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On Electricity in Plants^ and on Vegeto-ferrestrial Currents. 87 



Biot tend to prove the circular movement of the sap. On exam- 

 ining the optical properties of the ascending and parenchymatous 

 sap of the maple, he observed that the first caused the plane of 

 polarization to turn to the right and the second to the left, whilst 

 the two saps of the birch acted the reverse- These experi- 

 ments which according to Biot establish a reciprocal dependence 

 between the two saps, are supposed to demonstrate their circula- 

 ting movement. It is certain at least that the parenchymatous 

 sap differs from the ascending sap. 

 * I , ^he anatomical and physiological details just given were re- 



quired for interpreting certain electrical eifects produced in the 

 different phases of the movement of the sap, effects of interest to 

 meteorology as well as to vegetable physiology. 



The following, are the experiments. Suppose now a stem of 

 a young poplar (when in sap) has been laid open by a transverse 

 section, so as to show distinctly all the concentric layers of which 

 It consists. If the extremities of two platinum needles without 

 polarity, covered or not with a layer of distilled water and in 

 connection with a multiplier, be introduced simuhaneously, the 

 one in the pith and the other in one of the layers of the wood or 

 cortical system, the needle deviates 5, 10, 15 degrees or even more, 

 according to the sensibility of the apparatus, the sappy state of 

 the plant, and the nature of the envelop in which the second 

 needle is placed. The direction of the deviation, which is inva- 

 nable, indicates that the pith furnishes positive electricity to the 

 needle in contact with it, and the outer envelop negative electri- 

 city to the other needle ; there is then a current from the exterior 

 to the interior. 



^ The magnetic needle after some oscillations takes an equilib- 

 niim which is not fixed, the deviation diminishing by degrees 

 Without ever reaching zero. This diminution in the intensity of 

 the current is due to the polarity acquired by the platinum 

 needles, which produces a current inverse to the former and de- 

 stroys its action. The primitive current is the more intense, 

 J other things equal, the nearer the insertion of the outer needle is 



to the epidermis and consequentlv to the green part of the pa- 

 renchyma, i J o r 



On drawing out the first needle from the pith, and inserting it 

 at different points, approximating towards the surface, the cur- 

 rents are similar in direction but of diminishing intensity; and 

 this goes on until the needle is placed in the cambium between 

 tne wood and the bark, when the current changes in direction 

 and becomes more intense, 



On raising a piece of bark, from which the epidermis is easily 

 removed, and applying a plate of platinum to each surface, both 

 ^fing connected with a multiplier, effects of great intensity are 

 oDtamed. With the bark of alder in full sap, the deviations are 



