In this article we will discuss about the definition and conditions necessary for seed germination.
Definition of Seed Germination:
Germination is the process by which the embryo wakes up from the state of dormancy and takes to active life. This process, in fact, covers all the changes from the earliest sprouting of the seed till it established itself as an independent plant. A mature seed is living. But the embryo remains dormant.
The seed then contains only 10% to 15 % of water, and this low water content is one of the factors responsible for dormancy, When certain external conditions are satisfied the dormant embryo begins to grow.
Supply of water, favourable temperature, adequate supply of oxygen are main external conditions essential for germination, but, the seeds concerned must be viable, i.e. they must retain the power of germination. Light also has influence on germination of some seeds, but in most cases light regards germination at the early stages.
Condition Necessary for Seed Germination:
i. Water or Moisture:
The supply of water is very important for germination. The seeds absorb water and swell up. This swelling is the earliest sign of germination. Seed coats are softened and rupture easily to make way for the radicle and plumule to come out. Due to absorption of water the dormant protoplasm is activated for carrying on the vital functions.
It secretes enzymes or digestive juices, which convert the complex insoluble food matters stored up in the seed, either in the cotyledons or the endosperm, into their simpler soluble forms, so that the growing embryo may utilise them. Entrance of oxygen is also facilitated, and, as a result, the rate of respiration is accelerated.
An optimum rate of temperature is essential for germination. Protoplasm cannot carry on vital activities at a very low or at a very high temperature. There is a minimum below which seeds will not germinate and a maximum above which germination will not take place. The suitable temperature, of course, varies with the seeds. Most of the seeds usually show signs of germination when temperature varies from 25°C. to 30°C.
iii. Supply of Oxygen:
The dry seeds respire very feebly; with germination the rate of respiration markedly increases. So a constant supply of oxygen becomes essential.