ACTION OF LIGHT ON VEGETATION. 689 



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. 



Jurgensen 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, 

 the grains of chlorophyll which are carried along by the very watery protoplasm accu- 

 mulate at different spots. A current from thirty elements causes permanent cessation of 

 the movement even if the connection is only momentary. Induced currents act like 

 constant ones ; but the number of induction-shocks which pass through the cells in a 

 unit of time appears to have no considerable influence on the action. 



The changes of form of protoplasm under the influence of a sufficiently strong elec- 

 tric current are, according to the observations of Heidenhain, Briicke, Max Schultze, 

 and Kiihne, similar to those caused by a high temperature near the extreme limit or 

 beyond it. From those of Kiihne it appears to result that protoplasm is a very bad 

 conductor of electricity, and that the excitement caused by a current at particular 

 spots in the protoplasm is not easily transferred to other spots. 



Cohn, Kabsch, and others, state that weak induction-currents act on the sensitive 

 parts of the leaves of Mimosa, the stamens of Berberis, Mahonia, and Centaur ea Scabiosa, 

 and the gynostemium of Stylidium graminifoUiim like concussion or contact, the parts 

 moving as if under the influence of these agencies. According to Kabsch, stronger 

 induction-currents, which permeate the whole plant, destroy the sensitiveness of the 

 gynostemium of Stylidium even for mechanical excitation ; but after half an hour the 

 sensitiveness again returns. The statement of Kabsch is noteworthy that the move- 

 ment of the leaflets of Desmodium gyrans are permanently prevented by stronger in- 

 duction-currents, which however do not kill them. 



end nearest die 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 (p?eony) to the biact or 

 petal ; from the upper to the under surface of the leaf; in the stem diawthorn)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 (^Tropoeolum) from the plant itself to the soil. 

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

 DioTKEa muscipula (see Report of British Association for 1873; also Nature, vol. VIII, p. 479 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 tl.ose of animal muscle and nerve. — Ed.] 



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