Following double fertilisation, events of endosperm and embryo development, maturation of ovule(s) into seed(s) and ovary into fruit, are collectively termed post-fertilisation events.

1. Post-Fertilisation Events

Definition

The events that occur after fertilisation in a flower are called post-fertilisation events.

These include:

Development of endosperm
Development of embryo
Conversion of ovule into seed
Conversion of ovary into fruit

Double Fertilisation

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Post-Fertilisation Events

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┌────────┼─────────┐

↓ ↓ ↓

Endosperm Embryo Seed & Fruit

2. Endosperm

What is Endosperm?

Endosperm is a nutritive tissue formed inside the seed after fertilisation.

It provides food and nourishment to the developing embryo.

Formation of Endosperm

After triple fusion:

A Primary Endosperm Nucleus (PEN) is formed.
PEN divides repeatedly.
It develops into a triploid (3n) endosperm tissue.

Why Does Endosperm Develop Before Embryo?

Because the embryo needs food for its growth and development.

Therefore: Endosperm develops first and supplies nutrition to the embryo.

Triple Fusion

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Primary Endosperm Nucleus (PEN)

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Repeated Cell Divisions

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Endosperm Tissue

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Food Supply to Embryo

3. Free-Nuclear Endosperm

Definition

When PEN undergoes repeated nuclear divisions without cell wall formation, the endosperm is called Free-Nuclear Endosperm.

Characteristics

✔ Many nuclei are formed.

✔ No cell walls are present initially.

✔ Nuclei remain free in the cytoplasm.

PEN

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Nuclear Divisions

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○ ○ ○ ○ ○ ○ ○

(Free Nuclei)

4. Cellular Endosperm

After the formation of free nuclei:

Cell walls are formed around the nuclei.
The endosperm becomes cellular.

This stage is called Cellular Endosperm.

Free-Nuclear Endosperm

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Cell Wall Formation

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Cellular Endosperm

Important Note

The liquid inside a tender coconut contains thousands of free nuclei and represents the free-nuclear stage of endosperm.

5. Fate of Endosperm

The endosperm may either:

A. Be Completely Consumed

The developing embryo uses all the endosperm before seed maturation.

Examples:

Pea
Groundnut
Bean

Such seeds are called Non-endospermic (Exalbuminous) Seeds.

B. Persist in Mature Seed

Some endosperm remains stored in the mature seed and is used during germination.

Examples:

Castor
Coconut

Such seeds are called Endospermic (Albuminous) Seeds.

Non-Endospermic Seeds	Endospermic Seeds
Pea	Castor
Groundnut	Coconut
Bean	Maize

Term	Meaning
Endosperm	Nutritive tissue of seed
PEN	Primary Endosperm Nucleus
Free-Nuclear Endosperm	Endosperm with free nuclei and no cell walls
Cellular Endosperm	Endosperm with cell walls
Albuminous Seed	Seed with persistent endosperm
Exalbuminous Seed	Seed without endosperm at maturity

Check Your Progress

1. The events occurring after fertilisation are collectively known as:

A. Pollination events
B. Pre-fertilisation events
C. Post-fertilisation events
D. Germination events

2. Which tissue provides nourishment to the developing embryo?
A. Ovule
B. Endosperm
C. Cotyledon
D. Ovary

3. The Primary Endosperm Nucleus (PEN) is:
A. Haploid (n)
B. Diploid (2n)
C. Triploid (3n)
D. Tetraploid (4n)

4. Why does endosperm develop before the embryo?
A. To form fruit
B. To produce pollen
C. To provide nutrition to the embryo
D. To protect the ovule

5. The stage of endosperm development in which nuclei divide without cell wall formation is called:
A. Cellular endosperm
B. Free-nuclear endosperm
C. Albuminous endosperm
D. Embryonic endosperm

6. Coconut water represents:
A. Embryo
B. Cellular endosperm
C. Free-nuclear endosperm
D. Cotyledon

7. The white kernel of coconut is an example of:
A. Free-nuclear endosperm
B. Cellular endosperm
C. Embryo
D. Pericarp

8. Which of the following seeds is non-endospermic at maturity?
A. Coconut
B. Castor
C. Pea
D. Maize

9. Endosperm persists in mature seeds of:
A. Pea and Bean
B. Groundnut and Pea
C. Castor and Coconut
D. Bean and Groundnut

10. The ovary develops into a ______ after fertilisation.

A. Seed
B. Fruit
C. Embryo
D. Endosperm