It is scarcely conceivable that substances which vary so widely in composition as do the different types of glucosides can possibly all have similar physiological uses in plants. The cyanophoric glucosides, the pigment glucosides, the mustard oil glucosides, and the saponins, for example, can hardly be assumed to have the same definite relationships to the metabolism and growth of the plant. To be sure, they are alike in that they all contain one or more sugar molecules, and it is probable that the carbohydrates which are held in this form may serve as reserve food material, especially when the glucoside is stored in the seeds; but it is obvious that the simpler and more normal form of such stored food is that of the polysaccharides which contain no other groups than those of the carbohydrates. It seems much more probable that the physiological uses of glucosides depend upon their ability to form temporarily inactive "pairs" with a great variety of different types of organic compounds which are elaborated by plants for a variety of purposes. It has been noted that in most, if not all, instances, the glucosides are accompanied in the same plant tissue (although in separate cells) by the appropriate enzyme to bring about their hydrolysis and so set free both the sugar and the other characteristic component whenever the conditions are such as to permit the enzyme to come in contact with the glucoside. This occurs whenever the tissue is injured by wound or disease, and also during the germination process. Injury to the plant tissue seems to be a necessary preliminary to the functioning of the active components of the glucoside, except in the case of the seeds. This leads naturally to the supposition that at least some of these glucosides are protective or curative agents in the plant tissues. This conception is further supported by the facts that many of the non-sugar components of glucosides are bactericidal in character and that the glucosides commonly occur in parts of the plant organism which are otherwise best suited to serve as media for the growth of bacteria. Thus, it is known that in the almond, as soon as the tissue is punctured, amygdalin is hydrolyzed and all bacterial action is inhibited. Similarly, the almost universal presence of glucosides containing bactericidal constituents in the bark of trees insures natural antiseptic conditions for all wounds of the outer surfaces of the stem of the plant. In fact, it is easily conceivable that at least one of the reasons for the failure of the processes of decay of plant tissues to set in until after the death of the cells, is that during living, respiratory activity these antiseptic glucosides are so generally present in the tissues.