242 Existence of electric Currents 



centre, on a plane at right angles to the axis of the fruit. 

 To determine how far these currents of electricity were 

 owing to the different structures of the fruit, or to a 

 difference in composition of the sap or proper juices in dif- 

 ferent parts, M. Donne divided a plum transversely into two 

 different portions, and expressed the juice from each into 

 two glasses, connected only by a slip of moistened bibulous 

 paper ; then, on immersing the wires of the galvanometer 

 into the two glasses, the magnetic needle immediately de- 

 viated in the same manner as if they had been inserted into 

 the entire fruit; proving that the electric current was owing 

 to a difference in chemical composition between the juice from 

 the apex and base of the same fruit. Thus, in the case of 

 the plum, the juice from its upper half (apex) acted on the 

 galvanometer like an alkali, and that from its lower half, or 

 base, like an acid. These experiments demonstrate most 

 satisfactorily the existence of electric currents in some kinds 

 of vegetable tissue, although they fail to show how far these 

 currents depend upon the vital action of the vegetable struc- 

 ture. The researches of M. Pouillet* serve, however, to 

 throw some light on this part of our subject. This philoso- 

 pher took twelve capsules of glass, 8 in. or 10 in. in diameter, 

 carefully varnished with gum-lac, and placed them on a table 

 also covered with the same resin ; he then filled them with 

 vegetable mould ; and, having connected each of them by 

 metallic wires, he planted in each some seeds (as of wheat, 

 lucerne, wallflower, garden cress, &c), and then connected 

 one of the capsules with the upper plate of a condenser, the 

 lower being connected with the earth ; insulation being pre- 

 served, as carefully as possible, by keeping the air of the 

 room free from moisture (by exposing in the apartment large 

 quantities of quicklime). In the course of two days, the seeds 

 swelled, and the infant plants extended about a line beyond 

 the envelopes of the seed ; but no electricity could be detected 

 by the aid of the condenser. When the plumules had fairly 

 extended into the atmosphere, and completely cleared the 

 earth which had covered them, electricity was readily de- 

 tected ; for, on separating the plates of the condenser, the 

 gold leaves of an electrometer, with which it was in commu- 

 nication, diverged to a considerable extent. This electricity 

 was constantly negative ; from which circumstance M. Pouillet 

 supposed, with great probability, that, during the action of 

 the oxygen of the atmosphere upon the cotyledons of the em- 

 bryo, the gas disengaged carries off the positive electricity, 



* Annales tie Cliimie et tie Physique, torn. 35. p. 414. 



