Germination of seed includes all changes that take place from the time when dry, viable seed starts to grow when placed under suitable conditions of germination to the time when seedling becomes established on the substratum.
Conditions Necessary for seed Germination :
The conditions that are necessary for seed germination are as follows
A. External Factors :
1. Water : Water is of primary importance .in germination. A water-soaked seed will germinate, actual submergence may be harmful. When protoplasm absorbs the water, seed resumes vigorous physiological activities. The embryo bursts through the seed coats which are softened by imbibition of water.
2. Oxygen : In a germinating seed respiration and other physiological activities are more vigorous, hence oxygen is essential.
3. Suitable Temperature : Seeds usually germinate between 0°C to 50°C and the optimum usually lies between 25°C to 30°C.
B. Internal factors :
4. Foods and growth regulators : Food is necessary for growing embryo. This comes from cotyledons or endosperm. Some growth regulators are required for growth during germination.
5. Completion of rest period : Many seeds do not germinate immediately after harvest but undergo a period of rest which varies from plant to plant.
6. Viability : Viability is the germinating capacity of the seeds. Sometimes even perfectly viable seeds will not germinate even after being provided with suitable conditions of germination. Such condition is called dormancy. Dormancy may be due to hard seed coat impermeable to oxygen or water or there may be a low temperature requirement or the embryo may be immature at the time of harvest etc.