What is germination? The types of germination and stages of germinations
Germination is the process by which a seed grows into a new plant. It is the awakening of a dormant seed and the initiation of the growth process.
There are two types of germination:
1. Epigeal Germination: In this type of germination, the cotyledons (embryonic seed leaves) emerge above the soil surface during germination. The epicotyl elongates and pulls the cotyledons, which turn green and participate in photosynthesis. Examples of plants undergoing epigeal germination include beans, peas, and sunflowers.
2. Hypogeal Germination: Here, the cotyledons remain underground, and the epicotyl elongates to bring the plumule (embryonic shoot) and the first true leaves above the soil surface. The cotyledons do not participate in photosynthesis. Examples of plants with hypogeal germination include peanuts, maize (corn), and onions.
The stages of germination are as follows:
1. Seed Imbibition: The process begins with the absorption of water by the seed. It causes the seed coat to swell and triggers metabolic activities within the seed.
2. Activation of Enzymes: The absorbed water activates enzymes within the seed that break down stored food reserves, such as starch, proteins, and lipids, into simpler molecules that can be utilized by the developing plant.
3. Radicle Formation: The radicle, the embryonic root, emerges first from the seed and begins to elongate. It anchors the young plant into the soil and aids in the absorption of water and nutrients.
4. Shoot Growth: The epicotyl, which contains the plumule, grows upward and eventually breaks through the soil surface. The plumule develops into the shoot system, giving rise to the stems, leaves, and eventually flowers or cones.
5. Seedling Establishment: As the shoot grows, it begins to produce its own food through photosynthesis, reducing reliance on the stored reserves in the seed. The roots continue to develop and branch out, facilitating water and nutrient uptake from the soil.
These stages are approximate and may vary depending on the plant species, environmental conditions, and other factors.
Germination is the process by which a seed or spore begins to grow and develop into a new plant. It involves the activation of a dormant embryo within the seed, leading to the emergence of the radicle (embryonic root) and the growth of a seedling. There are three main types of germination: epigeal germination, hypogeal germination, and vivipary.
1. Epigeal Germination: In this type of germination, the cotyledons (seed leaves) are pushed above the soil surface. The epicotyl (embryonic shoot) elongates, and the cotyledons expand and become green. Examples include beans, sunflowers, and tomatoes.
2. Hypogeal Germination: Here, the cotyledons remain below the soil surface throughout germination. The epicotyl grows upwards, and the primary leaf emerges after the cotyledons. Examples include peas, corn, and peanuts.
3. Vivipary: This type occurs in certain plants where the embryo starts growing while the seed is still attached to the parent plant. The seedling may emerge directly from the fruit or the seed coat, and roots are often observed. Examples include mangroves, some orchids, and mangroves.
The stages of germination can be summarized as follows:
1. Imbibition: The seed absorbs water, causing it to swell and become activated.
2. Activation: Enzymes and hormones within the seed are stimulated by imbibition, initiating metabolic processes.
3. Germination: The radicle, or embryonic root, emerges from the seed, followed by the growth of the shoot or plumule.
4. Seedling Growth: The seedling continues to grow, producing new leaves, stems, and roots.
5. Photosynthesis: Once the seedling has leaves, it can start performing photosynthesis to produce its own food.
6. Establishment: The seedling becomes firmly rooted in the ground and undergoes further growth and development to mature into a fully functional plant.
It's important to note that the exact stages and processes of germination may vary depending on the plant species.