Lower 凵 is the open-receptacle radical and the entry's indexing radical. It is the pit or vessel the upper sprout climbs out of; the whole character literally pictures growth pushing up and away from its container.
Upper 屮 depicts a tender shoot breaking the ground. Stacking two 屮 shapes originally pictured a plant emerging step by step out of an enclosure, which is where the meaning go out, come forth, exit comes from.
