ns yield a variety of sugars,--glucose, galactose,
arabinose, and sometimes fructose, and even other pentoses--and a group of
physiologically active substances, known as "sapogenins."

The more toxic forms of these glucosides are known as "sapotoxins."

The chemical composition of the saponins varies so widely that it is
scarcely possible to cite typical individuals. Sarsaparilla, the dried root
of smilax plants, contains a mixture of non-poisonous saponins, from which
at least four individual glucosides have been isolated and studied. Corn
cockle contains a highly poisonous sapotoxin which, on hydrolysis, yields
four molecules of a sugar and one of sapogenin, C_{10}H_{16}O_{2}. Other
sapotoxins are obtained from the roots of soapwort and from several species
of _Gypsophila_. Digitonin and digito-saponin are glucosides of this type
which are found in the extracts from various species of _Digitalis_.

THE PHYSIOLOGICAL USES OF GLUCOSIDES

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,