Ever since the fermentation of silage has been studied and discussed the question of the agent causing the fermentation has been ill controversy. Some investigators have made the statement, based on evidence more or less incomplete, that microorganisms are solely responsible for the changes undergone by the ensiled forage. Other workers, who have based their conclusions on equally incomplete data, have held that in silage produced under proper conditions bacteria and yeasts do not figure to any appreciable extent, but that the plant cell itself is the cause of the chemical changes which take place in its constituents. Still other writers have sometimes taken sides on the subject without presenting any new data bearing on the problem.