

i 



IS 



r '■ 



* 



i 



' I 



y 



On Electricity i?i Plants^ and on Vegeto-terrestrial Currents. 89 



h 



and put the needle in place again upon the denuded surface, there 

 IS sensibly the same deviation. If another layer be removed, 

 there is still by a similar trial a deviation in the same direction 

 but a little less strong, or about 15 degrees. On continuing the 

 removal of the layers and making successive trials, the electric 

 effects take place in the same direction and do not cease until 

 only the cambium is left. All the parenchyma cortical layers 

 thus have a like effect; and does it therefore follow that the 

 layers united form a voltaic pile? Certainly not : the experi- 

 ments thus far made do not authorize this conclusion. 



However it may be, the cause which makes the bark a voltaic 

 couple and perhaps a pile, by the juxtaposition of the concentric 

 heterogeneous beds of which it consists, appears to be purely 



chemicaL 



pene 



cending sap rich in oxygen, while the liquid in the cortical 

 tissue, on traversing the green parts, is continually losing a por- 

 tion of this element by contact \yith the air. These two saps, 

 by reacting upon one another, through the medium of the inter- 

 vening tissues, necessarily cause electric effects; the ascending 

 sap, which is most oxygenated should act as an acid with 

 regard to the other, and develop positive electricity, while the 

 descending sap should disengage negative electricity. The in- 

 version in the bark and wood depending on the position of the 

 cellular tissue, is to be attributed to the nature of the liquids they 

 contain. 



^ The electricities disengaged when one of the needles is inserted 

 in the pith and the other in the parenchyma, have, I repeat it, a 



chemical ori 



gin 



for if the needles are withdrawn and while still 



. w*j^llj J J.WI 11 tilt/ IJtt^UIVO CllVv VV J LllUl V* •» »* »^*1V* 1. .««»V ^lr.»« 



covered with the sap are put into distilled water, the same effects 

 nearly, as to intensity, are obtained, effects which can be attributed 

 only to the reaction, upon the water, of the sap adhering to the 

 surface of the needles- 



In these experiments, for inserting the needles into the stem, 

 es|3ecially the woody part, I make small holes with a steel awl 

 covered with a thick layer of gold, so that no trace of oxydiza- 

 Dle metal can be introduced to occasion secondary electric effects. 



In herbaceous plants, like Cacti, Euphorbiacj &c., consisting 

 ahnost wholly of parenchyma, it is difficult to detect the electric 

 effects which are so distinct with stems provided with bark. 



As bearing upon this subject, I mention the following experi- 

 ments which wiJl show the rapidity with which the air reacts 

 upon the sap in the green parts and modifies its composition. 



The ascending sap being more oxygenated than the paren- 

 chyma sap, called the descending, ought to give out, by its action 

 upon the latter, positive electricity as before observed. If we 

 insert transversely under the epidermis, into the parenchyma, the 

 two platinum needles, one centimetre apart, there will be no 



Seco.nd Series, Vol. XII, No. 34.- July, 1851. - ' 12 



