The fungicides commonly employed are either in the form of -solutions (e. g., ammoniacal copper carbonate), suspensions (lime wash and Bordeaux mixture), and powders (sulphur). The use of spray mixtures or other fungicides has become world wide, and many problems of physiological interest have arisen respecting the effects of these substances on the plants which they are designed to protect. Bordeaux mixture has been under continuous observation for a period of about twenty years, and has proved interesting in both its toxic and other relations. The striking influence of this fungicide upon sound plants has awakened widespread interest, and numerous experiments have been made to determine the nature of the effects. Bordeaux mixture consists essentially of suspension films of copper hydroxid and certain other complex (mostly hydrated), largely insoluble, copper compounds; and when properly sprayed upon plant surfaces from the best nozzles, the particles are of extreme fineness, and there is realized aii almost perfect surface film. In spite of the greatest care in preparation and application, it is injurious to certain plants, such as the peach and the plum, and may not be used satisfactorily in such cases for disease control. In recent years it. has been shown that the extent of the injury to the apple and! other plants may be considerable, and Bordeaux mixture is; in such cases being supplanted. In this discussion, however, we may omit any detailed consideration of the toxic effects, of this mixture, a phase of the subject which has received much, consideration in this country from Bain (2), Crandall (6), Clark