EXPERIMENT 10

PLANT GROWTH AND DEVELOPMENT: Seed Germination

A seed is a plant embryo which contains within itself virtually all the materials and energy

to start a new plant. Germination of seeds is the resumption of growth. It is a process governed

by environmental factors (such as light, availability of water, soil temperature, and oxygen

levels) and genes. This complex physiological process is triggered by the imbibition or the

uptake of water.

Seeds have three major parts: dormant embryo, storage tissue, and the seed coat. The

Dormant Embryo is the essential living part of the seed which consists of a radicle (gives rise

to the root), and a plumule (gives rise to young shoot). The part containing these two is called

the hypocotyl. Storage Tissue is the reserve of food which supplies the embryo and the

growing plant until it is able to make its own food. The storage tissue may be in the cotyledons

or in a part of the seed called the endosperm. Seed Coat, also known as testa, is the tough

protective outer covering of the seed. It often has outgrowths which help in the dispersal of the

seed.

The specimen under study is Corn Grain/Seed (Zea mays), a representative of the

monocots (having only one cotyledon/seed leaf) and of the endospermous/ albuminous seeds

(having endosperm as the storage tissue).

OBJECTIVES:

The experiment concerns with the analysis of the germination process of Zea mays.

Specifically, the study aims to:

• Determine the different plant organs of a germinating corn grain (Zea mays).

• Establish the phasic changes that the corn grain (Zea mays) undergoes in the process of

germination

MATERIALS

• corn grains (Zea mays)

• 1% clorox

• Rectangular pan with cover

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METHODOLOGY

The corn grains were first rinsed with 1% Clorox, and then were allowed to germinate

along the side of the pan. For the succeeding days, stages of germination depicting

morphological changes were identified.

RESULTS AND DISCUSSIONS:

During germination process, primary root first emerges through seed coat. It is then

followed by hypocotyl emergence. As it grows up, it takes the shape of hairpin, known as

hypocotyl arch.

The external parts of the corn grain (monocot) are the pedicel, embryo, seed coat and the

pericarp.

• The pedicel is the floral unit.

• The embryo is the part that develops into a new plant.

• The seed coat protects the embryo from injury and prevents it from drying.

• The pericarp is the part that encloses the seed.

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External

Structures of Corn

grains (Zea mays)

Embryo

seed coat + pericarp

Pedicel or flower stalk

GUIDE QUESTIONS

Q: What is the term for water intake by a germinating seed?

A: The process is called IMBIBITION. It initiates germination of the seed by the uptake of water.

Imbibition causes a swelling of the seed which generates substantial pressure (imbibition

pressure) which will further lead to the rupture of the testa, thus permitting the embryo to

emerge.

Q: Which part of the embryo emerged first during seed germination?

A: Radicle (embryonic root) first emerges from the seed coat. Radicle emergence occurs

through a combination of cell enlargement within the radicle itself and imbibition pressures

developed within the seed. This mechanism is advantageous since it allows the plant to make

contact with water and nutrient salts required to support further growth of the young seedling.

CONCLUSION

Seed germination begins with the imbibition of water to hydrate the relatively dry seed

tissues. This is followed by radicle emergence and elongation of the shoot which leads to the

establishment of a young seedling.

The driving force for germination is therefore the turgor changes that are due to the

imbibition pressures within the seed tissues.

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