BiologyCBSE Class 12 · Sexual Reproduction in Flowering Plants

Pollination and Outbreeding Devices

Updated 15 October 2026 · Fact-checked

Pollination is the transfer of pollen grains from an anther to a stigma. It may be autogamy (same flower), geitonogamy (another flower of the same plant) or xenogamy (another plant). Because continued self-pollination causes inbreeding depression, plants use outbreeding devices: timing differences, separated anther and stigma, self-incompatibility and unisexual flowers.

Understand Pollination and Outbreeding Devices

Why pollination matters. Male and female gametes are both non-motile in flowering plants, so pollen has to be carried to the stigma before fertilisation can happen.

Three kinds of pollination (by the source of pollen):

Autogamy: pollen to the stigma of the *same flower*. Needs anthers and stigma to mature together and lie close. In chasmogamous flowers (open, with exposed anthers and stigma) complete autogamy is rare. Cleistogamous flowers never open, so they are invariably autogamous and set seed even without pollinators. Viola (pansy), Oxalis and Commelina bear both kinds of flowers. Drawback: cleistogamy cannot bring in new genes.
Geitonogamy: pollen to *another flower of the same plant*. It is functionally cross-pollination (an agent carries the pollen) but genetically like autogamy, because the pollen comes from the same plant.
Xenogamy: pollen to the stigma of a *different plant*. The only kind that brings genetically different pollen to the stigma.

Agents of pollination.

Wind (common in grasses): light, non-sticky pollen; well-exposed stamens; large, often feathery stigmas to trap pollen; often a single ovule per ovary and many flowers packed into an inflorescence. In a corn cob the 'tassels' are the stigmas and styles that wave in the wind.
Water (rare, about 30 genera, mostly monocots): Vallisneria and Hydrilla in fresh water, Zostera (seagrass) in the sea. In Vallisneria, female flowers reach the surface on long stalks and male flowers or pollen float on the surface to them. In seagrasses, female flowers stay submerged and the long, ribbon-like pollen is carried inside the water. A mucilaginous coat protects such pollen from wetting. Not every water plant uses water: water hyacinth and water lily flowers rise above the surface and are pollinated by insects or wind.
Wind- and water-pollinated flowers are usually not colourful and have no nectar.
Animals (most flowering plants): bees (the main pollinators), butterflies, flies, beetles, wasps, ants, moths, birds such as sunbirds and hummingbirds, bats, and even some primates, rodents and lizards. Insect-pollinated flowers are large, colourful, fragrant and rich in nectar; small ones are clustered into an inflorescence. Flowers visited by moths and bats at night are often pale but fragrant. Rewards are nectar and pollen; some plants offer a safe place to lay eggs (Amorphophallus, whose flower is about 6 feet tall; the yucca plant and its moth cannot complete their life cycles without each other). In some orchids, a male insect mistakes the flower's pattern for a female and pollinates it while trying to mate (pseudocopulation). Pollen and nectar robbers take rewards without pollinating.

Outbreeding devices. Most flowers are bisexual, so self-pollen keeps landing on the stigma. Continued self-pollination leads to inbreeding depression. Devices that favour cross-pollination:
1. Timing: pollen release and stigma receptivity are not synchronised (anthers ripen before the stigma, or the other way round). This is called dichogamy.
2. Position: anther and stigma are placed at different positions, so self-pollen cannot reach the stigma easily.
3. Self-incompatibility: a genetic mechanism that stops self-pollen (from the same flower or other flowers of the same plant) fertilising the ovules, by blocking pollen germination or pollen tube growth in the pistil.
4. Unisexual flowers: on the same plant (monoecious, e.g. castor, maize) they prevent autogamy but not geitonogamy; on separate plants (dioecious, e.g. papaya) they prevent both.

Pollen-pistil interaction. The pistil can recognise whether pollen is compatible (right type) or incompatible. This works through a continuous dialogue between pollen and pistil mediated by chemical components of the two. Compatible pollen germinates and puts out a pollen tube through a germ pore; the tube grows through the stigma and style to the ovary, enters the ovule through the micropyle, and enters a synergid, guided by the filiform apparatus. Incompatible pollen is blocked at germination or tube growth.

