Cotyledons are the very first leaves that develop in a germinating seed. The embryo has a main axis called tigellum. The portion of the embryonal axis above the level of the cotyledons is called epicotyl and the portion of the embryonal axis below the level of the cotyledons is called hypocotyl. At its lower end, the embryonal axis has a radicle (the part of the plant embryo that develops into the young primary root after seed germination) and the root cap enclosed within an undifferentiated sheath called coleorhiza. So, coleorhiza acts as a protective covering for the young root.
Epicotyl has a shoot apex and a few leaf primordia enclosed in a hollow foliar structure called coleoptile. The coleoptile acts as a protective covering for the young shoot.
Monocot plants have a single cotyledon. In the grass family, it is known as the scutellum.
The part of the plant embryo that develops into a shoot after seed germination is called plumule.