Seed and Sowing- Factors Affecting the Germination
External Factors:
1.Moisture: It enables the resumption of physiological activities, swelling of seed due to absorption of moisture & causes bursting of seed coat & softening the tissue due to which embryo awakes & resumes its growth.
2. Temperature: A suitable temperature is necessary for proper germination. Germination does not take place beyond certain minimum & maximum temperature i.e. 0⁰C & above 50⁰C. Optimum temperature range for satisfactory germination of seed is 25 to 30⁰C.
3. Oxygen: It is essential during germination for respiration & other physiological activities which are vigorous during the process.
4. Light: It is not considered as essential for germination & it takes place without light. The seedlings grow more vigorously during darkness rather in light. However, for survival of germinating seedling, light is quite essential.
5. Substratum: It is the medium used for germinating seeds. In the laboratory, it may be absorbent paper (blotting paper, towel or tissue paper), soil & sand. Substratum absorbs water & supplies to the germinating seeds. It should be free from toxic substances & should not act as medium for growth of micro-organisms.
Internal Factors:
1. Food & Auxins: An Embryo feed on the stored food material until young seedlings prepares its own food. Auxins are the growth promoters, hence quite essential during the germination.
2. Viability: All seeds remain viable for certain definite period of time and thereafter embryo becomes dead. It depends on maturity of seed, storage conditions & vigour of parents and type of species. Generally, it is for 3-5 years and they remain for more than 200 years also as in lotus.
3. Dormancy: It is the failure of mature viable seed to germinate under favorable condition of moisture. Many seeds do not germinate immediately after their harvest, they require rest period for certain physiological activities.