Seed germination is defined as the sum of events that begin with hydration of the seed and culminate in emergence of the embryonic axis (usually the radicle) from the seed coat. There are two types of germination:

Epigeal Germination:

Epigeal germination is the type of germination in which the cotyledons rise out of the soil due to the elongation of the hypocotyl. The hypocotyl is the part of the stem of an embryo plant beneath the stalks of the cotyledons.

Hypogeal germination:

Seed germination in dicots in which the cotyledons remain below the soil surface. In this type, the epicotyl elongates and the hypocotyl does not raise the cotyledons above ground. The epicotyl, which is the region of an embryo plant above the cotyledon, grows longer while pushing the plumule out of the soil.

Figure 20. Epigeal and hypogeal germination