Moto-excit ability in Mimosa. 769 
at ordinary temperature was first applied on the pulvinus, and records were 
taken in the usual manner. Cooled glycerine was then applied and the 
record taken once more ; the results are seen in Figs. 8 and 9. In the 
former, the first response was normal at the temperature of the room, 
which was 32 0 C. ; the next two exhibit depression of excitability under 
moderate cooling ; the duration of application of moderately cooled 
glycerine is here indicated by the horizontal line below. On the cessation 
of application, the normal temperature was quickly restored, with the 
restoration of normal excitability. 
In the next record (Fig. 9) is shown the effect of a more intense cold. 
It will be noticed that the first effect was a depression, and subsequently, 
a complete abolition of excitability. The thick dots in the record represent 
applications of stimulus which proved ineffective. It will also be noticed 
Fig. 9. Effect of application ot more intense cold. Note sudden depression followed 
by abolition of excitability, also persistent after-effect. 
that even on the cessation of cooling, and the return of the tissue to normal 
temperature, the induced abolition of excitability persisted as an after-effect 
for a considerable time. I have likewise found that the after-effect of cold 
in abolishing the conduction of excitation is also very persistent. These 
experiments show that the variations of excitability in the plant often lag 
considerably behind the external changes which induce them. 
Effect of high temperature. It has been shown that the moto-excita- 
bility is enhanced by rising temperature ; there is, however, an optimum 
temperature above which the excitability undergoes a depression. This 
is seen in the following record (Fig. 10), where the normal response at 32 0 C. 
was depressed on raising the temperature to 43 0 C. ; the excitability was, 
however, restored when the plant was allowed to regain the former 
temperature. 
