British Association, dOth Report, Cardiff, 1920.] 



[Plate I. 



Diagram of the circuit required for the systematic observation of the blaze- 

 currents of plants. B A are the unpolarisable electrodes by which the plant 

 currents are led off to the galvanometer G. Any accidental current or 

 current of injury of the plant is neutralised by the compensator. The wires 

 from the compensator are connected with the two ends of the three-plug key. 

 A single induction shock of given strength and direction can be short-circuited 

 or not by a plug at the first plug-hole. The plant can be short-circuited or 

 not at the second p4ug-hole. The galvanometer can be short-circuited or not 

 at the third plug-hole. 



Procedure. — Any accidental current or current of injury of the plant is 

 neutralised (and measured) by adjustments on the dials of the compensator. 

 The galvanometer is short-circuited at the third plug-hole. A break induction 

 shock of given strength and direction is sent through the plant by (closing 

 and) opening a contact-key in the primary circuit of the induction coil 

 (during closure of this key the secondary coil is short-circuited at the first 

 plug-hole to cut off the make shock from the plant). Immediately after the 

 break shock has passed through the plant, the galvanometer is unplugged at 

 the third hole; the blaze-current aroused by the previous break induction 

 shock now causes deflection of the galvanometer. The voltage of a deflection 

 is ascertained by comparison with the deflection given by 0.01 volt from the 

 compensator. The resistance in circuit is ascertained by comparison with the 

 deflection of 0.01 volt through 1.000,000 ohms. 



Illustrating 'Electromotive Phenomena in Plants.' 



[To face pnge 266. 



