-o 



REACTION AT 45 AND I35 355 



whether any change in excitabihty had occurred on account 

 of fatigue, allowance for which was made by taking the 

 mean of the two responses for 45° at the beginning and at 

 the end of the series. 



Experiment 191. Geo-electric response at 45° and 135°. — 

 The following observations were made with the petiole of 

 Tropaeolum : the first and the third responses at 45° were 

 found to be 47 and 45 mm. respectively, the mean of the 

 two being 46 mm. The second 

 or intermediate response, taken 

 at 135°, gave 55 mm. The 

 excitatory reactions at 45° and 

 135° are thus in the ratio of 

 46:55, or as 1 : 1-2. In a second 

 series with a different specimen, 

 the first and the third responses 

 at 45° were both 25 mm. 

 (fig. 208). There was in this case 

 no fatigue. The intermediate 

 response at 135° was 31 mm. 

 The ratio of the excitatory 

 reactions at the two angles is 

 thus in the proportion of 25 : 31, 

 or as i:i-2. The excitation 

 at 135° is thus about 20 per 

 cent, greater than at 45°. 



The stem of Convolvulus was employed for the next 

 series of experiments. At 45° the excitatory deflection 

 was 26 divisions ; when the angle was increased to 135 °» 

 the deflection was enhanced to 31 divisions. That the 

 excitation at 135° was greater than at 45° was evidenced 

 in a convincing manner on return to the angle of 45°, 

 when the galvanometric spot of light was immediately 

 restored to almost the first deflection ; there was slight 

 fatigue, and the deflection was 25 divisions instead of the 

 former value of 26 divisions. The ratio of the two reac- 

 tions at 45° and 135° is thus 25-5 : 31, or i : 1-23. In the 

 second series of experiments the two excitatory deflections 



Fig. 208. Geo-electric response 

 at 45°, 135°, and 45°in sequence. 



