uggestions which have been put forward
and of the experimental work which is now in progress.

HORMONES

The term "hormone" was first used to designate certain stimulating
substances which are supposed to exist in the intestinal tracts of animals
and to cause the glands to elaborate and secrete their characteristic
enzymes. The supposed "hormones" are not themselves active in performing
the digestive functions of the glandular secretions, but are the exciting,
or stimulating, agents which cause the glands to secrete their active
enzymes.

The same term has been used, by certain plant physiologists, to designate
any agency, either external or internal, which stimulates plant protoplasm
to abnormal activity. It has been pointed out that there are a variety of
substances, which are themselves chemically neutral, that are powerful
stimulants of vital activity if used in only minute proportions, but are
powerful poisons if present in larger amounts. Many of the alkaloids act in
this way upon the animal organism; while chloroform, toluene, and even some
of the more complex hydrocarbons, act similarly upon the tissues of plants,
and ether vapor is known to be a powerful stimulant in accelerating the
flowering of plants and the ripening of fruits. It has been shown that the
vapors of all such substances readily penetrate the protoplasm of leaves,
seeds, etc., even when the same parts are impermeable to most mineral
salts, sugars, etc.; and that upon entrance to the protoplasm of a leaf, or
a seed, they tremendously stimulate its metabolic activity. These
hormones, as a class, are chemical substances which have very little
attraction for, or power of combination with water; and it has been
suggested that the ease with which they penetrate the protoplasm is due to
the fact that they are not held at the surface by combination with the
active water molecules which are present in the surface layer.

The principal effect which is supposed to be produced by these "hormones"
is the stimulation of the enzymic activity, particularly that of the
degenerative processes which take place late in the plant's life, at the
flowering or ripening periods. Many of the changes which take place
normally at ripening time, such as the change in color from green to yellow
or red and finally to brown or black, when the fruit or vegetable is fully
ripe, can be greatly accelerated by treatment with these substances.
H