The embryo inside a seed is quiescent until it germinates. Some seeds are dormant and will only become active after a certain environmental occurrence, such as fire, a certina length of tiem chilled, or light. As some species can stay dormant for tens of years until the right conditions occur, the ground contains a seed bank of ungerminated viable seeds which will become active in the right conditions. The seed first takes in a lot of water, which causes it to expand and break the seed coat as well as signalling the embry to start to grow again.
Food stored in the cotyledons is broken down by enzymes and moved to the embryo.
In barley, which is the most extensively studied species, the embryo produces gibberellin, a hormone, which stimulates the production of alpha-amylase in the aleurone layer, which is the thin outermost layer of the endosperm. The radicle emerges first from the seed, follwing by the upward-growing shoot tip. In many dicots, a hook forms in the hypocotyl which protects the vulnerable shoot and the large cotyledons in the journey out of the soil. The epicotyl develops foliage leaves which expand and photosynthesis, while the cotyledons wither and fall off once their food supply has been absorbed by the embryo. If the cotyledon is raised out of the soil, the mode of germination is called epigeal.