ABSTRACT - Dormancy is presented as a physiological state in which germination is blocked by a
seed-related mechanism, as opposed to lack of germination due to inadequate environmental conditions.
This state can be induced by environmental and/or maternal effects during seed development or after
dispersal, and can consist of many different mechanisms, which arrest continued development at any one
of the steps necessary for seed germination (imbibition, activation of metabolism, visible growth). Thus
dormancy and germination are concurrent processes, since the dormant seed can progress to different
stages in the germination sequence depending on the point(s) at which development is blocked. Both the
quantitative aspects of dormancy and the cyclic variations in degree of dormancy which are observed in
natural seed populations can be explained by quantitative variations in levels of growth promoters,
inhibitors, receptors or other metabolites or physiological processes which respond to low and high
temperatures, drying, photoperiod, light quality and intensity, or other environmental factors. Breaking
dormancy, or successful completion of the germination process, requires that all the necessary elements
for germination be in place and functioning; the absence or block of a single essential process is sufficient
to cause dormancy. The ecological importance of dormancy resides principally in the blockage of
germination when environmental conditions are adequate for germination but the perspectives for
successful establishment and growth of the seedling are not promising (when conditions are not adequate
- temperature or water is limiting, for example - the seed will be quiescent and germination will not occur
even in the absence of dormancy). Dormancy may also be important in distributing the germination of a
seed lot over time or space. Tolerance of adverse conditions may be improved by dormancy but does not
depend on dormancy as such.
ADDITIONAL INDEX TERMS: Seed dormancy, germination.