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12.4: Self-Pollination and Cross-Pollination - Biology


In angiosperms, pollination is defined as the placement or transfer of pollen from the anther to the stigma of the same flower or another flower. Interestingly, though these two plants appear to be entirely different, the genetic difference between them is miniscule.

Pollination takes two forms: self-pollination and cross-pollination. Self-pollination occurs when the pollen from the anther is deposited on the stigma of the same flower, or another flower on the same plant. Cross-pollination is the transfer of pollen from the anther of one flower to the stigma of another flower on a different individual of the same species. Self-pollination occurs in flowers where the stamen and carpel mature at the same time, and are positioned so that the pollen can land on the flower’s stigma. This method of pollination does not require an investment from the plant to provide nectar and pollen as food for pollinators.

Explore this interactive website to review self-pollination and cross-pollination.

Living species are designed to ensure survival of their progeny; those that fail become extinct. Genetic diversity is therefore required so that in changing environmental or stress conditions, some of the progeny can survive. Self-pollination leads to the production of plants with less genetic diversity, since genetic material from the same plant is used to form gametes, and eventually, the zygote. In contrast, cross-pollination—or out-crossing—leads to greater genetic diversity because the microgametophyte and megagametophyte are derived from different plants.

Because cross-pollination allows for more genetic diversity, plants have developed many ways to avoid self-pollination. In some species, the pollen and the ovary mature at different times. These flowers make self-pollination nearly impossible. By the time pollen matures and has been shed, the stigma of this flower is mature and can only be pollinated by pollen from another flower. Some flowers have developed physical features that prevent self-pollination. The primrose is one such flower. Primroses have evolved two flower types with differences in anther and stigma length: the pin-eyed flower has anthers positioned at the pollen tube’s halfway point, and the thrum-eyed flower’s stigma is likewise located at the halfway point. Insects easily cross-pollinate while seeking the nectar at the bottom of the pollen tube. This phenomenon is also known as heterostyly. Many plants, such as cucumber, have male and female flowers located on different parts of the plant, thus making self-pollination difficult. In yet other species, the male and female flowers are borne on different plants (dioecious). All of these are barriers to self-pollination; therefore, the plants depend on pollinators to transfer pollen. The majority of pollinators are biotic agents such as insects (like bees, flies, and butterflies), bats, birds, and other animals. Other plant species are pollinated by abiotic agents, such as wind and water.


Class 12 Biology Chapter 2 Pollination

Pollination refers to the method where pollen grains are transferred from the anther of one plant to the stigma of the other plant. The pollen grains are present in the anther of the plant which contains male gametes. The seeds of the flowering plants carry the genetic information of the parent plant and grow into a new plant. In flowering plants, pollination is the first process of sexual fertilization. In the rest of the article, we will take a look at the process of pollination, main types of pollination, advantages and disadvantages of each type and environmental impacts. 

The chapter Pollintion is covered under unit 1, Reproduction of NCERT Class 12 Biology. The topic has been included in the syllabus for the session 2020-21. In the revised syllabus of CBSE, no topics have been omitted from this portion. The whole unit, i.e, Unit 1 will carry around 14 marks in the board examination.

Define Pollination

Pollination is a process of transferring pollen grains from the anther which is the male part of a flower to the stigma (female part). In this process the plants can produce seeds for the next generation. For successful pollination, the same species of flower are necessary.

Figure: Pollination, Structure of a flower

Process of Pollination

There are three stages in pollen germination. These are hydration, activation and pollen tube emergence. The pollen grain is strictly dehydrated so that it is easily transported from flower to flower. After rehydration, germination takes place. Hydration permits the pollen grain&aposs plasma membrane to reform into an effective osmotic membrane. Activation engages the development of filament throughout the cytoplasm of cells. The pollen tube grows as the hydration and activation spreads. In flowering plants, the anthers generate microspores by meiosis. This causes mitosis to create male gametophytes. On the other hand the ovules produce megaspores by meiosis. When a pollen grain sticks to the stigma, it germinates and develops a pollen tube which grows through the tissues of the style. When the tube arrives at the egg sac, two sperm cells go into the female gametophyte and fertilisation takes place.

