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
, 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.
"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."
[Webster 1913 Suppl.]