LOCALISATION OF GEO-PERCEPTIVE LAYER 



483 



the probe, and the after-effect of wound on variation of 

 excitability. 



THE ELECTRIC PROBE. 



The wound-irritation is, however, reduced to a minimum 

 by making the probe exceedingly thin. A fine platinum 



Fig. 175. — The Electric Probe. Figure to the left represents one electric 

 contact made with sepal rf Nymphcea, and the other, with the flower-stalk by 

 means of the probe ; the included galvanometer is represented by a circle. 

 Figure to the right an enlarged view of the probe. 



wire 0*06 mm, in diameter passes through a glass tubing 

 drawn out into a fine capillary, and fused round one end 

 of the platinum wire which protrudes very slightly beyond 

 the point of fusion ; the exploring electrode is thus in- 

 sulated except at the protruded sharp point of the platinum 

 wire. The length of the capillary is about 6 mm., just 

 long enough to pass the experimental plant-organ trans- 

 versely from one end to the other ; the average diameter 

 of the capillary is about Olo mm. The other end of the 

 platinum wire comes out of the side of the tubing and is 

 led to one terminal of t^e galvanometer, the other being 

 connected with an indifferent point in the organ. The 

 probe can be gradually pushed into the plant-organ by 



