BiologyISC Class 12 · Sexual Reproduction in Flowering Plants

Pollination and Outbreeding Devices: ISC Class 12 Notes and Questions

Updated 15 October 2026 · Fact-checked

Pollination is the transfer of pollen from an anther to a stigma. ISC classifies it as autogamy, geitonogamy or xenogamy, with chasmogamous and cleistogamous flowers. Contrivances that prevent self-pollination are unisexuality, dichogamy, herkogamy and self-incompatibility. Breeders control pollination by emasculation and bagging.

Understand Pollination and Outbreeding Devices

Why pollination is needed. In flowering plants both gametes are non-motile: the male gametes are inside the pollen grain and the egg is deep inside the ovule. Some outside agent must carry pollen to the stigma before fertilisation can follow. ISC asks you to classify pollination, link floral adaptations to agents, list contrivances against selfing, explain pollen-pistil interaction and describe artificial hybridisation.

Kinds of pollination (by the source of pollen).

Autogamy: pollen reaches the stigma of the *same flower*. In an open flower this needs anthers and stigma to mature together and to lie close.
Chasmogamy is the condition of flowers that open and expose anthers and stigma; such flowers can be self- or cross-pollinated. Cleistogamy is the condition of flowers that never open; pollen from anthers dehiscing inside the closed bud reaches the stigma, so cleistogamous flowers are always autogamous and set seed even without pollinators. Viola (pansy), Oxalis and Commelina bear both types.
Geitonogamy: pollen reaches another flower of the *same plant*. Ecologically (functionally) it is cross-pollination, because an agent must carry pollen between two flowers; genetically it is self-pollination, because both flowers have the same genotype.
Xenogamy: pollen reaches a flower of a *different plant of the same species*. It is the only kind that brings genetically different pollen.

Self- versus cross-pollination. Self-pollination is sure, needs no agent, wastes little pollen and keeps a pure line pure, but repeated selfing reduces vigour (inbreeding depression) and gives no new combinations. Cross-pollination brings variation, vigour and better adaptability, but depends on agents and wastes much pollen.

Agents and floral adaptations.

Wind (anemophily): commonest abiotic mode, frequent in grasses. Pollen light, dry, non-sticky and produced in huge numbers; stamens well exposed; stigma large and often feathery; often one ovule per ovary and many flowers in an inflorescence. In maize the silky threads of the cob are the styles and stigmas.
Water (hydrophily): rare, about 30 genera, mostly monocots. In Vallisneria the female flower reaches the surface on a long stalk and male flowers or pollen drift on the surface to it; in seagrasses such as Zostera the female flowers stay submerged and long ribbon-like pollen is carried inside the water. A mucilaginous coat keeps pollen from wetting. Most aquatic plants (water hyacinth, water lily) hold flowers above water and use insects or wind.
Wind- and water-pollinated flowers are usually dull and nectarless: they need not attract anyone.
Insects (entomophily) and other animals: flowers large, colourful, scented and nectar-rich; small flowers are massed into an inflorescence; pollen is sticky. Fly and beetle flowers smell foul. Rewards are nectar, pollen or a safe egg-laying site (Amorphophallus; the yucca plant and its moth depend on each other). Visitors that take rewards without touching anther and stigma are pollen or nectar robbers.

Contrivances for prevention of self-pollination (outbreeding devices). ISC expects each one *named* and then explained.
1. Unisexuality (dicliny): monoecious plants (castor, maize) bear male and female flowers on one plant, preventing autogamy but not geitonogamy; dioecious plants (papaya, date palm) bear them on separate plants, preventing both.
2. Dichogamy: anthers and stigma of a bisexual flower mature at different times. Protandry: anthers first (sunflower). Protogyny: stigma first (Mirabilis).
3. Herkogamy: a physical barrier or a difference in position keeps self-pollen off the stigma. Heterostyly is a special case: flowers of different plants have styles and stamens of different lengths (Primula), so pollen is carried effectively only between the two forms.
4. Self-incompatibility (self-sterility): a genetic mechanism; pollen from the same flower or the same plant falls on a receptive stigma but cannot germinate, or its tube stops in the style.

Dichogamy and herkogamy prevent autogamy; self-incompatibility and dioecy prevent geitonogamy as well.

