re continues
to send commands to the stem to go on curving, in a way I can best
explain if I am allowed to make the plant express its sensations in
words. The tip says to the stem, "I am horizontal, therefore you must
bend upwards"; and when this order has been obeyed the tip says, "It is
of no use, I am still horizontal--go on bending." The result is that the
stem curls up into a spiral like a corkscrew or a French horn, as shown
in Fig. 4.

[Picture: Fig. 4.--Seedling Sorghums supported by their tips in
horizontal glass tubes]

These unfortunate plants are in the position of a convict on the
treadmill; their movements are, from their own point of view, absolutely
ineffectual and meaningless. The results are, however, of some
importance from our point of view, since they give clear support to the
theory which I have now attempted to place before you, namely, that the
percipient region is at the tip of the _Setaria_ seedling, and that by
what corresponds to a reflex action, the stimulus perceived by the tip is
transmitted to the motor region.

I should like to add a few words on the question how far the movement of
plants can be placed under the general laws deducible from the movements
of animals. Unfortunately, as soon as we attack this question we are
liable to enter regions where for the ignorant there are many pitfalls.
We are, in fact, face to face with the question whether in plants there
is anything in which we may recognise the faint beginnings of
consciousness, whether plants have the rudiments of desire or of memory,
or other qualities generally described as mental.

If we take the wide view of memory which has been set forth by S. Butler
{51a} and by Hering, we shall be forced to believe that plants, like all
other living things, have a kind of memory. For these writers make
memory cover the whole phenomena of life. Inheritance with them is a
form of memory, or memory a kind of inheritance. A plant or an animal
grows into the form inherited from its ancestors by passing through a
series of changes, each change being linked to the preceding stage as the
notes of a tune are linked together in the nervous system of one who
plays the piano. Or we may compare the development of an animal or plant
to the firing of a train of gunpowder, which completes itself by a series
of explosions, each leading to a new one. To use the language I have
been employing, each stage in deve