Sexual Reproduction in Flowering Plants — Part 2: Pollination: visual lesson, CBSE Class 12 Biology

Lesson

Pollination

Part 2 — how pollen, which cannot move by itself, reaches a stigma, and how plants encourage cross-pollination.

In this lesson you will

Distinguish autogamy, geitonogamy and xenogamy, and chasmogamous and cleistogamous flowers
Relate floral features to wind, water and animal pollination
Explain outbreeding devices and pollen–pistil interaction
Describe emasculation and bagging in artificial hybridisation

Diagram

Three kinds of pollination

Autogamy: pollen reaches the stigma of the same flower. Geitonogamy: pollen reaches another flower of the same plant. Xenogamy: pollen reaches a flower of a different plant.

Concept

Open and closed flowers

For autogamy, anther dehiscence and stigma receptivity must coincide, and anther and stigma must be close. Some plants, such as Viola (common pansy), Oxalis and Commelina, make two kinds of flowers.

Table comparing chasmogamous and cleistogamous flowers
	Chasmogamous flowers	Cleistogamous flowers
Opening	Open, anthers and stigma exposed	Never open
Pollination	Self or cross	Only autogamy
Pollinator needed	Usually	No
Seed set	Depends on pollinators	Assured, even without pollinators
Variation	Possible	Very little

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