Agar, also called agar-agar, is a complex gelatinous product prepared from the algae Gracilaria and Gelidium. Its powder dissolves in hot water, the solution forming a gel on cooling. It is used as a thickening agent or emulsifier in foods; as an adhesive; and as a medium for growing bacteria, mold, yeast, and other microorganisms; as a medium for tissue culture; and as a gel for electrophoresis. See also gum.