Briefly stated, the main point of this article is as follows: In the best known works upon the parasitism of Botrytis and similar fungi too much importance has been ascribed to a cellulose-dissolving enzyme. Two stages in the process should be clearly distinguished: first, a poisoning and killing of the cells; and second, their disintegration and utilization as food by the fungus. The first effect appears to be produced by a substance which there are strong reasons for supposing to be oxalic acid, formed by the fungus as a by-product of its metabolism. Following this, a number of different enzymes are secreted which digest the various constituents of the tissue. The identity of these enzymes probably varies somewhat in different cases, and apparently more than one occurs which affects different forms of cellulose. The substance causing a marked swelling of the cell wall in the lily Botrytis, studied by Ward, and the turnip bacterium by Potter, appears to be an enzyme not ordinarily produced by Botrytis ci...