312 PRESENT STATE OF ORGANIC ELECTRICITY. 



the instrument, the succulence of the tree, or the radial 

 distance of the layer into which the second electrode has 

 been inserted ; a current from without inwards is indicated, 

 the electrode in the pith being positive, that in the wood or 

 bark negative. 



If the one electrode be inserted close to the outside, and 

 the other be removed from the pith, and be reinserted from 

 place to place outwards, the current will diminish in intensity 

 as the second electrode approaches the cambium. Beyond 

 the cambium the current changes its direction and becomes 

 stronger. The current which now deflects the needle passes 

 along the wire from without inwards, indicating a positive 

 electric condition of the outer part of the parenchyma, and a 

 negative condition of the cambium. 



On removing a piece of bark, and applying the electrodes, 

 (which in this experiment should consist of platinum plates) 

 to its opposite surfaces, the current becomes very intense. The 

 piece of bark thus forms a voltaic couple, of which the ex- 

 terior or parenchymatous side is positive, and the interior, 

 covered by the cambium, negative. 



It would appear then that, from the pith to the cambium, 

 the woody layers are less and less positive in relation to the 

 pith ; whilst from the cambium to the cuticle, the parenchy- 

 matous layers are more positive, or at least comport themselves 

 as such in the production of derived currents. This inversion 

 of the electrical effects corresponds with the relative position 

 of the cellular texture in the bark and wood. In the bark, it 

 is on the exterior ; in the wood, in the interior ; in both it is 

 positive. 



In the notice by M. Wartmann, in the Bihliotheque JJni- 

 verselle de Geneve,* that observer states that " in uniting by 

 the galvanometer the layers of the stem where the liber and 

 cambium touch one another (and where many botanists admit 



* Bib. Univ. de Geneve, torn. xv. p. 301. 



