74 



COMPARATIVE ELECTRO- PHYSIOLOGY 



Or the same difference may be demonstrated by means 

 of mechanical response. A Mimosa is placed in a small 

 chamber and subjected to a sudden rise of temperature. 

 In consequence of this there is a preliminary excitatory 

 depression, followed, on the attainment of a steady rise, by 



gradually increasing erectile re- 

 sponse, which carries the leaf 

 above its original level. 



These opposed motile effects 

 can be shown, moreover, even 

 in the case of ordinary plants. 

 We take a spiral tendril of 

 Passiflora. In this, the outer 

 or convex surface is more ex- 

 citable than the inner or con- 

 cave, and external stimulus, 

 causing greater contraction of 

 this more excitable outer side, 

 induces a movement of un- 

 curling. This movement corre- 

 sponds to the excitatory fall 

 ^ Mimosa. The response by 

 increase of internal energy is, 



The dotted line represents the however, the opposite of this, 

 variable period of temperature 



change. Note the contractile and consists of a movement of 

 ^ated nd gr owth ie w n hich g fol: C s: C ^"S- When the tendril is 



The rate of growth became con- placed in a VCSSel of water, of 

 stant when the temperature be- ,. i ,, i 



came permanent at 35 C. whlch the temperature can be 



varied at will, a sudden rise of 



temperature causes a preliminary excitatory movement of 

 uncurling, followed by a movement of curling, when the 

 higher temperature has become steady. 



The electrical expressions of external stimulus and in- 

 ternal energy are similarly opposed. In fig. 85 (Chapter X.) 

 will be seen a record showing that sudden variation of 

 temperature, acting as an external stimulus, induced a 

 responsive galvanometric negativity, whereas steady rise of 



and 35 C. 



