102 



RELATION OF PLANTS TO ELECTRICITY 



Fill the tubes with zinc sulphate. The brushes should be arranged 

 so that the fluid will pass down through the quill handle and keep 



the hairs moist. Close up the upper 

 end of the tubes with a cork stopper 

 through which passes a rod or strip of 

 zinc which has been amalgamated with 

 mercury. The wires should be soldered 

 or closely bound to the zincs. Connect 

 one of these electrodes directly to the 

 galvanometer, and the other through 

 the key. Test the apparatus by bring- 

 ing the electrodes in contact with one 

 another ; if no movement is shown by 

 the galvanometer it is correctly ad- 

 justed. Open the key and touch one 

 electrode to the surface of a cotyledon 

 of any convenient plant, and the other 

 to the lower part of the stem. Note 

 deflection or movement of the electro- 

 meter. Cut shoots of woody plants and set lower end in a dish 

 of water. Place one electrode in water and the other on leaf. 

 Test the difference between the upper and lower sides of fleshy 

 leaves. Test the difference between the base of the midrib of a 

 large leaf and the middle of the blade to one side of the midrib. 

 158. Differences in Potential due to Metabolism. Secure a 

 glass tube 20 cm. long and 4 cm. in diameter. Fuse two glass 

 tubes 2 cm. in diameter to the sides about 2.5 cm. apart as in 

 Fig. 5. Fit caps of rubber over the lateral tubes and perforate 

 them to allow the passage of the electrodes, which should be 

 fitted air-tight. Fit the ends of the large tube with rubber stop- 

 pers and glass tubes to serve for the conduction of gases. Con- 

 nect one of these with a filter pump, and the other with a large 

 tube containing glass wool saturated with water. Disconnect 

 and put a seedling of pea 1 5 cm. long in the electric chamber, in 

 such position that the base and middle portion of the stem may 



Fig. 44. Non-polarizable 

 electrodes. After Verworn. 



