* 



Petiole- Pulvinus Preparations of Mimosa pudica. 219 



The specimen was vigorous and the response obtained was found to be a 

 maximum. The stem bearing the leaf was cut at the moment marked in the 

 record with a cross, and water was applied at the cut end. The effect of 

 section was to cause the maximum fall of the leaf, with subsequent recovery. 

 After this, successive responses to uniform stimuli at intervals of 15 minutes 

 show, in (1) of fig. 3, that a depression of excitability has been induced 



Fig. 3. — Variation of excitability after section. (1) Immediate effect ; (2) variation of 

 excitability in a second specimen during 50 hours : (a) response 4 hours after section ; 

 (b) after 24 hours ; (c) after 49 hours. 



owing to the shock caused by section. In course of an hour, however, the 

 excitability had been restored almost to its original value before the section. 

 This was the case with a vigorous specimen, but with less vigorous ones a 

 longer period of about three hours is required for restoration. In certain 

 other cases the response after section exhibits alternate fatigue ; that is to say, 

 one response is large and the next feeble, and this alternation goes on for a 

 length of time. The isolated specimen, generally speaking, attains a uniform 

 sensibility after a few hours, which is maintained, with very slight decline 

 under constant external conditions, for about 24 hours. On the third day 

 the fall of excitability is very rapid, and the sensibility declines to zero in 

 about 50 hours after isolation (fig. 3 (2)). We may describe the whole cycle 

 of change as follows : by the shock of operation the isolated preparation is 



T 2 