Pollen-pistil interaction. The pistil recognises pollen as compatible (right species, not self in a self-incompatible plant) or incompatible through a dialogue between chemical components of pollen and pistil. Compatible pollen germinates through a germ pore; the tube grows through stigma and style, reaches the ovary, enters the ovule through the micropyle and then a synergid, guided by the filiform apparatus. Incompatible pollen is stopped at germination or tube growth. Pollen of an unrelated species (China-rose pollen on a rose stigma) is rejected in this way.

Flow chart: pollen on stigma → recognition → germination → tube through style → ovary → micropyle → synergid (filiform apparatus) → two male gametes released.

Artificial hybridisation. Used to combine desirable characters of two parents. (1) Select parents. (2) Emasculation: remove anthers from a bisexual flower *bud* of the female parent before they dehisce. (3) Bagging: cover it with a butter-paper bag. (4) When the stigma is receptive, dust pollen from the male parent. (5) Re-bag until fruit sets. If the female parent bears unisexual flowers, only bagging of female buds is needed.

Draw and label: geitonogamy and xenogamy. Checklist: two plants of one species; plant A with two flowers, plant B with one; an insect arrow from flower 1 to flower 2 of A labelled geitonogamy; an arrow from A to B labelled xenogamy; a curved arrow inside one flower labelled autogamy; labels: anther, stigma, pollinating agent.

Pollination and Outbreeding Devices: key facts

Kinds of pollination: $autogamy (same flower) ∣ geitonogamy (same plant) ∣ xenogamy (another plant)$; Only xenogamy brings new genes; geitonogamy is ecologically cross, genetically self.
What each contrivance prevents: $dichogamy, herkogamy, monoecy \to autogamy; self-incompatibility, dioecy \to autogamy + geitonogamy$; Name the device first, then what it blocks.
Dichogamy: $protandry (anthers first, sunflower) ∣ protogyny (stigma first, Mirabilis)$; A time barrier inside a bisexual flower.
Artificial hybridisation: $select \to emasculate (bud) \to bag \to dust pollen \to re-bag$; Unisexual female flower: skip emasculation.

How to answer Pollination and Outbreeding Devices questions

ISC questions here are case-based (a gardener, a breeder, a flower described), contrivance lists, and 'why is geitonogamy both...' explanations. Use the same routine.

1Find the source of pollen: same flower, same plant or another plant. Name the kind of pollination in the first line.
2If two different species are involved, the answer turns on pollen-pistil interaction: the pistil recognises the pollen as incompatible and blocks germination or tube growth.
3For a contrivance, write the technical name (dichogamy, herkogamy, heterostyly, self-incompatibility, unisexuality), one line of explanation and an example.
4For geitonogamy, give both halves: ecological (needs an agent) and genetic (same genotype).
5For floral adaptations, match each feature to the agent and say what it achieves (catches, carries, attracts or protects pollen).
6For breeding questions, check the flower: bisexual needs emasculation then bagging; unisexual needs bagging only. Write 'before dehiscence'.

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.

Self-incompatibility and planting for cross-pollination

Suppose a farmer plants a large orchard with grafted copies of a single apple tree, all genetically identical, and the variety is self-incompatible. The trees flower heavily and bees visit them, but very little fruit sets.

Explain why fruit set is poor although bees are active, and suggest a remedy.

Try it first, then show the solutionSolution

All the grafted trees share one genotype, so for pollination purposes the whole orchard behaves like one plant.
Bee-carried pollen moving between these trees is therefore 'self' pollen; the pistil recognises it and stops germination or tube growth (self-incompatibility).
Without fertilisation the ovules do not form seeds, and the fruits drop or fail to set.
Remedy: plant rows of a different, compatible variety that flowers at the same time, so bees bring genetically different pollen (xenogamy).

Answer: Pollen moving between genetically identical trees is self pollen and is rejected by self-incompatibility; inter-planting a compatible pollinator variety restores fruit set.

Memory hook: Same genes, same 'self': a clone orchard is one plant to its own pistils.

Tricks to remember Pollination and Outbreeding Devices

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

U-D-H-S: four walls against selfing
Unisexuality, Dichogamy, Herkogamy, Self-incompatibility. 'U Don't Hug Self.'
Use it when: Listing three or four contrivances in a 5-mark answer.
Andro first, gyno first
Prot-ANDR-y: the male (andro) part is first. Prot-OGYN-y: the female (gyno) part is first.
Use it when: Avoiding the protandry/protogyny swap.
Geitono = neighbour
Geiton means neighbour: a neighbour flower on the same plant. Travels like cross, inherits like self.
Use it when: The two-context geitonogamy question.

