calyptra

In mosses and liverworts, a layer of cells that encloses and protects the young sporophyte (spore capsule), forming a sheathlike hood around the capsule. The term is also used to describe the root cap, a layer of parenchyma cells covering the end of a root that gives protection to the root tip as it grows through the soil. This is constantly being worn away and replaced by new cells from a special meristem, the calyptrogen.