hypocotyl The region of the stem beneath the stalks of the seed leaves (cotyledons) and directly above the young root of an embryo plant. It grows rapidly in seedlings showing epigeal germination and lifts the cotyledons above the soil surface. In this region (the transition zone) the arrangement of vascular bundles in the root changes to that of the stem. Compare epicotyl.

hypocotyl Part of the embryonic shoot (plumule) or seedling located below the cotyledon and above the radicle (young root). See EPIGEAL.