Pollination and Outbreeding Devices: solved examples

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

Example 1: Chasmogamy and cleistogamy · 2 marks · Short answerBoard level

Distinguish between chasmogamous and cleistogamous flowers. Can a cleistogamous flower ever be cross-pollinated? Give a reason.

Try it first, then show the solutionSolution

Chasmogamous flowers open and expose their anthers and stigma; cleistogamous flowers remain closed throughout (1 mark).
No: anthers dehisce inside the closed flower and no outside pollen can reach the stigma, so cleistogamous flowers are always autogamous (1 mark).

Answer: Chasmogamous open, cleistogamous never open; cleistogamous flowers are invariably self-pollinated.

Example 2: Bisexual yet outbred · 3 marks · Short answerBoard level

A plant bears only bisexual flowers, yet almost all of its seeds come from cross-pollination. Suggest three different features of the plant that could explain this, naming each feature and giving one example where possible. (ISC asked for three such contrivances in 2025.)

Try it first, then show the solutionSolution

Dichogamy: anthers and stigma mature at different times, e.g. protandry in sunflower, protogyny in Mirabilis (1 mark).
Herkogamy: anther and stigma are placed so that self-pollen cannot reach the stigma; heterostyly (Primula) is one form (1 mark).
Self-incompatibility: a genetic mechanism prevents self-pollen from germinating on the stigma or growing through the style (1 mark).

Answer: Dichogamy, herkogamy (heterostyly), self-incompatibility, each named and explained.

Example 3: Rose stigma, marigold pollen · 3 marks · Case-basedHarder board level

Suppose a gardener dusts pollen of marigold on the stigmas of her garden rose flowers, hoping for a new hybrid rose. (a) Will seeds of a hybrid form? Explain. (b) What should she do instead to obtain a hybrid between two rose varieties? (A situation of this kind, with China-rose pollen, was asked in 2024.)

Try it first, then show the solutionSolution

(a) No. Marigold and rose are different species (different families); the rose pistil recognises the foreign pollen as incompatible through pollen-pistil interaction and blocks its germination or tube growth, so no fertilisation occurs (1½ marks).
(b) Choose two rose varieties; emasculate buds of the female parent before the anthers dehisce, bag them, dust pollen of the other rose variety when the stigma is receptive, and re-bag (1½ marks).

Answer: (a) No: interspecific pollen is incompatible and rejected by the pistil. (b) Cross two rose varieties using emasculation, bagging and re-bagging.

Example 4: Geitonogamy in two contexts · 3 marks · Short answerHarder board level

A bee carries pollen from one flower of a mustard plant to another flower on the same plant. Name this kind of pollination, and explain in what sense it resembles cross-pollination and in what sense it is really self-pollination.

Try it first, then show the solutionSolution

Geitonogamy: transfer of pollen from the anther of one flower to the stigma of another flower on the same plant (1 mark).
Ecological: like cross-pollination, it needs a biotic or abiotic pollinating agent to carry pollen between two separate flowers (1 mark).
Genetic: both flowers arise on the same plant and have the same genotype, so the offspring are as if selfed; no new genes are brought (1 mark).

Answer: Pollen to another flower of the same plant: agent-dependent like cross, genetically identical like self.

Example 5: Which device stops geitonogamy? · 4 marks · Short answerHarder board level

A plant breeder lists four plants: (i) sunflower (protandrous), (ii) maize (monoecious), (iii) papaya (dioecious), (iv) a self-incompatible tobacco. In which can geitonogamy result in seed formation? Justify each.

Try it first, then show the solutionSolution

(i) Sunflower: yes. Protandry stops a flower pollinating itself, but in a head the florets open at different times, so pollen of one floret can reach a receptive stigma of another floret on the same plant (1 mark).
(ii) Maize: yes. Monoecy prevents autogamy only; tassel pollen can fall on the silks of the same plant (1 mark).
(iii) Papaya: no. Male and female flowers are on different plants, so there is no second flower of the same plant to pollinate (1 mark).
(iv) Tobacco: no seed. Pollen from the same plant reaches the stigma but self-incompatibility blocks germination or tube growth (1 mark).

Answer: Geitonogamy can give seed in sunflower and maize; it is impossible in papaya and ineffective in self-incompatible tobacco.

