CHARACTER OF TRANSMITTED IMPULSE 173 



pulvinus but to the block of conductivity of the petiole, 

 a fourth record was taken under direct stimulation, which 

 proves that the motile excitability of the leaf had remained 

 unimpaired. 



Mercuric chloride solution. — A series of records was next 

 taken exhibiting the effect of mercuric chloride solution. 

 The power of conduction was found arrested after a period 

 of application so short as 10 minutes. The record obtained 

 was very similar to that given in the next figure. 



Potassium cyanide solution. — I next took a series of 

 records which exhibited the effect of strong solution of 



Fig. 95. — Abolition of conductivity by the action of potassium cyanide : 

 (i) Normal record ; (2) Arrest of conduction after application for 

 five minutes ; (3) Record showing arrest of impulse due to very 

 strong stimulus ; (4) Record of direct stimulation. 



potassium cyanide. Record i, fig. 95, gives the normal 

 transmission period. Record 2 was taken, as stated before, 

 after allowing 20 minutes for recovery. The poisonous 

 solution was however applied 15 minutes after the pre- 

 vious record ; hence in the second record we see the effect of 

 application of potassium cyanide for a period of 5 minutes 

 only. The effect of this poison on the conductivity of 

 petiole of Mimosa was so great that even with such a 

 short application the transmission of excitation caused 

 by maximal stimulus of 2 units was completely blocked. 



