When the growth of seed starts, it is known as germination. There are two kinds of germination including hypogeal germination and Epigeal germination. Hypogeal germination is the kind of germination in which the seed leaves or the cotyledons do not come out of the surface of earth and remain below the surface of earth. For example, pea seed follows hypogeal germination. Second type of germination is Epigeal germination in which the seed leaves come out of the surface of earth and remain on new shoot. For example Ash tree shows such kind of germination.
There are two types of germination present. A hypogeal germination is where the cotyledons remain below the surface of the soil (e.g. maize and broad bean). The other type of germination is called epigeal germination, where the cotyledons are carried above the ground (e.g. sword bean seed). Maize grain germination can be termed as hypogeal germination.
First of all the radicle emerges, rupturing the radicle sheath or coleorhiza and piercing through the testa and pericarp. It grows downwards and develops a tuft of root hairs just behind its tip. Adventitious roots grow from the base of the stem. This produces a fibrous root system, characteristic of most monocotyledonous plants.
Meanwhile the plumule sheath or coleoptile lengthens. It pierces through the walls of the grain, and grows upwards above the ground. The plumule, which is enclosed and protected by the coleoptile, grows and breaks through the coleoptile. The first foliage leaves appear and unroll. During the whole period the cotyledon remains below the ground. It digests and absorbs the food materials from the endosperm, and transports these materials to the growing regions of the embryo. Soon the food store is exhausted, and the endosperm and the cotyledon wither and drop off.
Germination is basically a process through which a new growth emerges after a period of dormancy. As a result of Germination, an embryonic plant within a seed grows into a plant.
Following are the types of Germination: - Hypogeal Germination: In this kind of Germination, the seed leaves or the cotyledons remain under the surface of soil.
- Epigeal Germination: In this type of Germination, the seed leaves grow above the ground on the new shoot.
-Cleistogeal Germination: A special leaf that has a central umbrella like stalk forms above the ground which protects the shoot from any damage. So the development of the shoot can not be seen.
