448 



COMPARATIVE ELECTRO-PHYSIOLOGY 



ten minutes. In the case of Biophytum, for instance, the 

 required interval was found to be about five minutes. 



Taking a specimen of Biophytum, and employing the 

 method of determination which has been described, I found 

 successive values which were very consistent ; and, having 

 thus secured conditions which made it possible to obtain 

 exact results, I proceeded next to investigate the effects of 

 various factors such as fatigue, intensity of stimulus, and 

 temperature in modifying the velocity of transmission. 

 Before proceeding to describe these results in detail, how- 

 ever, it should be mentioned that, though the velocity of 

 transmission of excitation is constant in the same plant 

 under uniform conditions, yet this is not necessarily the case, 

 if the direction of conduction be reversed. In the petiole of 

 Biophytum, for example, the centrifugal velocity is always 

 higher than the centripetal, being about fifty per cent, 

 greater. 



Specimen I 



Specimen II 



In order to study the effect on velocity of progressive 

 fatigue, we may gradually shorten the interval of rest. The 

 velocity of transmission in the petiole of Biophytum when 

 fresh was found to be i'88 mm. per second in the centripetal 

 direction. Before making a second experiment on the same 

 specimen, an intervening period of rest of three minutes was 

 allowed. This was found to reduce the velocity slightly, it 

 being now r86 mm. per second. The following table shows 

 the results obtained by a series of five experiments on the 