Flow chart: pollen lands on stigma → recognition (compatible?) → germination through germ pore → tube through style → ovary → micropyle → synergid (filiform apparatus) → male gametes released.

Artificial hybridisation. A breeder wants only the chosen pollen on the stigma.
1. Emasculation: if the female parent has bisexual flowers, remove the anthers from the flower bud with forceps *before the anthers dehisce*.
2. Bagging: cover the emasculated flower with a bag (often butter paper) to keep unwanted pollen out.
3. When the stigma becomes receptive, dust it with pollen collected from the chosen male parent.
4. Re-bag the flower and let the fruit develop.
If the female parent has unisexual flowers, emasculation is not needed: the female buds are simply bagged before they open.

Draw and label: the three kinds of pollination. Checklist: plant A with two flowers, plant B with one flower; an arrow within one flower of A (autogamy), an arrow between the two flowers of A (geitonogamy), an arrow from a flower of A to the flower of B (xenogamy). Labels: anther, stigma, autogamy, geitonogamy, xenogamy.

Pollination and Outbreeding Devices: key facts

Kinds of pollination: $autogamy (same flower) ∣ geitonogamy (same plant) ∣ xenogamy (another plant)$; Only xenogamy brings genetically different pollen.
Which device stops what: $monoecious: stops autogamy only; dioecious: stops autogamy and geitonogamy$; Castor and maize are monoecious; papaya is dioecious.
Wind-pollinated flower: $light, non-sticky pollen + exposed stamens + large feathery stigma$; Often one ovule per ovary and many flowers in an inflorescence.
Artificial hybridisation sequence: $select parents \to emasculate \to bag \to dust pollen \to re-bag$; Skip emasculation if the female parent bears unisexual flowers.
Pollen tube route: $stigma \to style \to ovary \to micropyle \to synergid$; Filiform apparatus guides the tube into the synergid.

How to answer Pollination and Outbreeding Devices questions

Most questions describe a flower or a breeding situation and ask you to name, explain or suggest. Work from what the feature prevents or allows.

1Identify where the pollen comes from: same flower, another flower of the same plant, or another plant. Name the kind of pollination.
2For a flower description, match features to an agent: exposed stamens and feathery stigma → wind; mucilage-coated pollen on the water surface → water; bright colour, scent, nectar → animals; pale but fragrant → night pollinators.
3For an outbreeding device, state the feature, then what it prevents (autogamy, geitonogamy or both), then the gain (cross-pollination, avoiding inbreeding depression).
4For artificial hybridisation, write the steps in order and say why each is needed (emasculation stops self-pollen; bagging stops foreign pollen).
5For assertion-reason items on pollen-pistil interaction, remember the dialogue is chemical, not electrical.
6In 'suggest' questions, check the flower type first: bisexual → emasculate and bag; unisexual → only bag the female flower.

Pollination and Outbreeding Devices in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Artificial hybridisation and outbreeding devices

Suppose a breeder wants to cross a tomato variety with good flavour (female parent) with a disease-resistant variety (male parent). Tomato has bisexual flowers. A second breeder wants to cross two papaya varieties.

List the steps the tomato breeder must follow and explain why the papaya breeder can skip one of them.

Try it first, then show the solutionSolution

Tomato: choose the parents; remove anthers from flower buds of the flavour variety before they dehisce (emasculation), so its own pollen cannot reach the stigma.
Cover the emasculated buds with butter-paper bags so no stray pollen lands on them.
When the stigma is receptive, dust it with pollen from the disease-resistant variety, then re-bag the flower until the fruit sets.
Papaya is dioecious: female plants bear only female flowers, so there are no anthers to remove; the breeder only bags the female buds before they open and dusts them later.

Answer: Tomato: emasculate, bag, pollinate with chosen pollen, re-bag. Papaya: no emasculation needed (unisexual female flowers); just bag, pollinate and re-bag.

Memory hook: Bisexual flower: remove, bag, dust, bag. Unisexual female: just bag, dust, bag.

Tricks to remember Pollination and Outbreeding Devices

Short memory aids. Say each one aloud once, then use it on a question the same day.