Types of Pollination

Flowering plants completely depend on pollination methods for reproduction. There are two types of pollination -

Self Pollination

It is a primary type of pollination and needs a single flower. Self Pollination happens when pollen grains directly fall from another into the stigma of the flower. This method is smooth and it causes reduction in genetic diversity as the flower&aposs sperm and egg cells impart some genetic information.

ਏigure: Self Pollination

Advantages and Disadvantages of Self- pollination

Advantages - 

  • Self Pollination confirms that recessive characters are extracted.
  • In self pollination, the wastage of the pollen grains is less than cross Pollination.
  • In this case, purity of race is retained as in the genes there is no diversity.
  • In self pollination, there are no external factors like wind, water etc.
  • Self pollination proves that even a lower quantity of produced pollen grains from plants is a successful pollination process.

Disadvantages - The main disadvantage of self pollination is that mixing up of genes does not happen here as - 

  • There is a reduction of vigour and vitality of the race.
  • Among the offsprings, there is also the reduction of immunity to diseases.

Cross-Pollination 

It is an intricate type of pollination that makes the transfer of pollen grains from the anther of the flower into the stigma of another flower. In this process, there is an increase in genetic diversity as different flowers share and combine genetic information to make unique offspring.

Figure: Cross Pollination

Types of Cross Pollination

In the process of cross pollination, there needs the help of biotic and abiotic factors like - water, wind , insects, birds, animals etc.

Pollination by wind

Some flowers with the characteristics of greenish, small and odourless use wind pollination. Energy of these flowers is not used for making colourful petals. This type of Pollination happens as plants lack flowers with nectar. The male parts of the anemophilous flowers produce very large quantities of pollen and the stigma and the female reproductive parts of a flower are very large, sticky and feathery. Some examples of wind-pollinated plants are palm, maize, coconut, grasses etc.

Figure: Wind Pollination

Pollination by Animals

Animals take an important role in the reproduction of plants. They assist in seed dispersal. Animals move to different locations at the time of eating fruits of plants. This action helps in spreading the seeds and through this process new plants are born.

Artificial Pollination

Artificial Pollination is made by human beings. This process is also named anthropophily. If there are problems in the pollination by biotic and abiotic agents, the artificial process of pollination is followed by spreading pollen grains over the female flowers. In this process, hybridisation techniques are used.

Figure: Artificial Pollination 

Advantages and disadvantages of Cross-Pollination
  • Here the qualities of seeds are good in vigour and vitality.
  • By the process of cross Pollination unisexual plants can reproduce.
  • As a result of genetic recombination the recessive characters are eliminated.
  • Through this process the baby plant&aposs immunity level increases.
  • Cross Pollination makes new genes as there is mainly fertilisation between genetically different gametes.

Disadvantages

  • There is huge wastage of pollen grains.
  • At the time of genetic recombination, there are chances of removal of good qualities and additions of unwanted features in new generations.

Environmental Impacts

Nowadays, pollinator decline is noticed on a large scale. This causes an inconvenience in plant regeneration as - seed dispersal, pollination. In the reproduction process plant - animal interaction is very necessary and as it lacks, there is a huge threat in biodiversity and ecosystem. Some causes of pollinator decline are use of pesticides, habitat destruction, parasitism, climate change etc. Some more destructive forms are selective logging, fragmentation, conversion to secondary forest habitat. Climate change causes a pollinator crisis which affects the crops production. Insecticides like neonicotinoids affect the bees and many researchers believe that it is intensely detrimental for the population of pollinators. Due to the imbalance in ecosystems for pollinators decline there is also the collapse of food security.

Check this, for more information.

Sample Questions on pollination

Ques. What are pollinators?

Ans. Pollinators are insects , birds that move pollen from one plant to another. It is done when they are on nectar or pollen.

Ques. Mention the names of pollinators.

Ans. Names of some pollinators are butterflies, birds, bees, bats etc.

Ques. What role do the pollinators play?

Ans. The pollinators move pollen from the male part to the female part of the plant. Pollinators are very important parts to produce seeds, fruits in some plants.

