ELECTRICAL PHENOMENA AND METABOLISM OF ARUM SPADICES. 471 



through the tissue of a wave of excitation initiated at the point of 

 stimulation and sweeping successively over the proximal and distal 

 leading-off electrodes. 



Plates I., IV., XI. give typical records obtained with mustard, pea, 

 and maidenhair. 



In the experiment with a mustard seedling shown in Plate i. three 

 successive thermal stimuli were applied, at ten-minute intervals, to a 

 spot 3 cm. distant from the proximal leading-oflf electrode B. They 

 elicited three diphasic responses, of which the first and second are shown 

 in Plate i. A fourth stimulus was almost and a fifth quite ineffectual ; 

 but on moving the exciting wire to a distance of 10 mm. from B an 

 explosive double response was obtained on heating, followed by complete 

 inertia (Plate la, not shown). The interpolar distance of the leading-off 

 electrodes was about 1 cm. The maximum value of the response was 

 7/100 volt. 



Plate IV. (pea seedling) shows two successive responses, of which the 

 second is monophasic of more than .5/100 voltage, at 1 cm., 2-5 cm. 

 distance respectively. 



The value of 1/100 volt is augmented by about 35 per cent, at the 

 end of the expei'iment, showing that the electrical conductivity of the 

 tissue is increased. 



Plates XI. and xia show the curves obtained with an adult maidenhair 

 petiole. 



In this experiment the first stimulation was given at a distance of 

 12 cm. from the proximal electrode B, and caused a double diphasic 

 response, the first phase of which was rapid, the second prolonged and 

 of rather more than 1/100 voltage. There was an apparent latency of 

 response of about 30 seconds. 



Second and third stimuli at 6 cm. and 3 cm. elicited multiple responses 

 of considerable voltage. 



At the end of the experiment the electrical conductivity of the tissue 

 was found to be increased by more than 100 per cent. 



Plates vin. and ix. show an experiment with a broad bean 

 seedling in which a mechanical stimulus— i.e., the squeezing down of the 

 stimulating wire on the tissue, so causing a slight flexion — proved con- 

 siderably moi'e effective than the thermal. The first diphasic effect 

 (value over 2/100 \olt) was in response to pressure at 8 cm. distance. 

 Heating at this point caused only a slight response in the anomalous 

 direction. The second monophasic effect resulted from pi'essure at 4 cm. 

 distance and showed a latency of about 20 seconds. 



The interpretation of these diphasic electromotive changes as 

 indicative of an actual wave of excitation passing along the tissue is 

 borne out by the fact that the second phase of the response — i.e., that of 

 negativity at the distal electrode A — may be obliterated by previously 

 injuring the tissue at that spot. Such injury may be produced either by 

 strong tetanisation or by a section. 



Plate II. I'ecords an experiment v/ith mustard in which after distal 

 injury by section repeated monophasic deflections, indicative of galvano- 

 metric negativity of the uninjured spot, were obtained in response to 

 thermic stimulation. 



The transmission of electrical change may also be blocked by teta- 

 nising a portion of the tissue intermediate between the leading-off 

 electrodes and the point of thermal stimulation. Although the electrical 



