Seed Germination and Dormancy

Seed germination is simply the activation and growth of the embryo packed inside a seed into a full seedling, once conditions such as water, oxygen and temperature become favourable. But not every seed germinates as soon as conditions are suitable - some remain ungerminated for days, months or even years despite favourable conditions, a state called seed dormancy. Dormancy has two broad root causes: imposed dormancy, which comes from external limitations like low moisture or low temperature, and innate dormancy, which comes from the intrinsic properties of the seed itself. Several specific factors can cause innate dormancy: a hard, tough seed coat that physically blocks water and gas exchange and restricts the embryo's expansion; a rudimentary (imperfectly developed) embryo that isn't yet ready to grow; a specific light requirement the seed hasn't been given; a temperature range, whether too high or too low, that suppresses germination; and the presence of germination-inhibiting compounds such as phenolics. Dormancy is broken using five distinct techniques: scarification (mechanically or chemically breaking down a hard seed coat, e.g. by cutting, chipping, or dissolving waxy/fatty coatings with organic solvents); impaction (vigorously shaking seeds whose micropyle is blocked by cork cells, to dislodge the plug); stratification (holding seeds of rosaceous fruits like apple, plum, peach and cherry in cold, moi …