TABLE OF CONTENT
S.NO CONTENT PAGE NO
Introduction 1
1.
2. What is Pollination 1-2
3. Parts of flowers 2-3
4. Kinds of Pollination 3-4
5. Agents of Pollination 5-12
6. Outbreeding devices 13-14
7. Artificial hybridization 14-16
8. Conclusion 17-18
9. Bibliography 18
1
Introduction
Much of the flower diversity that you have observed thus
far this semester is because of adaptations for pollination
by different mechanisms. In this lecture, we will discuss
the main types of pollination mechanisms. However,
please keep in mind that there are always exceptions;
plants and animals that visit flowers have minds of their
own!
The vast majority of flowering plant species are pollinated
by insects; in fact, it seems that flowering plants and many
major groups of insects co-evolved together. Animals
other than insects can also be important pollinators: bats,
birds (especially hummingbirds), and even a few
mammals.
WHAT IS POLLINATION
'Pollination' is the mechanism to achieve this objective.
Transfer of pollen grains (shed from the anther) to the
stigma of a pistil is termed pollination
Abiotic pollination refers to situations where pollination is
mediated without the involvement of other organisms.
Only 10% of flowering plants are pollinated without animal
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assistance. The most common form of abiotic pollination,
anemophily, is pollination by wind. This form of pollination
is early dominant in grasses, most conifers, and many
deciduous trees,
Biotic pollination :The process of pollination requires
pollinators: organisms that carry or move the pollen grains
from the anther to the receptive part of the carpel or pistil
(stigma). This is biotic pollination.
PARTS OF FLOWERS
There are four whorls of a flower which are as follows:-
#1: The Calyx
The calyx, which is the outermost whorl of a flower,
protects the inner whorls, especially when the flower is in
its bud state. The calyx is made up of sepals, which are
two small green structures at the flower's base that look
like tiny leaves.
#2: The Corolla
The second whorl of the flower is the corolla, which is
composed of the flower's petals. The petals serve two
purposes: to protect the reproductive organs of the
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flower and to attract pollinators. Because of this second
purpose, they are usually brightly colored and scented
so that animals and insects will come close to them and
move around the flower's pollen
#3: The Stamens
The third whorl of a flower is the stamen, the male
reproductive part. The stamen is made of a thin vertical
thread-like structure called a filament and circular or
oblong structure called an anther. The anther produces
pollen, which is the male contribution to the reproduction
process in plants. It consists of microsporangium which
may be monothecous or dithecous.
#4: The Carpels
At the center of the flower is the fourth whorl the
carpels, which contain the pistil of the flower. The pistil
is the plant's female reproductive organ, which is
composed of three parts: the ovary, the style, and the
stigma.
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KINDS OF POLLINATION
1. Self-Pollination
2. Cross pollination
✓ SELF POLLINATION
The pollination of a flower by pollen from the same flower
(autogamy) or from another flower on the same plant
(geitonogamy).
Ex: pea plant, groundnut, barley
Self-pollination is promoted by certain floral adaptation.
Accordingly self- pollination is of two types i.c., autogamy
& geitonogamy.
Autogamy:
In this type, pollination is achieved within the same
flower. Transfer of pollen grains from the anther to the
stigma of the same flower.In a normal flower which
opens and exposes the anthers and the stigma,
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complete autogamy is rather rare. Autogamy in such
flowers requires synchrony in pollen release and stigma
receptivity and also, the anthers and the stigma should
Autogamy occurs by two methods:
chasmogamous: The anthers and stigmas of open
flowers are brought together by growth, bending or folding.
Ex: peas, beans, hibiscus
Cleistogamy: In cleistogamous flowers, the anther
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.
Ex:oxalis,viola,
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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 flowers often show modifications
.
Xenogamy /allogamy
The transfer of pollen grains from the anther of one flower
to the stigma of a genetically different flower. It is also
called xenogamy (Gk, ) includes both geitonogamy and
xenogamy. Cross pollination is performed with the help of
an external agency.
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Agents of Pollination
BIOTIC AGENTS (animals)
It refers to the transfer of pollen grains through the agency
of insects like moths, butterflies, wasps, bees, beetles,
etc.
Ex: Salvia, Yucca, Ficus
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Characters: or brightly colored.
● Most insect pollinated flowers have a landing
platform.
● The pollen grains are spiny, heavy and surrounded by
a yellow oily sticky substance called pollen kit.
● Stigmas are often inserted and sticky.
● Some flowers provide safe place to insects for laying
eggs, e.g., Yucca.
