GLUCOSIDES 91 



THE PHYSIOLOGICAL USES OF GLTJCOSIDES 



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 physiolog- 

 ical 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 pur- 

 poses. 



It has been noted that in most, if not all, instances, the glu- 

 cosides 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 charac- 

 teristic 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 sup- 

 ported 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 other- 

 wise 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 