A-G-X: self to stranger
Auto = my own flower; Geitono = my neighbour flower on the same plant; Xeno = a stranger plant.
Use it when: Naming the kind of pollination quickly.
Geitonogamy is a disguised self
It travels like cross, but its genes are self.
Use it when: Explaining why geitonogamy is functionally cross but genetically self-pollination.
T-P-S-U
Timing, Position, Self-incompatibility, Unisexual flowers: four outbreeding devices.
Use it when: Listing outbreeding devices in a 3-mark answer.

Pollination and Outbreeding Devices: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Geitonogamy, both ways · 2 marks · Very short answerBoard level

Geitonogamy can be compared with cross-pollination as well as with self-pollination. Justify. (A question of this kind appeared in the 2027 sample paper.)

Try it first, then show the solutionSolution

Like cross-pollination, it needs a pollinating agent to carry pollen from one flower to another flower (1 mark).
Like self-pollination, the pollen comes from the same plant, so it is genetically identical and brings no new variation (1 mark).

Answer: Functionally cross-pollination (agent, different flower); genetically self-pollination (same plant).

Example 2: Three outbreeding devices · 3 marks · Short answerBoard level

List three outbreeding devices in flowering plants and explain how each encourages cross-pollination.

Try it first, then show the solutionSolution

Pollen release and stigma receptivity not synchronised: when the flower's own pollen is shed, its stigma is not ready (or the reverse), so it must receive pollen from another flower (1 mark).
Anther and stigma at different positions: self-pollen cannot easily reach the stigma (1 mark).
Self-incompatibility: a genetic mechanism prevents self-pollen from germinating or its tube from growing in the pistil, so only pollen from another plant fertilises the ovules (1 mark).

Answer: Asynchrony of pollen release and stigma receptivity; different positions of anther and stigma; self-incompatibility (also unisexual flowers).

Example 3: Monoecious or dioecious? · 2 marks · Very short answerHarder board level

A farmer grows castor and papaya. In which plant can geitonogamy still occur? Explain why, and state which plant has the stronger guarantee of cross-pollination.

Try it first, then show the solutionSolution

Castor is monoecious: male and female flowers are on the same plant, so autogamy is prevented but pollen can still move between flowers of the same plant (geitonogamy) (1 mark).
Papaya is dioecious: male and female flowers are on different plants, so both autogamy and geitonogamy are prevented; papaya is assured of xenogamy (1 mark).

Answer: Geitonogamy possible in castor (monoecious); papaya (dioecious) can only be cross-pollinated.

Example 4: Reading a flower · 3 marks · Short answerHarder board level

A flower has no petals worth noticing, no scent, long hanging stamens and a large, branched, feathery stigma. Its pollen is dry and powdery. (a) Name the likely agent. (b) Give the purpose of any two features. (c) Why are such plants often seen with many flowers packed in an inflorescence?

Try it first, then show the solutionSolution

(a) Wind (1 mark).
(b) Long exposed stamens release pollen into the air; feathery stigma traps airborne pollen; light, non-sticky pollen is easily carried (any two) (1 mark).
(c) Wind carries pollen at random and most is wasted; many flowers in one inflorescence (with often one ovule per ovary) raise the chance that each ovule receives a grain (1 mark).

Answer: Wind; exposed stamens release pollen, feathery stigma traps it; packed inflorescence increases the chance of capture.

Example 5: Pansy's two kinds of flowers · 3 marks · Short answerHOTS / competency

Viola produces both chasmogamous and cleistogamous flowers. Explain the advantage and the disadvantage of cleistogamous flowers, and why having both is a good strategy.

Try it first, then show the solutionSolution

Advantage: cleistogamous flowers never open, so they are self-pollinated and set seed even when pollinators are absent (assured seed set) (1 mark).
Disadvantage: only self-pollination occurs, so no new genetic combinations are brought in, and continued selfing can cause inbreeding depression (1 mark).
Chasmogamous flowers open and allow cross-pollination when pollinators are around, bringing variation; together the plant gets both assured seeds and variability (1 mark).

