mucilage (myōˈsəlĭj) [key], thick, glutinous substance, related to the natural gums, comprised usually of protein, polysaccharides, and uranides. It swells but does not dissolve in water. Mucilage is secreted by the seed covers of various plants, including marsh mallows and flaxes and certain seaweeds; it is the chief constituent of agar. In the plant it sometimes serves to check the loss of water to aid germination, to facilitate seed dispersal, and to store food. It is used in medicine as an emollient and a demulcent. Mucilage is employed also as an adhesive, and the term is extended to include other slimy adhesives, especially solutions of gum, such as tragacanth mucilage.