170 RESEARCHES ON IRRITABILITY OF PLANTS 



Two out of the six leaves were subjected to the local action 

 of poison in the manner previously described : — 



(i) The testing stimulus was applied 15 minutes after 

 the application of poison. Excitatory impulse was found to 

 traverse all the leaves. Absorption of the particular poison 

 in the course of 15 minutes was too slight to induce any 

 marked depression of conductivity. 



(2) The experiment was repeated after half an hour 

 under the same stimulus as before — namely, the additive 

 effect of four shocks. The excitatory impulse was found 

 transmitted in the four normal, but arrested in the two 

 poisoned leaves. The block in the two leaves was, however, 

 forced by the application of a stronger stimulus due to the 

 additive effect of six shocks. 



(3) After two hours the conductivity of the poisoned 

 portion of the petiole was found practically abolished in 

 the two leaves. In these there was no transmitted effect, 

 even under the maximal stimulus of sixteen additive shocks. 

 The untreated leaves exhibited vigorous conduction, the 

 leaflets undergoing their serial fall with great rapidity. 



(4) In order to show that the absence of the transmitted 

 effect in the two leaves was due to local loss of conductivity 

 of the treated area, and not to the loss of motile sensibility 

 of the leaflets, stimulus was applied on the petiole beyond 

 the poisoned zone. The leaflets exhibited their normal 

 excitatory fall. 



Mercuric chloride solution. — After obtaining the block of 

 conduction by the action of copper sulphate, I tried the 

 effect of various other poisons, some of which were found 

 to be very virulent in their action. Mercuric chloride 

 solution, for example, abolished the power of conduction 

 in a much shorter time than copper sulphate. The only 

 drawback in the application of mercuric chloride is that it 

 exerts an excitatory action, the transmitted effect of which 

 induces fall of the sensitive leaflets, which often remain 

 persistently closed. 



Solution of -potassium cyanide. — There is no such exci- 



