exposure to steam killed the plant (carrot) and abolished
the response.
Vibrational stimulus of 30 deg. applied at intervals of one minute; vertical
line = .1 volt.]

It will thus be seen that those modifications of vital activity which
are produced in plants by temperature variation can be very accurately
gauged by electric response. Indeed it may be said that there is no
other method by which the moment of cessation of vitality can be so
satisfactorily distinguished. Ordinarily, we are able to judge that a
plant has died, only after various indirect effects of death, such as
withering, have begun to appear. But in the electric response we have an
immediate indication of the arrest of vitality, and we are thereby
enabled to determine the death-point, which it is impossible to do by
any other means.

It may be mentioned here that the explanation suggested by Kunkel, of
the response being due to movement of water in the plant, is inadequate.
For in that case we should expect a definite stimulation to be under all
conditions followed by a definite electric response, whose intensity and
sign should remain invariable. But we find, instead, the response to be
profoundly modified by any influence which affects the vitality of the
plant. For instance, the response is at its maximum at an optimum
temperature, a rise of a few degrees producing a profound depression;
the response disappears at the maximum and minimum temperatures, and is
revived when brought back to the optimum. Anaesthetics and poisons
abolish the response. Again, we have the response undergoing an actual
reversal when the tissue is stale. All these facts show that mere
movement of water could not be the effective cause of plant response.

CHAPTER IX

PLANT RESPONSE--EFFECT OF ANAESTHETICS AND POISONS

Effect of anaesthetics, a test of vital character of response--Effect of
chloroform--Effect of chloral--Effect of formalin--Method in which
response is unaffected by variation of resistance--Advantage of
block method--Effect of dose.

The most important test by which vital phenomena are distinguished is
the influence on response of narcotics and poisons. For example, a nerve
when narcotised by chloroform exhibits a diminishing response as the
action of the anaesthetic proceeds. (See below, fig. 43.) Similarly,
various poisons have the effect of permanently abolishing all response.
Thus a nerve is killed by strong alkalis and stro