160 CDBRENT ELECTRICITY CHAP. XII. 



the parenchyma of the bark; that is to say, the 

 sap which circulates in their tissues is negative with 

 relation to the wood, to the pith, and to the earth, 

 and positive with regard to the cambium." .... 

 " The chemical actions are the first causes, it cannot 

 be doubted, of the electric effects observed in 

 vegetables." 



" In the roots," says Wartmannb, " the stems, the 

 branches, the petioles, and the peduncles, there 

 exists a central descending current, and a peripherical 

 ascending current ; I call them aidal currents." .... 

 " In most leaves the current proceeds from the 

 lamina to the nerves, as well as to the central parts 

 of the petiole and the stalk. In certain fleshy 

 .plants, it is directed from the medullary or cortical 

 portions of the stalk towards the mesophyUum, and 

 from the latter towards the superior and inferior 

 surfaces." . . . . " They arise from an electro-chemical 

 action between the liquid substances brought into 

 contact by the tearing of the tissues. The weak 

 residual current (which is the normal current) owes 

 its origin to the interposition of the porous vegetable 

 walls between juices of different concentration, and 

 proceeds through tliem from the densest to the least 

 dense liquid." 



The general conclusion that Professor Buff ap- 

 pears to have arrived at is the following : " TJie roots, 

 and all the inteittal portions of the plant filled with sap, 

 are in a permanently negative condition ; while the moist 

 E Philosophical Magazine, 185]. 



