286 COMPARATIVE ELECTRO-PHYSIOLOGY 



tropical elephant creeper (Pothos), the rich green of which is 

 barred by longitudinal streaks of milk-white. This dis- 

 tribution of colour is found even in the youngest and most 

 vigorous leaves. The question whether such colouring was 

 accidental or associated with physiological differences could, 

 I thought, be determined by the delicate mode of investiga- 

 tion which was now at my disposal. On making electrical 

 connections, then, with the green and white portions of a leaf, 

 I found that the natural current of rest was from white to 

 green through the tissue, and, on further testing the differ- 

 ential excitability in the usual manner, the responsive current 

 was observed to flow from the green to the white. This 

 showed that pallidity was here associated with a depressed 

 physiological condition. 



