Agar-agar

Agar-agar A`gar-a"gar, n. [Ceylonese local name.] 1. A fucus or seaweed much used in the East for soups and jellies; Ceylon moss ({Gracilaria lichenoides}). [1913 Webster]

2. A gelatinlike substance, or a solution of it, prepared from certain seaweeds containing gelose (such as Ceylon moss, {Gracilaria lichenoides} or other seaweeds of the genera {Gelidium}, {Ceramium}, {Pterocladia}, and {Eucheuma}), and used for solidifying growth media in the artificial cultivation of bacteria, or as a gelling agent in foods; -- usually called simply {agar}, by abbreviation.

Note: In composition it is predominantly a polysaccharide, and is not degraded by most bacteria. It thus almost completely replaced the earlier protein-based gelatins used for fixing bacterial colonies on culture plates, as the gelatins were often dissolved by the proteolytic enzymes common in bacteria.

Syn: gelose, agar. [Webster 1913 Suppl.]