{50 deg. " 2 "

(4) {17 deg. " 80 "
{55 deg. " 0 "

(5) {17 deg. " 40 "
{60 deg. " 0 "

(6) {17 deg. " 60 "
{55 deg. " 0 "

[Illustration: FIG. 37.--THE GLASS CHAMBER CONTAINING THE PLANT
Amplitude of vibration which determines the intensity of stimulus is
measured by the graduated circle seen to the right. Temperature is
regulated by the electric heating coil R. For experiments on action
of anaesthetics, vapour of chloroform is blown in through the side
tube.]

#Electric heating.#--The experiments just described were, however, rather
troublesome, inasmuch as, in order to produce each variation of
temperature, the specimen had to be taken out of the apparatus, warmed,
and remounted. I therefore introduced a modification by which this
difficulty was obviated. The specimen was now enclosed in a glass
chamber (fig. 37), which also contained a spiral of German-silver wire,
through which electric currents could be sent, for the purpose of
heating the chamber. By varying the intensity of the current, the
temperature could be regulated at will. The specimen chosen for
experiment was the leaf-stalk of celery. It was kept at each given
temperature for ten minutes, and two records were taken during that
time. It was then raised by 10 deg. C., and the same process was repeated.
It will be noticed from the record (fig. 38) that in this particular
case, as the temperature rose from 20 deg. C. to 30 deg. C., there was a marked
diminution of response. At the same time, in this case at least,
recovery was quicker. At 20 deg. C., for example, the response was 21 dns.,
and the recovery was not complete in the course of a minute. At 30 deg. C.,
however, the response had been reduced to 7.5 divisions, but there was
almost complete recovery in twelve seconds. As the temperature was
gradually increased, a continuous decrease of response occurred. This
diminution of response with increased temperature appears to be
universal, but the quickening of recovery may be true of individual
cases only.

[Illustration: FIG. 38.--EFFECT OF TEMPERATURE ON RESPONSE
The response was abolished at the hot-water temperature of 55 deg. C.]

TABLE SHOWING DIMINUTION OF RESPONSE WITH INCREASING TEMPERATURE

(.01 Volt = 35 divisions)

Temperature Response

20 deg. 21
30 deg. 7.5
40 deg.