Electrical Phenomena in the /eo/' o/' JJiuiuea muscipula. 179 



2. hi a leaf \\ix.\x the petiole attached, the strength of the 

 current is determined by the length of the petiole cut off with 

 the leaf, in such a way that the shorter the petiole the greater is 

 the deflection. Thus in a leaf wit\L a petiole an inch long* I ob- 

 served a deflection of 40. I then cut off half, then half the 

 remainder, and so on. After these successive amputations, the 

 deflections were respectively 50, 05, 00, 120. If in this experi- 

 ment, instead of completely se\ering the leaf at each time, it is 

 merely all but di\'ided with a sharp knife, the cut surfaces remain- 

 ing in accurate apposition, the result is exactly the same as if the 

 severance were complete ; no further effect is obtained on separating 

 the parts. 



^..Effect of constant current directed through the petiole on tfte 

 leaf-current. — If the leaf is placed on the galvanometer electrodes 

 as before, and the petiole introduced into the circuit of a small 

 Daniell, a commutator being interposed, it is found that on 

 directing the battery-current do\^'n the petiole (i. e. frojn the leaf), 

 the normal deflection is increased ; on directing the current towards 

 the leaf, the deflection is diminished. 



4. Negative variation. — a. If, the leaf being so placed on the 

 electrodes that the normal leaf-current is indicated by a deflection 

 leftwards, a fly is allowed to creep into it, it is observed that the 

 moment the fly reaches the interior (so as to touch the sensi- 

 tive hairs on the upper surface of the lamina), the needle swings 

 to the right, the leaf at the same time closing on the fly. 



h. The fly having been caught does not remain quiet in the leaf ; 

 each time it moves, the needle again swings to the right, always 

 coming to rest in a position somewhat further to the left than 

 before, and then slowly resuming its pre\"ious position. 



c. The same series of phenomena present themselves if the 

 sensitive hairs of a still expanded leaf are touched with a camel- 

 hair pencil. 



cL If the closed leaf is gently pinched with a pair of forceps 

 with cork points, the effect is the same. 



e. If the leaf-stalk is placed on the electrodes, as before, with 

 the leaf attached to it, the deflection of the needle due to the stalk- 

 current is increased whenever the leaf is irritated in any of the 

 ways above described. 



/. If half the lamina is cut off and the remainder placed on the 

 electrodes, and that part of the concave surface at which the sen- 

 sitive hairs are situated is touched with a camel-hair pencil, the 

 needle swings to the right as before. 



g. If, the open leaf having been placed on the galvanometer 

 electrodes as in a, one of the concave surfaces is pierced with a 

 pair of pointed platinum electrodes in connexion u-ith the opposite 

 ends of the secondary coil of a Du Bois-Ueymond's induction 

 apparatus, it is observed that each time that the secondary cir- 

 cuit is closed the needle swings to the right, at once resuming 

 ils former position in the same manner as after mechanical 

 irritation. No difference in the effect is observable when the 



