202 RESEARCHES ON IRRITABILITY OF PLANTS 



key is turned to the left, the current is suddenly established, 

 the pulvinus being made kathode. The marker, which 

 has up to this moment been tracing a horizontal line, will 

 simultaneously mark an up-line, as shown in the record. 

 During the continuation of the current, the recorded signal 

 will appear as horizontal but at a higher level. The break 

 of kathode will be indicated by a down-line, stopping at 

 the original level. Anode-make is produced by turning 

 the key to the right, and this is indicated in the record as a 



down-line passing below the 

 horizontal level. A horizontal 

 line below the general level 

 indicates the continuation of 

 the anode. An up-line reach- 

 ing the general level indicates 

 the break of anode. 



Two records are reproduced 

 (fig. 107) exhibiting this polar 

 reaction under feeble current 

 in a second and more highly 

 sensitive specimen. The 

 effective e.m.f. was in this 

 case as low as 2 volts. It 

 will be seen that response 

 took place only at kathode- 

 make, there being no effect 

 either at kathode-break or 

 anode-make or break. The next response was taken under 

 the increased e.m.f. of 4 volts. The results depicted are 

 similar to those in the last case, the only difference being 

 the exhibition of an increased excitatory effect at kathode- 

 make due to the higher voltage. 



Excitation by Ascending and Descending Currents 



In the mono-polar method above described we have the 



effect of one particular electrode, quite distinct and isolated 



from the other. But when both the electrodes are placed 



Fig. 107. — Record of polar exci- 

 tation under feeble current. 

 Response seen to take place 

 only at make of kathode. 

 The line of signal below indi- 

 cates make or break of kath- 

 ode or anode. Up-line above 

 normal denotes kathode- 

 make ; down-line indicates 

 anode-make. 



