ormones are similar in type to the ethereal salts, or esters, which
constitute the natural essential oils that develop in many plants at this
stage of their growth. Hence, it seems probable that these changes in
plants which are maturing naturally may be hastened by the hormone action
of the esters and similar bodies which are developed in largest quantities
at that stage. It has been pointed out that the characteristic group which
is present in many natural glucosides is of the same general type as the
"hormone" substances which are used in the artificial stimulation of the
flowering or ripening changes. This fact, together with the possibility of
the liberation of greater percentages of these aromatic compounds from
their glucoside combinations at the later periods of plant growth, is
assumed, by some plant physiologists, to account for the change from
synthetic to degenerative processes at this stage of the plant's
development.

Further, it has been suggested that the autumnal coloration of leaves, and
their dropping from the stems of the plant, as well as the ripening of
seeds, is probably determined by the liberation in the plant, at that stage
of its growth, or as a result of changed climatic conditions at that
particular season of the year, of the hormones which either initiate or
hasten the special enzymic changes which distinguish the degenerative from
the synthetic processes of the plant.

Similarly, it has been suggested that parasitic fungi are able to penetrate
the host plant by first excreting "hormones" which bring about degenerative
changes in the tissues of the host plant and so make it more easily
penetrable by the hyphae of the parasite.

It will be seen that, in general, "hormones" are a type of substances
(possibly often present in plants in the form of glucosides) which are
supposed to stimulate the degenerative (or katabolic) vital processes in
contrast to the synthetic (or anabolic) changes. It has been suggested that
they do this in either one of two ways; namely, by favoring the
introduction of water into the protoplasm and so diluting the cell
contents, changing the osmotic pressure, etc.; or by bringing about a
separation of the colloidal layers, or films, of the protoplasmic complex,
producing a result similar to that produced by freezing the tissues. These
ideas have been suggested by studies of the changes in the equilibrium of
protoplasm when foreign substances are introduced into it. Th