418 Prof. Burdon-Sanderson and Mr. F. J. M. Page [Dec. 14, 



we propose to discuss the electrical condition of the leaf of Dionoea when 

 unexcited as compared with that of other non-excitable leaves. For our 

 present purpose it is sufficient to state as the general result of our 

 observations on this subject, first, that the part of the midrib which lies 

 nearest the two central sensitive hairs is positive to every other part of the 

 external surface of the leaf, but has usually the same potential as the 

 petiole and other inactive parts of the plant ; and secondly, that the 

 external surface, so long as the leaf is in vigour, is always positive to the 

 internal surface. These two statements, and particularly the second, 

 may be accepted with confidence ; but with reference to the first it must 

 be borne in mind that, inasmuch as unexplained differences of potential 

 often present themselves between symmetrical points of opposite lobes, 

 even in leaves which appear to be in a normal state, the determination of 

 the difference between any point and the midrib must necessarily be a 

 matter of great difficulty. 



Section 2. — Method, 



The .method employed in the present research differs from that 

 generally used in previous investigations relating to animal or plant 

 electricity in two important particulars, viz.: — first, in the adoption of 

 the electrometer as a means of investigating the electrical changes ; and 

 secondly, in the substitution of a constant for a variable potential. 



The electrometer used is that of Lippmann. We became acquainted 

 with this instrument through the kindness of Prof. Marey, who had 

 already adopted it in physiological investigations relating to animal 

 electricity. We append the following description of the instrument, 

 referring the reader for further information to the original paper of the 

 author*. 



The instrument consists of two glass tubes, A and B, fig. 4, of which 

 the former is drawn out into a Ccc-pillary |)oint y, the lufiien of which is 

 about millim. At the end opposite the capillary, A communicates 



* " Beziehungen zwischen den capillaren und electrischen Erscheinungen von G. 

 Lippmann," PoggendorflT's Annalen, 1873, Bd. 149. 



