



^ On Electricity in Plants^ and on Y eg eto- terrestrial Currents. 91 



T 



The electric effects produced between the sap of leaves and 

 the same sap exposed a moment to contact with the air, may be 

 shown by piling up thirty leaves or so and compressing them 

 strongly, then inserting two needles, one on each side; on taking 

 out one and again restoring it to its place after some instants, it 

 gives negative electricity. This is due to the change in the sap 

 of the parenchyma on the needle that had been exposed. 

 \ The intensity of the current depends on the quantity and the 



Composition of the liquid in the leaves. Those of ivy produce 



a deviation of twenty to thirty degrees; those of the poplar of 



I Italy a little less or more strong, according as old or young leaves 



are used. Complex effects sometimes result from modifications 

 more or less profound which the sap undergoes in contact with 

 the air, and from the facihty with which the sap, on the exposed 

 needle, mixes with the surrounding medium, gaseous or liquid. 



It is possible therefore to compare leaves of different kinds in 

 this respect, such as elder and walnut. Twenty leaves of each 

 kind, in two piles, are put in contact by one of their surfaces and 

 compressed. A needle of platinum is inserted in each surface; 

 one of these needles is withdrawn and after some instants re- 

 placed. The direction of the deviation shows that the replaced 

 needle gives negative electricity. The amplitude of the devia- 

 tion depends on the nature of the leaf, as the following results 

 irom the walnut and elder show. 



The needle removed and again replaced in the elder gave for 

 deviation, on the first impulsion, for three trials, 13^, 13^, 11^, 

 and for three alternate trials with the walnut, 24^, 22^, 24^. 



These results show that the sap of the walnut undergoes a 

 jnore rapid change by contact with the air than that of the elder, 

 the current being nearly double in intensity. 



Leaves of poplar combined with those of walnut give results 

 still more marked. The leaves of poplar with regard to those of 



*^ W^^^^^ ^he relation of thirty to twenty. 



. " e can draw no conclusion from these results whilst we are 

 ignorant of the chemical composition of the different saps: we 

 J^nly know that all do not undergo the same alteration in equal 

 times. Such piles, made of series of leaves of different species, 

 'nay yet serve to educe facts of importance illustrating some 

 points in v^egetable physiology. If two such series o( leaves are 

 pnt m contact, and, before pressure, a plate of platinum connected 

 J^ith a multiplier is applied to each free face, we obtain the fol- 

 .^wuig results, with walnut, elder, linden, and orange, arranged 

 ni couples : 



Kind of electricity. Angle of deviation. 



I ^ Leaves of walnut, . . — ^35^ 



/ 



elder, . . + 

 2^ ^ Leaves of linden, . . + 



walnut, 



20^ 



I 



