mental arrangement
(fig. 15). It will be seen that in this case, where there could be no
possibility of shifting of contact, or variation of surface, there is
still the usual current of response.

I shall describe here a few crucial experiments only, in proof of the
physiological character of electric response. The test applied by
physiologists, in order to discriminate as to the physiological nature
of response, consists in finding out whether the response is diminished
or abolished by the action of anaesthetics, poisons, and excessively high
temperature, which are known to depress or destroy vitality.

I shall therefore apply these same tests to plant responses.

#Effect of anaesthetics and poisons.#--Ordinary anaesthetics, like
chloroform, and poisons, like mercuric chloride, are known to produce a
profound depression or abolish all signs of response in the living
tissue. For the purpose of experiment, I took two groups of stalks, with
leaves attached, exactly similar to each other in every respect. In
order that the leaf-stalks might absorb chloroform I dipped their cut
ends in chloroform-water, a certain amount of which they absorbed, the
process being helped by the transpiration from the leaves. The second
group of stalks was placed simply in water, in order to serve for
control experiment. The narcotic action of chloroform, finally
culminating in death, soon became visually evident. The leaves began to
droop, a peculiar death-discolouration began to spread from the mid rib
along the venation of the leaves. Another peculiarity was also observed.
The aphides feeding on the leaves died even before the appearance of the
discoloured patches, whereas on the leaves of the stalks placed in water
these little creatures maintained their accustomed activity, nor did any
discolouration occur. In order to study the effect of poison, another
set was placed in water containing a small quantity of mercuric
chloride. The leaves here underwent the same change of appearance, and
the aphides met with the same untimely fate, as in the case of those
subjected to the action of chloroform. There was hardly any visible
change in the appearance of the stalks themselves, which were to all
outer seeming as living as ever, indications of death being apparent
only on the leaf surfaces. I give below the results of several sets of
experiments, from which it would appear that whereas there was strong
normal response in the group of stalks kept