In germination the cotyledons come above ground and form the first green leaves of the plant.
The embryo consists of an axis bearing two or more cotyledons and ending below in a radicle; it lies in a generally copious food-storing tissue (endosperm) which is the remains of the female prothallus.
In cases where the development of the embryo is advanced at the resting period, traces run from the cotyledons and determine the symmetry of the stele of the primitive axis, the upperpart of which often shows stem-structure, in some respects at least, and is called the hypocoty- ledonary stem or hypocotyl, while the lower part is the primary root .~-,
The hypocotyl usually elongates, by its cells increasing very greatly in the longitudinal direction both in number and size, so that the cotyledons are raised into the air as the first foliage-leaves.
In other cases this growing-point becomes active at once, there being little or no elongation of the hypocotyl and tbe cotyledon or cotyledons remaining in the seed.