTOMOPHILY
the pollen grains are transferred to a
mature through the agency of insects like
moths, butterflies, wasps, bees, beetles,
etc.
Example:
Characters :
They are showy or brightly coloured.
Most insect pollinated flowers have a
landing platform.
The pollen grains are spiny, heavy and
surrounded by a yellow oily sticky
substance called pollenkit.
Stigmas are often inserted and sticky.
Some flowers provide safe place to insects
for laying eggs, e.g., Yucca.
ORNITHOPHILY
It is the mode of allogamy performed by
birds. Only a few types of birds are
specialised for this. They usually have
small size and long beaks.
Example :
Characters :
Ornithophilous flowers are usually brightly
coloured— red, orange, yellow or blue.
The floral parts are commonly leathery.
The ornithophilous flowers secrete
abundant watery nectar or have edible
parts.
Scent is often absent.
METHODS TO ENSURE CROSS POLLINATION
Dichogamy :
Anthers and stigmas mature at different
times in a bisexual flower so as to prevent
self pollination.
- Protandry Anthers mature earlier than
stigma of the same flower. Their pollen
grains become available to stigmas of the
older flowers, e.g., Sunflower, Salvia,
- Protogyny
Stigmas mature earlier so that they get
pollinated before the anthers of the same
flower develop pollen grains, e.g., Mirabilis
jalapa (Four O’Clock), Gloriosa, Plantago.
Herkogamy :
In some bisexual flowers the
structure of male & female sex
organs itself prove a barrier to self
pollination.
Self Sterility (Self
Incompatibility):
Pollen grains of a flower do not
germinate on the stigma of the
same flower due to presence of
similar self sterile gene (S,S3 in
pistil and S1 or S3 in pollen grain),
e.g., Tobacco, Potato, Crucifers.
Heterostyly :
There are 2 or 3 types of flowers with different heights of styles and
stamens.
(a) Diheterostyly (Dimorphic Heterostyly):
There are two types of flowers
- Pin eyed (long style and short stamens)
- Thrum eyed (short style and long stamens), e.g., Primula
(Primrose),
(b) Triheterostyly (Trimorphic Heterostyly or tristyly):
There are three types of flowers with different heights of styles.
e.g., Lythrum. Pollination occurs between anthers and stigmas of the
same height present in different flowers
ARTIFICIAL POLLINATION
This technique is used for the purpose of
Hybridization.
It involves pollination of desired female parents
with pollen from the desired male parent, taking
all precautions to prevent contamination of stigma
with undesired pollen.
In unisexual plants the procedure is simple but its
complicated in bisexual ones.
2 processes that takes place in bisexual flower :
- Emasculation
- Bagging
IMPORTANCE OF CROSS POLLINATION:
ADVANTAGES DISADVANTAGES
Cross pollination
introduces genetic re- •A factor of chance is always
combinations and hence involved in cross .pollination.
variations in the progeny.
Cross pollination •It is less economical.
increases the
adaptability of the •Some undesirable characters
offspring towards may creep in the race.
changes in the
environment.
•The very good characters of
It makes the organisms the race are likely to be
better fitted in the
spoiled.
struggle for existence.
The plants produced
through cross pollination
are more resistant to
diseases.
COEVOLUTION OF FLOWER AND ITS POLLINATOR
SPECIES:
Coevolution is the evolution in two species that interact
extensively with one another so that each acts as a major
force of natural selection on the other.
When one evolves a new feature or modifies itself, the
other evolves new adaptations in response of it.
This constant mutual feed back modification between the two
species is known as coevolution.
The coevolution of the flower and its pollinator species are
tightly linked with one another.
Disa nivea is a rare orchid found only in a few places in South
Africa, and until Johnson came to study it, no one knew how
it was pollinated. After a lot of patient orchid-watching, he and
his colleagues discovered that it is visited exclusively by the
fly shown in the picture. Its proboscis is well-matched to the
length of the orchid, and the orchid grows pollen in just the
right place so that they get stuck to the fly. You can see them
in this picture–the two dangling yellow packets on the fly’s
snout. This fly is named as Orchid fly.