Example 6: Hybrid seed every year · 4 marks · Case-basedHOTS / competency

Suppose a seed company produces hybrid tomato seed by hand. Tomato flowers are bisexual and largely self-pollinating. (a) Why is emasculation essential here but bagging alone would be enough for a cucumber crop with unisexual flowers? (b) Why must the bag be put on immediately after emasculation and again after dusting? (c) Suggest one natural floral feature that, if bred into the female line, would save the cost of emasculation.

Try it first, then show the solutionSolution

(a) In a bisexual tomato flower the female parent's own anthers would self-pollinate the stigma; removing them in the bud stage prevents selfing. Cucumber female flowers have no anthers, so only foreign pollen needs to be kept out (1 mark).
(b) The first bagging protects the receptive stigma from stray pollen carried by wind or insects; re-bagging after dusting keeps the chosen pollen as the only pollen on the stigma until fertilisation (1 mark).
(c) Male sterility or self-incompatibility in the female line: its own pollen cannot fertilise it (1 mark); alternatively a strongly protogynous flower, dusted before its anthers open (1 mark).

Answer: (a) Bisexual flowers self-pollinate; unisexual female flowers do not. (b) To exclude unwanted pollen before and after dusting. (c) Self-incompatibility, male sterility or strong protogyny in the female parent.

Where students lose marks in Pollination and Outbreeding Devices

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

Mistake: Writing emasculation and bagging when asked for contrivances
In 2025 examiners reported that many candidates described emasculation and bagging, which are a breeder's techniques, not natural contrivances of the flower.
Wrong working
Contrivances against self-pollination: emasculation, bagging, re-bagging.
Right working
Contrivances: unisexuality, dichogamy, herkogamy, self-incompatibility.
Do this: Contrivances are features of the plant itself; hybridisation steps are human interventions.
Usually costs: The whole part, up to 3 marks.
Mistake: Describing a contrivance without naming it
Examiners (2025) noted answers such as 'anther matures before stigma' with no term.
Wrong working
Anthers mature before the stigma.
Right working
Dichogamy (protandry): anthers mature before the stigma of the same flower.
Do this: Write the technical term first, then the explanation and an example.
Usually costs: ½ mark per contrivance.
Mistake: Missing 'incompatible' in interspecific pollination
In the 2024 rose and China-rose case many candidates said 'yes' and described hybridisation, or did not see that the two plants are different species.
Do this: When pollen and pistil belong to different species, write: incompatible, rejected through pollen-pistil interaction, no fertilisation.
Usually costs: 1 to 2 marks.
Mistake: Half an answer on geitonogamy
Examiners (2024) found candidates did not say the flowers are on the same plant, or left out the pollinating agent for the ecological context.
Do this: Write both: needs an agent (ecological, like cross) and same plant, same genotype (genetic, like self).
Usually costs: 1 mark.

Exam tips

Use the words chasmogamy, cleistogamy, autogamy, geitonogamy and xenogamy exactly; ISC lists them in the syllabus.
For contrivances, give the term, its meaning and an example: protandry (sunflower), protogyny (Mirabilis), heterostyly (Primula), dioecy (papaya).
Link each device to what it blocks: autogamy only, or autogamy and geitonogamy.
In emasculation, write 'flower bud' and 'before the anthers dehisce'.
Pollen-pistil interaction is a chemical recognition between pollen and pistil, ending when the tube enters the ovule.

