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GERMINATION OF SEEDS
Germination is the stage when embryo develops into a seedling and it also refers to all the changes that occur when the embryo in a seed resumes its growth and development to become an independent seedling.
When the seed is about to germinate, it absorbs several times its own weight of water and swells up.
TYPES OF GERMINATION
There are two types of germination:
Epigeal germination: This is when the hypocotyl grows rapidly and elongates carrying the cotyledon above the soil where they carry out photosynthesis before the first foliage leaves develop.
Epigeal germination is also referred to as a type of germination in which the cotyledon is carried above the soil.
Examples of plants with epigeal germination are castor and cowpea plant
Description of Epigeal Germination
- Seed absorbs/imbibes water and swells.
- Testa splits and the radicle emerges
- The hypocotyls of the germinating seed elongates
- It pushes the seed out of the soil.
- The cotyledon(s) become exposed to the sunlight
- Cotyledons turn green to photosynthesize
- The plumule develops into a green shoot
- The cotyledon(s) dry up/shrink and fall off.
Hypogeal Germination
The epicotyls grow rapidly and elongates, leaving the cotyledons in the soil. Hypogeal germination is the type of germination in which the cotyledons remain in the soil.
Examples of plants with hypogeal germination are maize, gram seed and yam bean.
Differences between Epigeal And Hypogeal Germination
| Epigeal germination | Hypogeal germination |
| 1. Hypocotyl elongates | 2. Epicotyl elongates |
| 2. Cotyledon emerges out of the soil | 2. Cotyledon remains in the soil |
| 3. Cotyledon(s) turns green/photosynthesis | 3. Cotyledons do not photosynthesis |
| 4. Plumule does not emerge simultaneously with the radical | Plumule emerges simultaneously with the radical |
| 5. Food/energy derived from cotyledon | 5. Food/energy derived from endosperm |
CONDITIONS NECESSARY FOR GERMINATION
External conditions are:
- Availability of water,
- Temperature/warmth and
- Availability of oxygen.
Internal conditions are:
- Enzymes
- Energy/food and
- Viability of seed
EXPERIMENT 1: to show the conditions necessary for germination.
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