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Agar (agar-agar, gum agar) is a natural polysaccharide derived from several species of marine red algae. Its primary use in the educational laboratory is as a solidifying (gelling) agent in microbiological media. For this purpose 15 grams of agar per liter of distilled or deionized water is the standard recipe. The agar powder is stirred into the water which is then heated to the boiling point (heat gently, stir constantly) to dissolve the agar. The resulting solution should be clear, lightly colored, and with little or no undissolved material.