Seed dormancy is the internal or innate inhibition of germination of normal or viable seed even when present under most favourable conditions required for its germination. Dormancy is of following types
1. Immature Embryo : The embryo is not fully developed at the time of seed shedding, e.g., Ginkgo.
2. After Ripening : After ripening, the seeds require an interval of ripening before they attain power to germinate, e.g., Maize, Barley.
3. Tough Seed Coats : The seed coats are hard and provide mechanical resistance to the growth of embryo, e.g., Capsella.
4. Inhibitors: They are chemical substances which do not allow the seeds to germinate, e.g., Cucurbita