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
Which of the following prevents both autogamy and geitonogamy?
(a) Protandry (b) Monoecy (c) Dioecy (d) Herkogamy
Hint
Male and female flowers on separate plants.
Answer
(c) Dioecy.
Q2 · 2 marks · Short answerBoard level
Give two features each of wind-pollinated and insect-pollinated flowers.
Hint
Think about what each flower must achieve: catch pollen or attract an animal.
Answer
Wind: light, dry, non-sticky pollen in large amounts; exposed stamens; large feathery stigma (any two). Insect: large, bright, scented petals; nectar; sticky pollen (any two).
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Cleistogamous flowers give assured seed set.
Reason (R): Cleistogamous flowers depend on insects to bring pollen from other plants.
(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
Do cleistogamous flowers open?
Answer
(c). They never open and are self-pollinated without any agent, which is why seed set is assured.
Q4 · 2 marks · Short answerHarder board level
Differentiate between protandry and protogyny with one example each, and state which kind of pollination both prevent.
Hint
Which part matures first?
Answer
Protandry: anthers mature and shed pollen before the stigma of the same flower is receptive (sunflower). Protogyny: the stigma is receptive before the anthers of that flower open (Mirabilis). Both are forms of dichogamy and prevent autogamy.
Q5 · 2 marks · Short answerHarder board level
Explain why Vallisneria and seagrasses, though both water-pollinated, differ in where pollination takes place, and name the feature that protects their pollen.
Hint
Surface versus submerged.
Answer
In Vallisneria the female flower is raised to the water surface on a long stalk, and male flowers or pollen float on the surface to it. In seagrasses (Zostera) the female flowers stay under water and long ribbon-like pollen is carried inside the water. In both, a mucilaginous covering protects the pollen from wetting.
Q6 · 3 marks · Short answerHarder board level
State two advantages and one disadvantage of self-pollination, and two advantages of cross-pollination.
Hint
Certainty versus variation.
Answer
Self-pollination: sure even without agents; little pollen is wasted; parental characters (pure lines) are kept (any two). Disadvantage: repeated selfing causes inbreeding depression and no new variation. Cross-pollination: brings variation and new gene combinations; offspring are more vigorous and adaptable.
Q7 · 3 marks · Short answerHOTS / competency
Suppose a botanist finds a hermaphrodite flower in which the stigma projects well above the anthers, the flower is protogynous, and yet the plant sets plenty of seed when bagged as a whole plant (all its flowers enclosed together in one large net). (a) Which kind of pollination must be producing the seed? (b) Is the plant self-incompatible? Explain. (c) Which single contrivance, if present, would have stopped this seed set?
Hint
Only pollen from the same plant can reach the stigmas inside the net.
Answer
(a) Geitonogamy (pollen moving between flowers of the same plant inside the net), possibly some autogamy. (b) No: it sets seed with its own pollen, so self-pollen is compatible. (c) Self-incompatibility (or dioecy, which is not possible here as the flower is bisexual); herkogamy and protogyny only block pollen within one flower.
Q8 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose a student watches three plants for a week. Plant P has huge numbers of small flowers in hanging spikes, no scent and dusty pollen. Plant Q has a large white flower that opens at dusk and smells strongly. Plant R has small yellow flowers, some of which never open but still form pods.
(a) Name the likely pollinating agent of P and Q. (1)
(b) What term describes R's closed flowers, and what kind of pollination occurs in them? (1)
(c) Why would R gain from also bearing open flowers? (1)
Hint
Night, white, fragrant; flowers that never open.
Answer
(a) P: wind; Q: night-flying animals such as moths or bats (pale but fragrant, opens at dusk). (b) Cleistogamous; autogamy. (c) Open (chasmogamous) flowers allow cross-pollination and new gene combinations, while closed flowers guarantee some seed.

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.What is xenogamy?Show answer
Transfer of pollen to the stigma of a flower on a different plant of the same species.
2.Name a plant with both chasmogamous and cleistogamous flowers.Show answer
Viola (pansy), Oxalis or Commelina.
3.What is protogyny?Show answer
The stigma becomes receptive before the anthers of the same flower shed pollen.
4.Which condition prevents autogamy but not geitonogamy?Show answer
Monoecy (castor, maize).
5.What covers water-borne pollen?Show answer
A mucilaginous covering that prevents wetting.
6.What is the bag in artificial hybridisation usually made of?Show answer
Butter paper.

Pollination and Outbreeding Devices: frequently asked questions

What are the contrivances for prevention of self-pollination in ISC Biology?

Unisexuality (monoecy and dioecy), dichogamy (protandry and protogyny), herkogamy (including heterostyly) and self-incompatibility.

Why is geitonogamy called functionally cross but genetically self-pollination?

It needs an agent to carry pollen between two flowers, like cross-pollination, but both flowers are on the same plant and share a genotype, so genetically it equals selfing.

What is the difference between dichogamy and herkogamy?

Dichogamy separates anther and stigma in time (they mature at different times); herkogamy separates them in space or by a barrier.

Why is emasculation not needed in unisexual flowers?

A female flower has no anthers, so it cannot pollinate itself; the bud is only bagged to keep out unwanted pollen.

Why does pollen of one species usually fail on the stigma of another?

The pistil recognises it as incompatible through chemical interaction and stops its germination or pollen tube growth.