The outer boundary of the stem is a single layer of cells, called the epidermis (Greek: epi, “upon”; derma, “skin”). The cuticle is a layer of waxy cutin superimposed on and impregnating the outer walls of epidermal cells. It reduces evaporative water loss and protects the stem against invasion by molds. Stems may remain smooth, or glaucous (Greek: glauco, “bluish gray,” from the presence of wax), or become hairy, or pubescent (Latin for “downy”), when numerous epidermal hairs grow from their surfaces.
