Mr. W. A. Taylor, Chief of the Bureau of Plant Industry, has kindly furnished the photograph of the simple method of applying sulphate of copper. He says: "This reservoir, shown in the figure, was seriously affected with an abundant growth of a small green alga, which imparts a very pronounced piquant odor to the water. The reservoir was so badly infested that the disagreeable odor could be detected during the summer at a distance of half a mile. An application of copper sulphate at the rate of two-tenths of a part of sulphate to a million parts of water by means of the bags shown in the figure was sufficient to completely eradicate this trouble and during the succeeding years one or two applications during the summer have been sufficient to keep the reservoir in good condition."