on the sudden
appearance of frost. In the previous week, when the temperature was
about 10 deg. C., I had obtained strong electric response in radishes whose
value varied from .05 to .1 volt. But two or three days later, as the
effect of the frost, I found electric response to have practically
disappeared. A few radishes were, however, found somewhat resistant, but
the electric response had, even in these cases, fallen from the average
value of .075 V. under normal temperature to .003 V. after the frost.
That is to say, the average sensitiveness had been reduced to about
1/25th. On warming the frost-bitten radish to 20 deg. C. there was an
appreciable revival, as shown by increase in response. In specimens
where the effect of frost had been very great, i.e. in those which
showed little or no electric response, warming did not restore
responsiveness. From this it would appear that frost killed some, which
could not be subsequently revived, whereas others were only reduced to a
condition of torpidity, from which there was revival on warming.

I now tried the effect of artificial lowering of temperature on various
plants. A plant which is very easily affected by cold is a certain
species of Eucharis lily. I first obtained responses with the leaf-stalk
of this lily at the ordinary temperature of the room (17 deg. C.). I then
placed it for fifteen minutes in a cooling chamber, temperature -2 deg. C.,
for only ten minutes, after which, on trying to obtain response, it was
found to have practically disappeared. I now warmed the plant by
immersing it for awhile in water at 20 deg. C., and this produced a revival
of the response (fig. 35). If the plant be subjected to low temperature
for too long a time, there is then no subsequent revival.

[Illustration: FIG. 35.--DIMINUTION OF RESPONSE IN EUCHARIS BY LOWERING
OF TEMPERATURE
(_a_) Normal response at 17 deg. C.
(_b_) The response almost disappears when plant is subjected to -2 deg. C.
for fifteen minutes.
(_c_) Revival of response on warming to 20 deg. C.]

I obtained a similar marked diminution of response with the flower-stalk
of Arum lily, on lowering the temperature to zero.

My next attempt was to compare the sensibility of different plants to
the effect of lowered temperatures. For this purpose I chose three
specimens: (1) Eucharis lily; (2) Ivy; and (3) Holly. I took their
normal response at 17 deg. C., and found that, generally speaking, they
attained a f