Ques. What attracts pollinators to a plant?

Ans. Nectar, pollen, color, scent attract pollinators to a plant.

Ques. What kinds of bees pollinate crops?

Ans. Managed and wild bees can pollinate crops. In most commercial farms, the European honey bees are the main pollinators.

Ques. Is it safe to spray during bloom?

Ans. When bees are active in fields, the crops bloom. It is good to avoid spraying during bloom.

Ques. why is the diversity of pollinators important?

Ans. Richness of species and pollinators strengthen effective crops. It also confirms the enhancement of quantity and quality of crops.

Previous Years’ Questions

Very Short Answer Questions (1 mark)

Ques. What do you mean by pollen- pistil interaction and how is it mediated? (Foreign 2014)

Ans. Pollen- pistil interaction refers to a chain or group of events that takes place due to the falling of pollen over the stigma and the formation of pollen tube and its entry into the ovule. It is basically a phenomenon of acceptance or rejection of pollen grains by the pistil (stigma) which is mediated by chemical components of pollen grains and interacting with that of pistil.

Ques. Differentiate between xenogamy and geitonogamy? (Delhi 2014c)

Ans. Xenogamy is the process by which pollen grains are transfered from anther of one flower to stigma of another flower of a different plant. While, geitonogamy is the transfer of pollen grains from the anther of one flower to the stigma of another flower on the same plant. 

Ques. How do the pollen rains of Vallisneria protect themselves? (All India 2012)

Ans. The pollination of Vallisneria takes place by means of water, therefore in this case, the pollen grains are covered by mucilaginous coating that protects them.

Ques. Name the type of flower that favours cross-pollination. (All India 2009)

Ans. The type of flower that favours cross-pollination is Chasmogamous flowers which are similar to the other species with exposed anthers and stigma.


Short Answer Questions (2-3 marks)

Ques. Explain: in angiosperms, zygote is diploid while whereas primary endosperm cell is triploid. (All India 2013)

Or, Mention the reasons for the difference in ploidy of zygote and primary endosperm nucleus in an angiosperm. (Delhi 2010)

Ans. In the angiosperms or the flowering plants, one of the male gametes fuses with egg cell which results in the formation of zygote. Thus, zygote is diploid. Whereas, primary endosperm cell is triploid because the nucleus of the second male gamete fuses with the two haploid polar nuclei or diploid secondary nucleus of the centrl cell to form a triploid primary endosperm nucleus. The central cell is now called primary endosperm cell. 

Ques. Write one advantage and one disadvantage of cleistogamy. (All India 2012)

Ans. The advantage and disadvantage are as follows:

Advantage –਌leistogamousਏlowers produce assured seed-set even in the absence of pollinators.

Disadvantage –਌leistogamousਏlowers are invariably autogamous therefore, there is no chanse of cross-pollination. 

Ques. Why should a bisexual flower be emasculated and bagged before artificial pollination? (Foreign 2010)

Ans.਎masculation in a bisexual flower is required in order to prevent the contamination of stigma with self pollen grains. Bagging is done to prevent contamination of stigma of the emasculated flower with any other unwanted pollen grains. This is the reason why a bisexual flower should emasculated and bagged prior to artificial pollination.

Ques. Differentiate the wind pollinated and insect pollinated flowers. Give an example of each type. (Foreign 2014)

Ans. The differences between the wind pollinated and insect pollinated flowers are,


Self Pollination and Cross Pollination | Plants

Read this article to learn about Self Pollination and Cross Pollination. After reading this article you will learn about 1. Method of Self Pollination 2. Method of Cross Pollination 3. Mechanism of Self Pollination 4. Mechanism of Cross Pollination.

Methods of Self Pollination:

Always based on phenotype Individual plants are selected and next generation continued from seeds of selected plants. Rouging or uprooting of undesirable plants and harvesting of remaining plants in mass.

(ii) Pure line selection method:

Concept of pure line was given by – Johnson. Pure line is a progeny of single homozygous, self pollinated crops. Large number of plants are selected from self pollinated crop and tested or evaluated separately & the best progeny (plant) released as pure line varieties. All plants of pure line variety are homozygous due to some genotype.