➤It refers to the pollination brought about by birds
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➤Pollination by butterfly, example the Indian paintbrush
(Castilleja sp.) by swallowtail butterfly.
ABIOTIC AGENTS
1.wind pollinated
It is a mode of cross pollination or transfer of pollen grains
through the agency of wind.
Ex: Coconut palm, Date palm, Maize, many grasses,
Cannabis.
Characteristics:
● The flowers are colorless, odorless and nectarless.
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● Pollen grains are light, small and winged or dusty, dry,
smooth, non-sticky and non wettable.
● Stigma is hairy, feathery or branched to catch the
wind-borne pollen grains.
● Pollen grains are produced in very large number
II. Hydrophily ( water pollinated)
It is the mode of pollination or transfer of pollen grains
through the agency of water.
Ex: Zostera, Vallisneria
Characters:
● Flowers are small and inconspicuous.
● Nectar and odor are absent.
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● Pollen grains are light and non-wettable due to
presence of mucilage cover.
● Stigma is long, sticky but wettable.
It is further divided into two parts:➤ Pollination
occurring on the water surface.
Ex: Elodes, Hydrilla, Vallisneri
➤ pollination occurring beneath the
water..Ex:NajasCeratophylum,
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Outbreeding Devices
Self-pollination is common and more likely to happen in
the case of hermaphrodite flowers but a successive series
of self-pollination affects negatively and causes inbreeding
depression. This also results in homozygous genes. Thus
plants are adapted to promote cross-pollination. This is
known as outbreeding. Factors which encourage
cross-pollination are as follows:
Unisexual flower: If a flower is unisexual i.e., containing
only one sex either female or male, cross-pollination is the
only choice.
Non-Synchronization: Timing is important for successful
self-pollination. Pollen release and receptivity of stigma
should happen for successful self-pollination. Sometimes,
pollen matures and releases before the stigma is open
which leads to loss of pollen vitality or vice-versa. This
prevents self-pollination; even though the flower is
hermaphrodite.
Self-incompatibility (SI)
It is a general name for several genetic mechanisms in
angiosperms, which prevent self-fertilization and thus
encourage outcrossing and allogamy.
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ARTIFICIAL HYBRIDIZATION
Artificial hybridization : refers to instances in which
these crosses occur under controlled conditions, often
under the direction of plant or animal breeders.
PROCEDURE:
1. Emasculation:
The removal of the anthers of a flower in order to prevent
self-pollination or the undesirable pollination of
neighboring plants.
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2.Bagging
The emasculated flowers are immediately covered by
paper, plastic or polythene bags. The process is called
bagging. It prevents unwanted pollen to come in contact
with emasculated flowers. This prevents contamination
from foreign pollen grains.
3. Rebagging
When the flower is bagged flower attains receptivity, mature
pollen grains collected from anthers are dusted on the stigma
and the flower is rebagged.
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.
Pollination management is a branch of agriculture that
seeks to protect and enhance present pollinators and
often involves the culture and addition of pollinators in
monoculture situations, such as commercial fruit orchards.
The largest managed pollination event in the world is in
Californianalmond orchards, where nearly half (about one
million hives) of the US honey bees are trucked to the
almond orchards each spring. New York's apple crop
requires about 30,000 hives; Maine's blueberry crop uses
about 50,000 hives each year.
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Bees are also brought to commercial plantings of
cucumbers, squash, melons, strawberries, and many other
crops. Honey bees are not the only managed pollinators: a
few other species of bees are also raised as pollinators.
The alfalfa leafcutter bee is an important pollinator for
alfalfaseed in western United States and Canada.
Bumblebees are increasingly raised and used extensively
for greenhousetomatoes and other crops.
The ecological and financial importance of natural
pollination by insects to agriculturalcrops, improving their
quality and quantity, becomes more and more appreciated
and has given rise to new financial opportunities. The
vicinity of a forest or wild grasslands with native pollinators
near agricultural crops, such as apples, almonds or coffee
can improve their yield by about 20%. The benefits of
native pollinators may result in forest owners demanding
payment for their contribution in the improved crop results
– a simple example of the economic value of ecological
services. Farmers can also raise native crops in order to
promote native bee pollinator species as shown with L.
vierecki in Delaware and L. leucozonium in southwest
Virginia.
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BIBLIOGRAPHY
https://www.google.co.in/
https://www.wikipedia.org/
www.biology.lifeeasy.org
www.yourarticlelibrary.com
www.biologyreference.com
www.slideshare.net
Refrence books
Ncert book
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