256 RESEARCHES ON IRRITABILITY OF PLANTS 



at the anode at break only. This therefore constitutes 

 Type III., with the excitatory formula Km Am Ab. 



This type of excitation will be seen very clearly in the 

 automatic record which is given in fig. 125, taken with a 

 different specimen, where a single pulvinus was carried 

 through a complete cycle of kathode-make, kathode-break, 

 anode-make, and anode-break. It will be seen from the 

 record that while under 6 volts excitation took place at 

 kathode-make and anode-break, under a higher e.m.f. of 

 10 volts excitation not only took place at kathode-make 

 and anode-break but also at anode-make. Under a stronger 

 current Type II. has thus been transformed to Type III. 



Polar Reaction Type IV., Km Kb Am Ab 



Returning to the first specimen, the current was further 

 increased till an intensity was reached of 127 micro-amperes, 



Fig. 126. — Polar excitation Type IV., Km Kb Am Ab. 



and here was obtained another new type of reaction — 

 namely, excitation at both kathode and anode at both make 

 and break. The excitatory formula for this fourth type 

 is thus Km Kb Am Ab. 



In fig. 126 is exhibited an automatic record of this type 