Individual plants are selected from F2 generation and the subsequent generation & their progeny are tested. During entire operation, a record of all parents’ offspring relationship is kept.

1. Most commonly used method for selection from segregation generations of crosses in self pollinated crops.

2. Useful in selection of new superior recombinant types.

3. Suitable for improving specific traits i.e. plant height, disease resistance, maturity time etc.

(iv) Single seed descent method:

First applied in oat in 1965 by Graphius Single seed descent method continues from F2 to F5/F6 generation in which superior single plants are finally selected, harvested and growing one seed from each plant.

1. Used to improve one or two specific defects of a high yielding variety.

2. Commonly used for transfer of disease resistance from one variety to another variety.

1 st used by Nilson Ehle, 1908

F1 and the subsequent generations are harvested in bulk or mass to rise the next generation. At the end, single plant is selected and tested same as pedigree method.

1. Methods used for handling the segregating generation – Pedigree, Bulk & Single seed descent method.

Methods of Cross Pollination:

1. 1 st used by Hopkins in 1908

2. Also known as Ear to row method of selection.

1. Superior phenotypic selection of 50-100 plants & open pollination in between them and then individual plant seed harvested.

2. Single row of 10-15 plants from each selected plants grown (progeny row). They evaluated for desirable traits and superior progeny are identified.

3. Superior phenotypic plants are selected from superior progeny and allowed to open pollinated.

4. Small progeny row grown (same as in 2) from selected plants and the process repeated.

(iii) Recurrent selection:

Recurrent selection is a method in which desirable scattered favourable genes are selected in different plants in each generation.

(iv) Hybrid varieties:

1 st commercially exploited into maize

Hybrid or F1 are the seed as well as the progeny resulting from hybridization (A x B).

Single cross A x B = F1 (Hybrid)

Double cross → (A x B) x (C x D) = Two single cross

Three way cross → (A x B) x C i.e. Ganga Safed-2 variety of maize (OP.)

Double to cross A single cross (A x B) x OP. variety

Top cross → selected variety/line/clone x open pollinated variety

Intraspecific/inter-varietal Hybrid:

A hybrid between genetically deferent genotypes of the same species. Ex. H4, H6, H8, HIO varieties of cotton

Interspecific/intra-generic Hybrid: The F1 progeny (hybrid) between two different species of the same genus. Ex. Varalaxmi (G. hirsutum x G. barbadense) DCH 32, HB 224 varieties of cotton.

(v) Synthetic varieties:

Synthetic variety is produced by crossing in all combinations a number of lines that combine well each other.

It is produced by mixing the seeds of several phenotypically outstanding lines (varieties) and encouraging open pollination to produce crosses in all combinations among the mixed lines. These varieties are similar in maturity, height, seed size, seed colour etc.

Mechanism of Self Pollination:

(i) Chasmogamy: Flowers open but only after pollination has taken place, ex. rice, moong, oat etc.

(ii) Cleistogamy – Flowers do not open at all ex. wheat, barley etc.

Mechanism of Cross Pollination:

(i) Dicliny – flowers are either staminate (male) or pistilate (female)

(ii) Dichogamy – male and female flowers of a hermaphrodite flowers matures at different time.

1. Protogyny →Gynus = female, female matures before male i.e. Bajra

2. Protondry →Andrus = male, male matures first i.e. Maize

(iii) Geitonogamy: Pollen from a flower of one plant falls on the stigmas of other flowers of the same plant, ex. Maize

(iv) Monocius: Male (staminate) and female (pistilate) flowers occur on the same plant ex. Maize, castor, coconut, colorcasts etc.

(v) Diocius: Male and female flowers occur on different plants ex. Papaya, datepalm etc.

(vi) 1 st Inter-generic hybrid: Raphino brassica (Radish x Cabbage) – developed by Karpencheko, 1927

(vii) For hybrid variety release, we use:

(viii) Koelreuter carried out hybridization experiments in tobacco in between 1760-1766.

