This provides a pool of ungerminated seeds in the soil which is one reason vegetation appears so rapidly after environmental disruptions. Hydration causes the seed to swell and rupture the seed coat.
Hydration also triggers metabolic changes in the embryo that cause it to resume growth.
Storage materials of the endosperm or cotyledons are digested by enzymes and the nutrients transferred to the growing regions of the embryo. The next step in the change from a seed to a seedling is the shoot tip breaking through the soil surface. In many dicots, a hook forms in the hypocotyl . Growth pushes the hypocotyl above ground. Light stimulates the hypocotyl to straighten, raising the cotyledons and epicotyl.