70 deg. " v 7 " --
----->

[Illustration: FIG. 40.--RECORDS OF RESPONSES IN EUCHARIS LILY DURING
RISE AND FALL OF TEMPERATURE
Stimulus constant, applied at intervals of one minute. The temperature
of plant-chamber gradually rose on starting current in the heating
coil; on breaking current, the temperature fell gradually.
Temperature corresponding to each record is given below.
Temperature rising: (1) 20 deg., (2) 20 deg., (3) 22 deg., (4) 38 deg., (5) 53 deg.,
(6) 68 deg., (7) 65 deg..
Temperature falling: (8) 60 deg., (9) 51 deg., (10) 45 deg., (11) 40 deg., (12) 38 deg..]

#Point of temperature maximum.#--We have seen how, in cases of lowered
temperature, response is abolished earlier in plants like Eucharis,
which are affected by cold, than in the hardier plants such as Holly and
Ivy. Plants again are unequally affected as regards the upper range. In
the case of Scotch kale, for instance, response disappears after ten
minutes of water temperature of about 55 deg. C., but with Eucharis fairly
marked response can still be obtained after such immersion and does not
disappear till it has been subjected for ten minutes to hot water, at a
temperature of 65 deg. C. or even higher. The reason of this great power of
resistance to heat is probably found in the fact that the Eucharis is a
tropical plant, and is grown, in this country, in hot-houses where a
comparatively high temperature is maintained.

[Illustration: FIG. 41.--CURVE SHOWING VARIATION OF RESPONSE IN EUCHARIS
WITH THE RISE AND FALL OF TEMPERATURE]

#The effect of steam.#--I next wished to obtain a continuous record by
which the effects of suddenly increased temperatures, culminating in the
death of the plant, might be made evident. For this purpose I mounted
the plant in the glass chamber, into which steam could be introduced. I
had chosen a specimen which gave regular response. On the introduction
of steam, with the consequent sudden increase of temperature, there was
a transitory augmentation of excitability. But this quickly disappeared,
and in five minutes the plant was effectively killed, as will be seen
graphically illustrated in the record (fig. 42).

[Illustration: FIG. 42.--EFFECT OF STEAM IN KILLING RESPONSE
The two records to the left exhibit normal response at 17 deg. C. Sudden
warming by steam produced at first an increase of response, but five
minutes