(ix) The first artificial plant hybrid was produced by the crossing between carnation and sweet William by Thomas Fairchild.

(x) Heterosis: Superiority of F1, hybrids over both of its parents.

When the heterosis is estimated over the mid parent, i.e. mean or average value of two parents

Exchange of chromatin between non-sister chromatids of homologous chromosomes. It releases genetic variability by forming new gene combinations.

(xii) Inbreeding Depression (ID):

Loss or decrease in vigour and fitness as a result of inbreeding. Degree of inbreeding depression is:

1. High I.D. – Alfalfa, Carrot etc.

2. Moderate I.D. – Maize, Sorghum, Bajra etc.

3. Low I.D. – Onion, Cucurbits, Sunflower etc.

4. No LD.-Self pollinated species.

1. Sudden heritable change in any characteristics of an organism.

2. Mullar first used X-rays as mutagen.

3. Natural mutation is of low frequency 10 -6

4. Muton is the unit in which mutation occurs.

Mutagens are the chemicals or physical agents which greatly enhance the frequency of mutation.

Some commonly used mutagens are:

(a) Physical mutagens: X-rays, Gama rays, Alfa particles, Bita particles etc.

(b) Chemical mutagens: Ethyl methane sulphonate. Methyl methane sulphonate, Nitrous acid, 5 Bromo Uracil etc.

A condition in which either pollen is absent or non functional in flowering plants.

Types of Male Sterility:

1. Genetic Male Sterility (GMS)-Pollen sterility, caused by nuclear genes.

2. Cytoplasmic Male Sterility (CMS) – Pollen sterility, caused by cytoplasmic genes.

3. Cytoplasmic Genetic Male Sterility (CGMS) – Caused by cytoplasmic & nuclear genes.

4. Chemically induced Male Sterility- induced by various chemical called Male Gametocytes.

5. Transgenic Male Sterility (TMS) – Induced by the technique of genetic engineering.

Plants in which specific foreign(s), isolated from diverse biological systems, viz. fungi, bacteria, virus, plants or animals has/have been transferred genetic engineering and stable integrated into their genomes, and the transferred genes are able to perform their specific functions.

(xvi) Norin 10 and Tom Thumb are the source of reduced height (rht) genes used in wheat breeding.

(xvii) Triticale is a man made cereal, usually hexaploid species and has the genomic constitution AABBRR.

The cultivated banana is auto triploid.

(xviii) De-tasseling: Removal of the entire tassel (male inflorescence of maize) from the plant before pollen to initiate cross hybridization.

(xix) Drosophila melanogaster (organism) is regarded as the “Queen of Genetics”.

(xx) Agrobaderium is called as natural genetic engineer.

(xxi) Brassica triangle: ‘U’s triangle given by U. Nagaheru (1935).


How Does Pollination Work?

There are different ways pollination can occur. Depending on what type of plant is pollinated, the process will vary. Here is how they each work:

Regular Pollination

Typical pollination happens when one plant gives pollen to another plant. One of the plants must have the male plant sex organ known as the stamen. The other plant must have the female sex organ known as the stigma.

When the wind blows, or an insect collects pollen from the male plant, it allows the pollen to transfer to the female plant.

Realize when the wind blows, pollen is scattered in the air. This allows the pollen to land inside the female flower.

But when a bee lands inside a flower, it will get pollen on it. When the bee lands on the next flower, the pollen collected from the previous flower will fall off into the new flower. If the flower is female, pollination has occurred.

Self-Pollination

Some plants pollinate differently. There are some plants such as tomatoes, pumpkins, cucumbers, and squash which produce both male and female flowers on the same plant.

For these plants to be pollinated, the wind has to blow, or a bee has to land in a male flower, and the pollen has to either be blown into the female flower or be transferred to the female flower by an insect.

If the pollen has been transferred from a male flower to a female flower of the same kind, fruit will develop on the plant.

What About the Plants That Don’t Pollinate?

Every plant could be pollinated, but there are some plants you don’t want to pollinate. For instance, lettuce is a plant you don’t want to pollinate. The reason is you want to eat lettuce before it ‘bolts.’

