Semantic considerations

The discussion of seed structure and environment in relation to dormancy (Chapters 2 and 3) has shown that genetic variation in dormancy is expressed as a distribution of germinability over time. Seeds of nondormant genotypes germinate at maturity, or even before maturity, in a wide range of environmental conditions. Alternatively, at the time of maturity and abscission from the parent plant, seeds of dormant genotypes cannot be germinated within a wide range of temperatures in the presence of water, oxygen and light. With the passage of time the dormant seed becomes sensitive first to a narrow range of environmental conditions that promote germination. Later the range of each environmental factor, within which germination can occur, broadens until germination is limited only by water and extremes of temperature.

The term ‘after–ripening’ has often been used, loosely, to categorize the collective changes that seeds undergo with time as dormancy is lost. Afterripening has been used as a descriptor for loss of dormancy in a dry, stable, storage environment (Crocker & Barton, 1957), in a variable natural environment such as the soil (Baskin & Baskin, 1981), under conditions suited to optimal germination of non–dormant seeds (Simpson, 1966a), and ‘by undefined biochemical changes occurring in seeds’ (Baskin & Baskin, 1985).