What is seed germination? Describe the various external and internal factors required for it.

Explanation

Germination as the process by which a plant grows from a seed.
Seed germination is the beginning or resumption of growth by a seed or the process by which the dormant embryo, grows out of the seed-coat and establishes itself as a seedling is called germination.
This is of three types-
1. Epigeal germination
2. Hypogeal germination and
3. Viviparous germination
Seed germination depends on both external and internal factors. The most important external factors include-
(i) Temperature
(ii) Water
(iii) Oxygen or air
(iv) .Light or darkness.
(i) Temperature. It affects cellular metabolic and growth rates. Seeds often have a moderate temperature range of 25-30°C. Some seeds require exposure to cold temperature (vernalisation) to break dormancy e.g., Family Raunculaceae.
(ii) Water. It is required for germination. The hydrolytic enzynes are activated wiitu acids imbibe water, which break down stored food into metabolic useful components, Waler imbibed also causes seed swelling and breaking of seed coat. Water activates the protoplasm of seed cells.
(iii) Air or Oxygen. `O_2` is used for aerobic respiration for energy needs and metabolic activities.
(iv) Light or Darkness. Many seeds are not affected by light, but many will not germinate in the forest until an opening in the canopy allows sufficient light for growth of the seedling.
Internal factors include. (i) Vitality, (ii) viability or longevity, (iii) Dormancy.
(i) Vitality. The ability of a seed to germinate when provided with optimum condition is called as vitality. It depends on its stored food, health, etc.
(ii) Longevity. With passage of time a seed losses its power to germinate. Most of the crop plants loose their viability within 2-5 years. Some seeds remain viable only for one season e.g., Elm, Tea, and some remain viable even after 100 years e.g., Trifolium, Mimosa species.
(iii) Dormancy. It is due to internal conditions of seed which inhibit its germination. These restrictions must be offest in otherwise viable seed, e.g., Tough seed coat, toxins etc.