ELECTRICITY. 



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vegetation has at present, like the whole subject, not been investigated scientifically. 

 The destructive discharges of atmospheric electricity which are effected through 

 trees by means of flashes of lightning \ at least show that smaller differences of 

 electrical equilibrium between the air and the earth may also be equalised by means 

 of plants 2. 



The researches on the action of the electric stimulus on the movements of 

 protoplasm and of leaves the motion of which is caused by tension of the tissues 

 have not at present led to any important result from a physiological point of 

 view, although distinguished observers have paid attention to this subject. It can 

 only be said in a general way that very weak constant currents or induction-shocks 

 (for a short time) produce no perceptible effect ; that sufficiently strong electromotive 

 force produces effects on the protoplasm and in the contractile tissues similar to 

 those produced by a high temperature and by mechanical means ; and that finally, 

 when the strength of the current is still further increased, the protoplasm is killed 

 and the motility of the leaves permanently destroyed, but sometimes in the latter 

 case without causing death. 



Jiirgensen allowed the current from a battery of small Grove's elements, the force 

 of which was regulated by a rheochord, to act under the microscope on the tissue of a 

 leaf of Vallisneria spiralis. A constant current from one element produced no perceptible 

 action ; two or four elements caused a retardation of the protoplasmic movement, and 

 when continued for a longer time completely stopped it. When the current was 

 interrupted, the movement, if it had only been retarded, was restored to its original 

 rapidity after the lapse of a short time ; if it had entirely ceased, it was not recom- 

 menced even if the current was at once stopped. When the movement is thus arrested, 



acted as a conductor to electricity. In this way, by destroying the necessary electrical conditions, 

 he thought forests tended to dissipate hail-clouds. Mem. de I'lnst. vol. XXXV. pp. 806, 807.] 



^ [The disruptive effect of lightning upon trees is probably due to the sudden conversion of 

 moisture into steam. See Osborne Reynolds, Proc. Phil. Soc. Manch. 1874, P- ^5-] 



^ [Edwin Smith (Chemical News, Dec. 17, 1869) has detected constant currents of electricity 

 passing in certain directions in plants, as follows : — In a cut piece of leaf-stalk (Rhubarb) from the 

 end nearest the root to the end nearest the blade of the leaf; from the outer side of the leaf-stalk 

 nearest the cuticle to the inner axis ; from the lower end of the flower-stalk (Pseony) to the bract or 

 petal ; from the upper to the under surface of the leaf; in the stem (Hawthorn) from the cambium to 

 the outer cuticle ; in the root (several plants) from the outside to the axis, and from the root-stock 

 towards the apex ; in the hollow stems of monocotyledonous plants (Grass) from the inner to the 

 outer surface ; in the Potato from the centre to the outside ; but in the Lemon, Pear, Gooseberry, 

 and Turnip from the outside to the centre ; in a living plant ( TropcBolum) from the plant itself to the 

 soil. Kunkel {loc. cit.) obtained similar results with the leaves and stems of a number of plants. He 

 found that the direction of the current depended upon the relative moistness of the points in contact 

 with the electrodes, any point being always positive with respect to another which is relatively dry. 

 The currents which are observed appear therefore to be due to the travelling of water in the tissues. 

 Phenomena of the same kind have been observed by Quincke in diaphragms. 



Dr. Burdon-Sanderson has made a remarkable series of observations on the electric currents in 

 DiotKBa muscipula (see Report of British Association for 1873 ; also Nature, vols. VHI, X, and XV, 

 and Proc. Roy. Soc. vol. XXI. p. 495). By the aid of Thomson's galvanometer he has shown that 

 these currents are subject, in all respects in which they have been as yet investigated, to the same 

 laws as those of animal muscle and nerve. Further, The Electrical Disturbance which accompanies 

 the Excitation of the Stigma ofMimulus luteus. Nature, XVI, 1879. See also Munk, Die elektrischen 

 und Bewegungs-Erscheinungen am Blatte der DioncBa imiscipula, Arch. f. Anat. u. Physiol. Du Bois- 

 Reymond, 1876.] 



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