Seed Germination With Different Types And Causes

Seed Germination: Means the resumption of growth by embryo & development of a young seedling from the seed. Germination is an activation of dormant embryo to give rise to radical (root development) and plumule (stem development).Germination is the awakening of the dormant embryo. The process by which the dormant embryo wakes up & begins to grow is known as Germination.

Seed Emergence Means actually coming above and out of the soil surface by the seedling.

Changes During Germination:
1) Swelling of seed due to imbibition of water by osmosis.
2) Initiation of physiological activities such as respiration & secretion of enzyme.
3) Digestion of stored food by enzymes.
4) Translocation & assimilation of soluble food.
When seed is placed in soil gets favorable conditions, radical grows vigorously & comes out through micro Pyle & fixes seed in the soil. Then either hypo or epicotyls begins to grow.

(Seed Germination)

Types of germination:

1. Hypogeal germination: The cotyledons remain under the soil. E.g.: cereals, gram.

2. Epigeal germination: The cotyledons pushed above the soil surface. E.g.: mustard, tamarind, sunflower, castor, onion.

Seed Dormancy

Seed Dormancy: Failure of fully developed & mature viable seed to germinate under favourable conditions of moisture & temperature is called resting stage or dormancy and the seed is said to be dormant. Kinds of Dormancy in Seeds:

1. Primary dormancy: The seeds which are capable of germination just after ripening even by providing all the favourable conditions are said to have primary dormancy. E.g.: Potato.

2. Secondary dormancy: Some seeds are capable of germination under favourable conditions just after ripening but when these seeds are stored under unfavourable conditions even for few days, they become incapable of germination.

3. Special type of dormancy: Sometimes seeds germinate but the growth of the sprouts is found to be restricted because of a very poor development of roots & coleoptiles.

(Seed Germination)

Causes of Dormancy:

The dormancy in seeds may be due to any single or a combination of more than one of the following causes.

1. Seed coats being impermeable to water: Some seeds have a seed coat which is impermeable to water. Such seeds even when fully matured & placed in favourable conditions; fail to germinate because of failure of water to penetrate into the hard seed coats. These seeds become permeable, if they are treated with H2SO4 or dipped in boiling water for few seconds. E.g.: Cotton.

2. Hard seed coat: Seeds of mustard, amaranths, etc. contain a hard & strong seed coat which prevents any appreciable expansion of embryo. Thus, if the seed coats fail to burst the embryo will remain dormant even after providing all the favourable conditions for germination.

3. Seed coats being impermeable to O: The seed coats are impermeable to O2 & if the seed coats do not rupture the seed fails to sprout.

4. Rudimentary embryo of seeds: The seeds which are apparently ripened contain a rudimentary or imperfectly developed embryo and the germination of such seeds naturally gets delayed until the embryo develops properly.

5. Dormant embryo: The seeds of an apple, peach, pinus, etc. do not germinate even though the embryos are completely developed and all the favourable conditions for germination are provided. In such seeds, physiological changes called after ripening take place during the period of dormancy which enables the seeds for germination.

6. Synthesis & accumulation of germination inhibitors in the seeds: Plant organs synthesize some chemical compounds which are accumulated in the seeds at maturity and these chemicals inhibit the germination of their seeds.

(Seed Germination)