PLANTS UNDER MECHANICAL STIMULUS. 297 
conditions of excessively high or low temperature and is near 
its death-point. 
Fig. 19. 
Abnormal positive response converted into normal negative. 
Influence of Temperature on Plant- Response. 
It is well known that for every plant there is an optimum 
temperature most favourable to its vital activity. Above and 
below, at the maximum and the minimum, the vital activity is 
arrested, and if the plant is kept for long time under these 
unfavourable conditions it is apt to be killed. 
I tried to determine whether the undoubted changes induced 
by temperature in the vital activity of the plant affected the 
electrical response. 
Effect of very Low Temperature.—After severe frost, 1 found 
specimens of plants, which usually give strong response, become 
irresponsive. I then tried the effect of artificial lowering of 
temperature. A plant which is easily affected by cold is the 
Eucharis lily. I first obtained strong responses of the leaf- 
stalk at ordinary temperature of the room(17°C.). After cooling 
the stalk to —2° C. for 15 minutes, the response practically 
disappeared. On warming it again, the response reappeared. 
But the action of too long-continued cold caused a permanent 
abolition of response. My next attempt was to find the 
comparative liability of different species of plants to the effect 
of low temperature. For experiment I chose (1) Eucharis lily 
(leaf-stalk), (2) ivy-stem, and (3) stems of holly. I obtained 
the record of their normal responses at 17° C. I then placed 
them in an ice-chamber for 24 hours, and took their records 
once more. I found the electric responsiveness of the Eucharis 
lily, known to be susceptible to the action of cold, had 
oe 2 
LINN. JOURN.—BOTANY, VOL. XXXY. aA 
