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86 Oh Electricity in Plants^ and on Vegeto-terrestrial Currents. ^ ^ 



vegetable organization. The bark consists independently of the 

 parenchyma, of epidermis, laticiferous vessels and cortical fibres. 

 The wood is formed of medullary rays, of woody fibre, and pith. 

 The bark like the wood contains a cellular and a fibrous part but 

 in inverse position. The parenchyma which is analogous to the 

 pith occupies the exterior of the bark, whilst the pith is at the 

 centre. This inverse position corresponds, as will be seen, to 

 inverse electric effects. 



As each stem or branch is composed of an uninterrupted series 

 of concentric heterogeneous layers, their successive contacts ought 

 to give rise to electric currents proceeding from the unlike char- 

 acter of the liquids moistening these layers. These effects are 

 rendered sensible — 1, by the aid of platinum needles introduced 

 into two contiguous or more or less distant layers, reacting upon 

 the neighboring layers; 2, by collecting with a condenser the 

 electricity carried off from the plant by the vapor of water exhaled 

 by the leaves and by the oxygen proceeding from the decompo- 

 sition of carbonic acid under solar influence ; 3, by using platinum 

 needles in order to ascertain the simultaneous electric states of the 

 plant and the earth. 



The moisture of the earth enters the roots by their extremity 

 through endosmosis and capillarity, passes into the cellules situ- 

 ated above, and reaches the stem where the ascending move- 

 ment is continued : it dissolves some portions of substances in its 

 course, increases in density, and constitutes then what is called 

 sap. The ascent of the sap is due not only to endosmosis and 

 capillarity, but also to the buds which by their growth draw up 

 the stem and branches the material necessary for their develop- 

 ment. The buds form leaves, which by affording evaporation, 

 aid in the production of the ascending movement and are a 

 means consequently of manifesting electric effects. 



We know not with exactness the different organs passed 



through by the sap in its evolution. We can say only that m 

 spring it fills the cellules, the fibres, vessels, &:c., and occupies 

 almost entirely the woody substance. The ascending sap, reach- 

 ing the young branches, passes to the surface of the bark in the 

 parenchyma as well as to the leaves ; and when once spread 

 in the green part, it is in direct connection with the atmospheric 

 air, separated from it only by a thin membrane through which 

 respiration is going on. The sap, which is thus intimately modi- 

 fied, becomes less aqueous through evaporation of a part of its 

 water. Carbonic acid gas is decomposed, carbon is assimilated 

 and oxygen exhaled. The color of the leaves and young bark 

 shov/s that considerable changes are going on in the sap. Does 

 this sap, newly elaborated, redescend through the bark, depositing 

 along its passage material for the formation of tissues? Some 

 physiologists still doubt on this point. But the experiments of 



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