Bolting is when the plant is getting ready to make seeds. We prefer to eat lettuce before bolt happens. It is most common for bolt to take place when the weather begins to warm up towards the end of lettuce’s growing season.

However, if the lettuce bolts, all the plant’s energy will go into making seeds to carry on with the next generation.

When this happens, the leaves will become tough and bitter. It is not a desirable flavor, which is why most gardeners try to prevent bolting and pollination in crops where you eat the plant itself.



The transfer of pollen grains from the stigma of a pistil is known as Pollination. Pollination in flowering plants occurs by two methods- self-pollination and cross-pollination.

Self Pollination - Self Pollination involves the transfer of pollen grain from the anther to the stigma of the same flower or genetically similar flower. It is of two types -

Autogamy - Transfer of pollen grains from the anther to the stigma of the same flower is known as Autogamy. It occurs by the three methods - Self Pollination showing by A& B and cross-pollination is shown by B & C

  • Cleistogamy - Some Plants never open to ensure complete self-pollination. This condition is called Cleistogamy. For example - oxalis, viola.
  • Homogamy - Anther and stigma of the bisexual flower of the same plants mature at the same time. This condition is called Homogamy. For example - Mirabilis, potato, sunflower, etc.
  • Bud Pollinatiton - Anther and stigma of the bisexual flowers of some plants mature before the openings of the buds to ensure self-pollination. For example - wheat, rice, pea.

Geitnogamy - When anther of one flower is transferred to the stigma of another flower borne on the same plant, then this condition is known as Geitonogamy.

Advantage Of Self - Pollination -

  • Chances Of Pollination are more.
  • Self Pollination maintains the purity of race and avoids mixing.
  • It needs not to produce a large number of pollen grains.

Disadvantage Of Self - Pollination -

  • No possibility of the introduction of new desirable characters.
  • Undesirable characters can not be eliminated.
  • It does not help in evolution.

Cross- Pollination - Transfer of pollen grains from the flower of one plant to the stigma of another plant flower, is known as Cross-Pollination or Allogamy.

  • Xenogamy - The pollination in which the pollen grains of one flower transferred to the stigma of another flower of the same species is known as Xenogamy.

Adaptations Of Cross-Pollination -

  • Monoecious - When male and female part of the flower present at the same time then this condition is called Monoecious. For example - Maize, castor.

  • Protandry - The conditions in which the anther part mature earlier than the carpels. For example -Sunflower.


Cross-pollination

The transfer of pollen grains form the anther of one flower to the stigma of another flower belonging to the same species or closely allied species is called cross-pollination or Allogamy. When the pollination takes place between two flowers of the same species, it is called xenogamy, while if it occurs between two closely related species, it is called hybridism.

What are the Characteristics of cross-pollination?

Cross pollination by insect

Cross-pollination usually occurs in plants having unisexual flower. It may also occur in flowers showing male sterile lines e.g. maize, Solanum. Flowers showing different maturation times for stamens and carpels may also show cross-pollination, e.g. sunflower, Magnolia. It may be in bisexual flowers with differential stamens and carpels, commonly known as heteromorphisme.g. Oxalis. Some flowers, where a barrier is created between stamen nd carpel also shows cross-pollination e.g. Iris. The flowers showing different genetic makeup are showing the cross-pollination.

Adaptations for cross-pollination:

a) Dicliny or Unisexuality: In unisexual flowers, self-pollination is impossible, so cross-pollination is observed e.g. gourd.
b) Self-sterility : In certain flowers, the pollen grains are sterile in nature due to male sterility and hence they cannot fertilize the egg of the same flower, so they depend on the pollen grains of another flower coming via cross-pollination, e.g. Solanum maize.
c) Dichogamy: The androecium and gynoecium of a bisexual flower do not mature at the sametime, so self-pollination can never take place and they are of two types: Protandry (The anther matures earlier than the stigma, e.g. sunflower) and Protogyny (The stigma matures earlier to anther, e.g. Polyalthia).


d) Herkogamy: In this case, self-pollination is impossible, because some of the floral parts act as a physical barrier between anther and stigma and thus cross-pollination is favoured. In Iris flower, the anthers are extrorse and they are concealed by overlapping or overarching of the petaloid style, which conceals the anther, making self-pollination impossible.
e) Heteromorphism: The flowers of one single species may vary on the basis of the forms of stamens and carpels and accordingly, the flowers may be dimorphic or trimorphic in nature.
f) Homomorphicself incompatibility: It is a rare type of self incompatibility, in which stamens and pistil do not vary in size, but even than, the pollen grains are rejected by the stigma of the same flower. It is found in Oenothera, Aster.

