Mature seeds of many species of woody plants may only be quiescent and will germinate immediately if planted under favorable environmental conditions. But seeds of most species exhibit some degree of dormancy and will not germinate even when placed under most favorable environmental conditions. Dormancy is a condition where seeds will not germinate even when the environmental conditions (water, temperature, and aeration) are permissive for germination. Seed dormancy may, however, be advantageous as well as disadvantageous. The prolonged chilling requirement for breaking dormancy of seeds of many temperate zone plants prevents germination until spring which ensures plant survival because earlier germinations would subject young plants to danger of injury by freezing. Similarly, in seeds of some desert plants inhibitors in the seed coats prevent germination. However, the inhibitors are leached out by sufficient rain to wet the soil thoroughly, insuring that seeds germinate only when there is enough soil moisture for establishment. In contrast, seed dormancy often is nuisance to nursery operators who wish to have large quantities of seeds germinate promptly in order to produce large and uniform crop of seedlings. The hormonal regulation of seed dormancy and methods of breaking it bear both physiological and practical importance and are discussed.
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