Seed dormancy: General survey of dormancy types in seeds, and dormancy imposed by external agents

Two basic kinds of dormancy have been distinguished by Bunning (1947): ectogenous, influenced by external factors such as light, temperature, water, etc.; and endogenous, conditioned by the internal constitution of the seed. Whether seeds possess either one or both of these types of rest depends upon two main factors, environmental influences and heredity. It should, however, be realized that the two influences are mutually dependent and sometimes cannot be separated.