Methods of Cross-Pollination

There are various types of cross-pollination and the agents are discussed below:

1. Anemophily:

When pollination is brought upon by wind, it is called anemophily and the flowers are called anemophilous, e.g. paddy, wheat, maize, grasses.
Adaptations of wind-pollinated flowers : These types of flowers show the following characteristics: -
i) The flowers are small and not easily seen.
ii) The petals are not colored and they are not scented i.e., devoid of osmophores.
iii) They are without nectaries.
iv) The flowers are aggregated on a long peduncle above the vegetative parts, which makes the process of wind-pollination easy.
v) The sepals and petals are small and not easily seen and sometimes, undifferentiated to form perianth.
vi) The accessory whorls do not cover the sexual reproductive organs.
vii) The stamens are provided with long filaments with versatile anthers, which are easily cut off by air current.
viii) The pollen grains are small, granular, light weight, dry and shaped in huge quantity.
ix) The style is also long and that helps in the protrusion of the stigma from the flower.
x) The stigma is large, feathery and branched, which helps in easy trapping of the pollen grains.

2. Hydrophily

When the cross-pollination in a flower takes place with the help of water, it is called hydrophilous and the phenomenon is termed as hydrophily. The water pollinated plants are of two types :
i) Hypohydrogamous: The pollination taking place in completely submerge condition under water e.g. Ceratophyllum.
ii) Epihydrogamous: The pollination taking place along the surface of the wateje.g. Vallisneria, Hydrilla.

Adaptations for water-pollinated flowers

The hydrophilous flowers show the following characteristics :
i) The flowers are small, inconspicuous, light in weight, helping in floatation.
ii) The flowers are not showy, without coloured petals, without any fragrance.
iii) The floral parts are covered with waxy substance or cutin, which prevent them from getting damaged by water.
iv) The accessory whorls, calyx and corolla are small, so the essential floral whorls or androecium and gynoecium are always exposed in water current.
v) The dehiscence of anther is rapid and so the pollen grains are scattered in wider areas in a short time.
vi) The pollen grains are small, light in weight, impervious to water and hence carried by water to long distances.
vii) The female flowers usually have a short coiled stalk, that reach the water surface by uncoiling.
viii) The stigma is provided with bristles, which can easily trap the pollen grains floating in water.
ix) The coiled stalk of female flower may recoil again after pollination.

Method of pollination

In hypohydrogamousflowers like Ceratophyllum, the flowers never comes above the water surface, the male flowers have superior position, which drop the pollen-grains (impervious to water) on to the stigma of the female flower remaining below. The epihydrogamousflowers are always at the water surface, so pollination is always brought about on the water surface, where pollen grains are carried by the water-current from the male flower, up to the stigma. Some flowers, like that of Vallisneria, the flowers usually remain submerged. The small .male flowers on maturity get detached from the spadix and float on the water surface on a boat-like spathy bract. The coiled stalk of the female flower uncoils and the female flowers come to the water surface, their stigmas come in contact with the anthers of the male flower and pollination takes place. After pollination, the stalk of the female flowers recoil again and the flowers again go down underwater.


What is difference between self pollination and cross pollination

There are following difference between self pollination and cross pollination given in the following table:-

Self pollination:
1) It is Migration of pollen grains from anther to stigma of same flower or another flower which are born on same plant.

2) if the Pollen transferred within same flower anther to stigma,there is no need of external agency in self pollination. if the Pollen Grain transferred from one flower to another flower which are born on same plant need external agency for their transferred. external agency like wind and touch help in self pollination.

