Alpha-hemolysis, colonies are surrounded by a zone of intact erythrocytes that have a greenish color. Bacterial peroxide production, which results in the reduction of hemoglobin to methemoglobin, is generally responsible for this appearance. In beta-hemolysis, colonies are surrounded by a clear zone in which few or no intact erythrocytes can be found. Beta-hemolysis is caused by the action of hemolysins, erythrocyte-lysing enzymes, produced by the bacteria. In the photograph below, note how the cross-hatched pattern of the fluorescent panel in the ceiling is visible -- but only in the areas of hemolysis. In the photos below, the plate on the left shows beta-hemolysis and the plate on the right shows alpha-hemolysis.