Agar is a Polysaccharide that solidifies almost anything that is liquid. This gelatinous substance is derived from seaweeds of the Rhodophyceae class. It is therefore used as a thickener and also for its water-holding capacity. It was chiefly used as an ingredient in deserts throughout Japan, but now the most important worldwide use of agar is as a gelatin-like medium for growing organisms in scientific and medical studies.