these seeds said to be photoblastic. e. Soil conditions : Germination of seed in its natural habit is influenced by soil conditions such as water holding capacity, mineral composition and aeration of the soil. ii.
Internal factors a. Maturity of embryo : The seeds of some plants, when shed will contain immature embryo. Such seeds germinate only after maturation of embryo. b.
Viability : Usually seeds remain viable or living only for a particular period. Viability of seeds range from a few days (Example: Oxalis ) to more than hundred years. Maximum viability ( years) has been recorded in lotus seeds. Seeds germinate only within the period of viability.
c. Dormancy : Seeds of many plants are dormant at the time of shedding. A detailed treatment is given below. II.
Seed Dormancy The seeds of most plants germinate under favourable environmental conditions but some seeds do not germinate when suitable conditions like water, oxygen and favourable temperature are not available. Germination of such seeds may be delayed for days, months or years. The condition of a seed when it fails to germinate even in suitable environmental condition is called seed dormancy . There are two main reasons for the development of dormancy: Imposed dormancy and innate dormancy.
Imposed dormancy is due to low moisture and low temperature. Innate dormancy is related to the properties of seed itself. . Factors causing dormancy of seeds: i.
Hard, tough seed coat causes barrier effect as impermeability of water, gas and restriction of the expansion of embryo prevents seed germination. ii. Many species of seeds produce imperfectly developed embryos called rudimentary embryos which promotes dormancy. iii.
Lack of specific light requirement leads to seed dormancy. iv. A range of temperatures either higher or lower cause dormancy. v.
The presence of inhibitors like phenolic compounds which inhibits seed germination cause dormancy. . Methods of breaking dormancy: The dormancy of seeds can be broken by different methods. These are: i.
Scarification : Mechanical and chemical treatments like cutting or chipping of hard tough seed coat and use of organic solvents to remove waxy or fatty compounds