POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 6l 



the leaf. We shall now see whether a similar difference 

 exists between the electrical expressions of the positive and 

 negative turgidity-variations. 



In carrying out this experiment, I took a specimen of 

 Biophytum and applied stimulus at a distance from the par- 

 ticular leaflet whose responses were to be observed, arranging, 

 at the same time, for a simultaneous record of the mechanical 

 and electrical responses. It will be seen from fig. 46 that the 

 preliminary erectile twitch, due to the positive turgidity- 

 variation, has, as its concomitant, galvanometric positivity. 

 And this is followed in both records by its opposite : namely, 

 the contractile fall and the galvanometric negativity of true 

 excitation. 



It will thus be seen that the increase of internal energy, with 

 its positiye turgidity-variation, has, as its electrical expression, 

 galvanometric positivity. Besides this, the mere physical 

 movement of water in 

 the tissue gives rise to 

 a certain electrical varia- 

 tion of positivity, and 

 this can still be detected, 

 even after the tissue is 

 killed. The question of 

 how to discriminate what 

 proportion of the electro- 

 positivity was due to this 

 mere water - movement, 

 and what to the increase 

 of turgidity, associated 

 with the increase oT in- 

 ternal energy, I at first 

 found it very difficult to 

 decide. But I ultimately 

 succeeded in doing this 

 by bringing a plant to 

 a condition just short of 



FIG. 46. The Abnormal Positive preceding 

 the Normal Negative in Mechanical and 

 Electrical Responses in Biophytum 



x represents the moment of application of 

 stimulus. The upper is the mechanical 

 and the lower the ' electrical record. 

 The records downward indicate erection 

 of the leaf or galvanometric positivity. 



death, and thus abolishing its 



true excitatory reaction. In this condition, the responsive 



