Pollination:Self and Cross Pollination

POLLINATION:
Pollination is transfer of pollen grains from anther to stigma of same or another flower of same or different plant with or without the help of external agencies is known as pollination.The self pollinated flowers are generally small,inconspicuous,colourless,odourless and nectarless.

TYPES OF POLLINATION:
1)SELF POLLINATION(AUTO GAMY):
The transfer of pollen grains from anther of a flower to the stigma of same or genetically similar flower is called self pollination.

CONDITION FAVOURING SELF POLLINATION:
1)HOMOGAMY:
This is the condition where the anther and stigma of bisexual flowers mature at the same period.
2)CLEISTOGAMY:
Some bisexual flowers never open but remains closed which finally favour the self pollination.
Eg:ground nut
ADVANTAGES OF SELF POLLINATION:
1)It preserve the parental character.
2)It does not need any external agency.Hence shows greater re abilities.
3)It is necessary for species which are at great distant from each other.
4)It is advantageous to those plants which do not produce nectar and juices.
5)It is more economical as it does not consume energy for large population.
6)Pollen grains are not wasted.
7)Maintains the purity of races from one generation to another as no variation takes place.
DISADVANTAGES OF SELF POLLINATION:
1)The useful characters can not be introduced.
2)The undesirable characters do not eliminate.
3)The offspring are readily susceptible to disease.
4)It does not reveal any variability so they may fail in long run.
5)Continuous self pollination can lead to death of species.
6)No variation are produced as a result of no evolution taken place.
7)Weak progeny are produced.

TERMS USED: GEITONOGAMY:
Pollination between flowers of same plant is called geitonogamy.It may require external agency like insects,winds etc.

XENOGAMY:
Pollination between flowers of different plant is called xenogamy.

2)CROSS POLINATION(ALLOGAMY):
cross pollination is transfer of pollen grains from anther of one flower to stigma of genetically different flower.Cross polination is accompanied with external agencies like wind,water,animals etc.

EXTERNAL AGENCIES THAT BRING CROSS POLLINATION: 1)ANEMOPHILY:
Pollination which takes place by the help of wind is called anemophily.Wind picks up the pollen grains from the dehisced anther of a flower and drops them on the stigma of other flowers.
CHARACTERISTICS:
a)Anemophilous plants grow in large group.This ensures the pollination of flowers of all the plants.
b)In many herbaceous plants the flowers are produced above the fooliage.This ensures the exposure of flowers to the wind.
c)in deciduous anemophilous trees,flowers are produced before leaves(Peach,apple).
d)A high proportion of pollen grains are wasted in wind pollination.Therefore,plants produce large qunatities of the pollen.
e)Pollen grains are small,light or dusty and can be blown to large distances.
f)Pollen grains are light and inwettable.
g)In anemophilous flowers,the non essential floral organs are either absent or reduced.This make the flowers small,inconspicuous and devoid of colour,nectar or smell.

2)HYDROPHILY:
The pollination which takes place by means of water is known as hydrophily.It occurs only in aquatic plants.however,many aquatic plants with emerged flowers have other modes of pollination.
Eg:Lemma,Zostera,Vallisneria
TYPES OF HYDROPHILY:
a)HYPOHYDROPHILY:
It occurs below the surface of water.
Eg:Zostera,Ceratophylum,Hydrilla
b)EPIHYDROPHILY:
It occurs over the surface of water.
Eg:Vallisneria

3)ZOOPHILY:
The pollination which takes place by the means of animal is known as zoophily.It is of different types:
a)ENTOMOPHILY:
The pollination by means of insects is known as entomophily.
CHARACTERISTICS:
i)The flowers are large and bright in colour;and if small,they are grouped into inflorescence.Eg:Marigold
ii)They have scent and nectar.
iii)the pollen grains are large with sticky wall.
iv)Some flowers like violet,pansy and orchids have bright lines and spots on their petals which help the insects to the nectar.

b)ORNITHOPHILY:
Pollination that takes place with the help of birds is known as ornithophily.
Eg:Bombax,Begonia,Butea monosperma(flame of forest)
FEATURES:
i)The flowers produces large amount of nectar.
ii)The corolla is funnel shaped which enable the bird to sip the nectar.
iii)The petals are of bright colour like red so that they can be seen from large distances.
iv)the stigma are sticky.

c)CHIROPTEROPHILY:
The pollination that takes place with the accompany from bat is known as chiropterophily.
Eg:Anthocephalos cadamba
CHARACTERISTICS:
i)The flowers are of dull colour.
ii)The flower consists of large amount of nectars and juices then ornithophilous flowers.
iii)The flower produce large number of stamens.

d)MALACOPHILY:
The pollination that takes place by the support of snail is called malacophily.
Eg:Arisaema(Snake or cobra plant) and arum lilly

DEVICES TO ENSURE CROSS POLLINATION:
1)DECLINY OR UNISEXUALITY:
This is the condition where the plants are dioecious(unisexual)which unable them to cross pollinate.
2)DICHOGAMY:
This is the condition in bisexual flowers where the anthers and stigma mature at different time.Dichogamy is of two types:
a)PROTOGYNY:
stigma matures earlier than anther of same flower.Eg:Mirabilis
b)PROTANDRY:
Anther mature earlier than stigma of same flower.Eg:cotton,sunflower
3)SUPPRESION OF ONE SEX:
In some bisexual flower,one of the two sex organ(either stamen or carpel)is completely suppressed and becomes sterile.
4)PREPOTENCY:
In certain plants pollen grains of one flower germinate on the stigma of another flower more rapidly than the same one.
5)SELF STERILITY:
Pollen grains of a flower are incapable of completing growth on the stigma of same flower due to mutual inhibition.
6)HETEROSTYLY:
This is the condition of occurrence of two or more than two types of flowers which have different lenth of styles and stamens.
Eg:Oxalis(trimorphy),Primula(dimorphic)
7)HERKOGAMY:
In certainn flower there may be some physical barrier between anther annd stigma so that self pollination becomes impossible.
Eg:Calotropis
ADVANTAGES OF CROSS POLLINATION:
1)Useful characters can be introduced in plants.
2)Undesirable characters can be elimated.
3)It increase the adaptability of varieties towarsds the new environment.
4)The seeds produced are usually large and more vigorous.
5)A phenomenon of hybrid vigour can be observed in this method.
6)Seed production never falls below an average minimum.

DISADVANTAGES OF CROSS POLLINATION:
1)It depends on external organisms for pollination to occur.
2)It is less economical.The plant consume large amount of energy in production of large no of pollen grains.
3)Some of very good characters of variety are likely to be spoiled.
4)Due to cross pollination,some undesirable characters can remain in variety.
5)It fails in oxalis.
6)Pollen grains are lost.