Define seed germination. Explain its two types and write down the conditions for germination.

Seed germination is the process by which a dormant seed resumes growth and develops into a seedling under favorable conditions. It involves a series of biochemical and physiological changes leading to the emergence of the embryonic root (radicle) and shoot (plumule).

Process of Germination:

1. Imbibition: The seed absorbs water, which activates enzymes and softens the seed coat.

2. Enzyme Activation: The absorbed water triggers enzymes that convert stored food (starch) into energy.

3. Cell Division and Growth: The cells in the embryo divide rapidly, and the seed coat breaks open.

4. Emergence of Radicle and Plumule: The radicle emerges first to form roots, followed by the plumule, which grows into the shoot.

Types of Germination:

1. Epigeal Germination:

The cotyledons (seed leaves) are pushed above the soil due to the elongation of the hypocotyl.

Example: Beans, Castor.

2. Hypogeal Germination:

The cotyledons remain underground, and the plumule emerges above the soil as the epicotyl elongates.

Example: Pea, Maize.

Conditions Required for Germination:

1. Water: Essential for activating enzymes and softening the seed coat.

2. Oxygen: Required for respiration, which provides energy for growth.

3. Temperature: Suitable temperatures (15-30°C) enhance enzymatic activity.

4. Light/Darkness: Some seeds require light (lettuce) or darkness (onion) for germination.