Types Of Germination, Process And Conditions

Hi, welcome to this hall on the types of germination, the process and conditions that are necessary of germination.

Table Of Contents

1. Germination of seeds
2. Definition of germination
3. Types of germination
4. Process of germination
5. Conditions necessary for germination
6. Revision Questions

Definition Of Germination

Germination is defined as the process which involves the gradual development of the embryo of a seed into a seedling or a young plant. In other words, germination is the series of Changes by which an embryo in a seed grows into seedlings.

The embryo of developed seeds usually passed through a period, there is very little cell activity. The seeds can remain in this condition as long as they are dry and the condition for germination is not favorable. When conditions become favorable, the seeds undergo several changes to develop into seedlings.

Types Of Germination

There are two types of germination. These are epigal germination and hypogeal germination.

Epigeal Germination

Definition: Epigeal germination is defined as the types of germination in which cotyledons or seed leaves are carried above the soil surface. Epigeal germination is associated with dicotyledonous plants, e.g. germination of cowpea, groundnut, melon and mango.

Hypogeal Germination

Definition: Hypogeal germination is defined as a types of germination in which the cotyledons, seed leaves or endosperm remain below the soil surface. Hypogeal germination is associated with monocotyledonous plants, e.g. germination of maize, oil palm, Guinea corn, millet and wheat.

Differences between epigeal germination and hypogeal germination

Epigeal germination – Hypogeal germination

1. Testa splits – Pericarp splits
2. Hypocotyle emerges uncovered – hypocotyle covered by sheat/coleorrhiza.
3. Cotyledons are carried above the soil – cotyledons remains in the soil.
4. Energy obtained from food is stored in the cotyledon – energy obtained from food is stored in the endosperm.
5. Hypocotyle elongate – epicotyle elongate.
6. Cotyledon is the first photosynthetic tissue – foilage leaves are the first photosynthetic tissue.

Process Of Germination

(A) germination in cowpea: Cowpea exhibits epigeal germination i.e. during germination, the cotyledon (seeds leaves) are carried above the soil. When the seed is placed in the soil,

• it absorbed water and swells up.
• the testa of seed coat splits
• the radicle appears and grows downward into the soil,
• the plumule (seed leaves) appears and grows upward above the soil.

As the seedlings grows, the food stored in the cotyledon is used up and the seed leaves eventually dries up and wither off. As the seed absorbs water, enzymes become active and the rate of respiration will increase and the sibling growth is speeded up.

(B) germination in maize: Maize grain exhibits hypogeal germination, i.e. during germination, the cotyledon (seed leaves or endosperm) remains under the soil. When maize seed is placed in the soil,

• it absorbs water and swells up,
• the testa or seed coat splits,
• the radicle appears and grows downward into the soil,
• the seed leaf (endosperm) remains below the soil,
• the plumule (ordinary leaves) appear and grow upwards above the soil.

As the seedlings grows, the food stored in the endosperm below the soil is used up and it eventually withers off. The seed absorbs water, the enzymes become active, rate of respiration increases and the seedlings growth rate is increased.

Conditions Necessary For Germination

The conditions which are necessary for the germination of seed include:

1. Water or moisture
2. Air or oxygen
3. Warmth or suitable temperature
4. Enzymes
5. Energy or food
6. Viable seeds.

1. Water or moisture: The seed needs water to activate the cell. It is also needed to soften the testa or seed coat so that the radical and plumule can come out of the seed with ease.

2. Air or oxygen: The seed is a living organ. It needs oxygen to carry out respiration. During respiration, energy is released and it is used by the seed to grow

3. Warmth or suitable temperature: Some seeds requires certain range of temperature to germinate. This range in temperature is called optimum temperature. Below or above this temperature, the seed may or will not germinate and may even die.

4. Enzymes: Enzymes are organic catalyst which speed up the rate of reaction with the cells in the seed. Enzymes are required in the breaking down of food to release energy.

5. Energy or food: There must be food within the seed from which it feeds. In dicotyledonous seed, the food is stored in the cotyledons or seed leaves while in a monocotyledonous seed, the food or energy source is stored in the endosperm.

6. Viable seeds: For a seed to germinate, it must be viable or alive. Damaged in seeds by insects, birds or man cannot germinate hence such seeds are not viable.

Revision Questions

1. (a) what is germination? (b) explain the types of germination of seeds (c) enumerate and explain the conditions that are necessary for germination to take place.
2. Describe the process of germination in a maize seed.