3) Both anthers and stigma of a flower or another flower which are born on same plant mature almost at same time.

4) it is occurs in closed flower that is known as cleistogamous flower, race is almost constant homozygous and it give rise to pure lines and in preserve the parental characters.

5) origin of new species in self pollination is not possible because genetic material exchange within same trait within flower, genetic diversity and evolution not taking place if flower is self pollinated.

Cross pollination:-
1) Migration of pollen grains from anther to stigma of another flower which is born on different plant.

2) cross pollination always occurs through and help of external agency like air, wind, insect, etc. in absence of external agency cross pollination does not takes place.

3) in cross pollinating flower anther and stigma mature at different time.

4) cross pollination occurs only when the flower are open, the race is changing, it is heterozygous, it gives rise to offspring having variation and different diversity, it does not preserve the parental character.

5) cross pollination help in giving rise to new races and variety, so evolution and Diversity lead to formation of new species. So there is possibility of evolution of new species in cross pollination.


12.4: Self-Pollination and Cross-Pollination - Biology

In angiosperms, pollination is defined as the placement or transfer of pollen from the anther to the stigma of the same flower or another flower. In gymnosperms, pollination involves pollen transfer from the male cone to the female cone. Upon transfer, the pollen germinates to form the pollen tube and the sperm for fertilizing the egg. Pollination has been well studied since the time of Gregor Mendel. Mendel successfully carried out self- as well as cross-pollination in garden peas while studying how characteristics were passed on from one generation to the next. Today’s crops are a result of plant breeding, which employs artificial selection to produce the present-day cultivars. A case in point is today’s corn, which is a result of years of breeding that started with its ancestor, teosinte. The teosinte that the ancient Mayans originally began cultivating had tiny seeds—vastly different from today’s relatively giant ears of corn. Interestingly, though these two plants appear to be entirely different, the genetic difference between them is miniscule.

Pollination takes two forms: self-pollination and cross-pollination. Self-pollination occurs when the pollen from the anther is deposited on the stigma of the same flower, or another flower on the same plant. Cross-pollination is the transfer of pollen from the anther of one flower to the stigma of another flower on a different individual of the same species. Self-pollination occurs in flowers where the stamen and carpel mature at the same time, and are positioned so that the pollen can land on the flower’s stigma. This method of pollination does not require an investment from the plant to provide nectar and pollen as food for pollinators.

Living species are designed to ensure survival of their progeny those that fail become extinct. Genetic diversity is therefore required so that in changing environmental or stress conditions, some of the progeny can survive. Self-pollination leads to the production of plants with less genetic diversity, since genetic material from the same plant is used to form gametes, and eventually, the zygote. In contrast, cross-pollination—or out-crossing—leads to greater genetic diversity because the microgametophyte and megagametophyte are derived from different plants.

Because cross-pollination allows for more genetic diversity, plants have developed many ways to avoid self-pollination. In some species, the pollen and the ovary mature at different times. These flowers make self-pollination nearly impossible. By the time pollen matures and has been shed, the stigma of this flower is mature and can only be pollinated by pollen from another flower. Some flowers have developed physical features that prevent self-pollination. The primrose is one such flower. Primroses have evolved two flower types with differences in anther and stigma length: the pin-eyed flower has anthers positioned at the pollen tube’s halfway point, and the thrum-eyed flower’s stigma is likewise located at the halfway point. Insects easily cross-pollinate while seeking the nectar at the bottom of the pollen tube. This phenomenon is also known as heterostyly. Many plants, such as cucumber, have male and female flowers located on different parts of the plant, thus making self-pollination difficult. In yet other species, the male and female flowers are borne on different plants (dioecious). All of these are barriers to self-pollination therefore, the plants depend on pollinators to transfer pollen. The majority of pollinators are biotic agents such as insects (like bees, flies, and butterflies), bats, birds, and other animals. Other plant species are pollinated by abiotic agents, such as wind and water.


DIAGRAM & FLOWCHART

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Self Pollination And Cross Pollination By Lakshya Kumar Rai