Answer: Cleistogamy assures seed set but gives no variation; chasmogamy allows cross-pollination; both together combine security with variability.

Example 6: Water pollination and its exceptions · 3 marks · Short answerHarder board level

Describe pollination in Vallisneria and in seagrasses. Why are water hyacinth and water lily, though aquatic, not water-pollinated?

Try it first, then show the solutionSolution

Vallisneria: female flowers reach the water surface on long stalks; male flowers or pollen are released on the surface and carried passively by water currents to them (1 mark).
Seagrasses (Zostera): female flowers stay submerged; long, ribbon-like pollen grains are carried inside the water; a mucilaginous covering protects pollen from wetting (1 mark).
Water hyacinth and water lily flowers emerge above the water surface, so they are pollinated by insects or wind, as in most land plants (1 mark).

Answer: Vallisneria at the surface, seagrasses below it; water hyacinth and water lily flowers stand above water and use insects or wind.

Where students lose marks in Pollination and Outbreeding Devices

The slips examiners see most often, and what to write instead.

Mistake: Calling geitonogamy cross-pollination without qualification
Students see two flowers and assume cross.
Wrong working
Geitonogamy is cross-pollination as it involves two flowers.
Right working
Geitonogamy is functionally cross but genetically self-pollination.
Do this: Always add the genetic point: same plant, same genes.
Usually costs: 1 mark in 2-mark comparisons.
Mistake: Saying monoecy prevents geitonogamy
Students treat all unisexual flowers alike.
Wrong working
Castor bears unisexual flowers, so both autogamy and geitonogamy are prevented.
Right working
Monoecious (castor, maize): only autogamy prevented. Dioecious (papaya): both prevented.
Do this: Ask whether male and female flowers are on the same plant.
Usually costs: 1 mark.
Mistake: Emasculating after the anthers have opened
Students omit 'before dehiscence'.
Wrong working
Remove the anthers from the flower.
Right working
Remove the anthers from the flower bud before the anthers dehisce.
Do this: Write 'bud' and 'before dehiscence' in every emasculation answer.
Usually costs: ½-1 mark.
Mistake: Listing pollen robbers as pollinators
Any insect on a flower is assumed to pollinate.
Wrong working
All insects visiting flowers bring about pollination.
Right working
Pollen or nectar robbers consume rewards without pollinating.
Do this: A pollinator must touch anthers and then a stigma.
Usually costs: 1-mark MCQ or AR.

Exam tips

Define each kind of pollination by the source of pollen, then give one feature: a 1-mark definition becomes a 2-mark answer.
Name examples precisely: Viola, Oxalis, Commelina (cleistogamous); Vallisneria, Hydrilla, Zostera (water); castor, maize (monoecious); papaya (dioecious).
In outbreeding-device answers, link each device to what it prevents.
For hybridisation, use the words emasculation, bagging and re-bagging; examiners look for them.
Pollen-pistil interaction ends when the pollen tube enters the ovule; describe it as a chemical dialogue.

