496 Electrical Phenomena in the leaf of 'Dionaea muscipula. [Nov.20^ 



and the petiole introduced into the circuit of a small Daniell, a com- 

 mutator being interposed, it is found that on directing the battery- 

 current down the petiole (i. e. from the leaf), the normal deflection is in- 

 creased ; on directing the current towards the leaf, the deflection is di- 

 minished. 



4. Negative variation. — a. If, the leaf being bo placed on the elec- 

 trodes 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 sensitive hairs on the upper 

 surface of the lamina), the needle swings to the right, the leaf at the 

 same time closing on the fly. 



b. 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 previous 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. 



d. 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 in- 

 creased 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 elec- 

 trodes, and that part of the concave surface at which the sensitive 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 with the opposite ends of the secondary 

 coil of a Du Eois-Eeymond's induction apparatus, it is observed that 

 each time that the secondary circuit is closed the needle swings to the 

 right, at once resuming its former position in the same manner as 

 after mechanical irritation. No difference in the effect is observable 

 when the direction of the induced currents is reversed. The observation 

 may be repeated any number of times ; but no effect is produced unless an 

 interval of from ten to twenty seconds has elapsed since the preceding irritation. 



h. If the part of the concave surface of the leaf which is nearest the 

 petiole is excited, whether electrically or mechanically, the swing to the 

 right (negative variation) is always preceded by a momentary jerk of the 

 needle to the left, i. e. in the direction of the deflection due to the 

 normal leaf-current ; if any other part of the concave surface is irritated, 

 this does not take place. 



i. Whether the leaf is excited mechanically or electrically, an interval 

 of from a quarter to a third of a second intervenes between the act of 

 irritation and the negative variation. 