Practice questions on Pollination and Outbreeding Devices

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
In which plant do both male and female flowers occur on the same plant, so that pollination can be geitonogamous or xenogamous?
(a) Papaya (b) Maize (c) Date palm (d) Vallisneria
Hint
Monoecious plant.
Answer
(b) Maize.
Q2 · 1 mark · MCQBoard level
Arrange in order the steps of artificial hybridisation in a plant with bisexual flowers: (i) re-bagging (ii) selection of parents (iii) bagging (iv) dusting pollen on the stigma (v) emasculation.
(a) ii, v, iii, iv, i (b) ii, iii, v, iv, i (c) v, ii, iii, iv, i (d) ii, v, iv, iii, i
Hint
Emasculate before bagging.
Answer
(a) ii, v, iii, iv, i.
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): The pistil can accept compatible pollen and reject incompatible pollen.
Reason (R): Pollen and pistil interact through an electrical signal that lets only compatible pollen germinate.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
What mediates the dialogue?
Answer
(c). The pollen-pistil dialogue is mediated by chemical components, not an electrical signal.
Q4 · 3 marks · Short answerHOTS / competency
Suppose a researcher finds a plant species in which every flower's stigma becomes receptive several days before its own anthers release pollen, and all flowers on a plant open on the same day. (a) Which kind of pollination is prevented? (b) Can geitonogamy occur? Explain. (c) What is the evolutionary benefit?
Hint
All flowers on a plant are at the same stage at the same time.
Answer
(a) Autogamy is prevented, because when a flower's stigma is receptive its own anthers have not yet shed pollen. (b) No (or hardly): all flowers of the plant are at the same stage together, so no flower on the same plant is shedding pollen while the stigmas are receptive; pollen must come from another plant. (c) It enforces xenogamy, bringing genetic variation and avoiding inbreeding depression.
Q5 · 3 marks · Short answerHarder board level
Explain self-incompatibility. Why is it called a genetic device, and how does it differ from dichogamy in what it achieves?
Hint
Where is the block applied: time, or pollen recognition?
Answer
Self-incompatibility is a genetic mechanism in which the pistil blocks pollen from the same flower, or from other flowers of the same plant, by stopping it from germinating or stopping its tube from growing, so that such pollen cannot fertilise the ovules. It is genetic because the pistil recognises pollen carrying the same genes and rejects it. Dichogamy only separates the timing of pollen release and stigma receptivity; self-incompatibility works even when self-pollen reaches a receptive stigma, so it also blocks geitonogamy.
Q6 · 4 marks · Case-basedHarder board level
Read and answer.
Suppose a student watches four flowers in a botanical garden: Flower W has a huge, foul-smelling bloom about 6 feet tall where beetles lay eggs; Flower X opens at night, is white and strongly fragrant; Flower Y is a grass with dangling anthers; Flower Z is an orchid that resembles a female insect.
(a) Which flower uses wind? (1)
(b) Which kind of animal probably pollinates X, and what tells you so? (1)
(c) Name the reward offered by W and the phenomenon shown by Z. (2)
Hint
Night, pale, fragrant; safe place for eggs; sexual deceit.
Answer
(a) Y, the grass. (b) Moths or bats: night opening, pale colour but strong fragrance. (c) W (as in Amorphophallus) offers a safe place to lay eggs; Z shows pseudocopulation: a male insect mistakes the flower for a female and pollinates it while trying to mate.
Q7 · 2 marks · Very short answerHarder board level
Why is emasculation not required in a plant like papaya during artificial hybridisation? What step is still needed?
Hint
Unisexual flowers.
Answer
Papaya is dioecious; female flowers have no anthers, so there is nothing to remove. The female flower buds must still be bagged before they open to keep out unwanted pollen, then dusted with the chosen pollen and re-bagged.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Which flowers never open?Show answer
Cleistogamous flowers.
2.Name a plant with both chasmogamous and cleistogamous flowers.Show answer
Viola (pansy), Oxalis or Commelina.
3.Which kind of pollination brings genetically different pollen?Show answer
Xenogamy.
4.What are the 'tassels' of a corn cob?Show answer
The stigmas and styles.
5.Why is papaya assured of cross-pollination?Show answer
It is dioecious.
6.What guides the pollen tube into the synergid?Show answer
The filiform apparatus.

Pollination and Outbreeding Devices: frequently asked questions

What are the three types of pollination?

Autogamy (pollen to the same flower), geitonogamy (to another flower of the same plant) and xenogamy (to a flower of a different plant).

What are outbreeding devices?

Features that discourage self-pollination and encourage cross-pollination: non-synchronised pollen release and stigma receptivity, different positions of anther and stigma, self-incompatibility and unisexual flowers.

Why is emasculation done?

To remove the anthers of a bisexual flower bud before they dehisce, so the flower cannot pollinate itself and only the breeder's chosen pollen reaches the stigma.

What is the difference between chasmogamous and cleistogamous flowers?

Chasmogamous flowers open and expose their anthers and stigma; cleistogamous flowers never open and are always self-pollinated.

What is pollen-pistil interaction?

All the events from pollen landing on the stigma to the pollen tube entering the ovule, including the chemical recognition by which the pistil accepts compatible pollen and rejects incompatible pollen.