14 ELECTRO-PHYSIOLOGY CHAP. 



excitable parenchyma of the pulvinus, and it was natural to 

 assume similar bridges between the latter and the cells of the 

 conducting vascular bundles. The effect of local narcosis (ether 

 or chloroform) offered a simple means of deciding the question. 

 Claude Bernard pointed out that the excitability of Mimosa can 

 be temporarily abolished by etherisation. If this is true of the 

 excitable parenchyma of the cushion, it may be conjectured that 

 the excitable cells of the vascular bundles will exhibit the same 

 reaction. The transmission of excitation should be abolished by 

 local narcosis. But the experiments undertaken by Pfeffer (15) 

 pointed to the contrary result. When the central portion of a 

 secondary petiole was treated with chloroform or ether, an injury- 

 stimulus was always a mechanical stimulus sometimes trans- 

 mitted over the narcotised area, Pfeffer therefore concluded " that 

 migration of water is the sole cause of the propagation of a stimulus. 

 This movement of water takes place in the vascular bundles. If 

 excitation is produced by incision of a vascular bundle, so that 

 fluid exudes from the wound, the disturbance of equilibrium in 

 the water distributed in the bundle depends upon abstraction of 

 water. If, on the other hand, excitation is by a mechanical 

 stimulus, a certain, albeit inconsiderable, quantity of fluid passes 

 out of the excited parenchyma of the joint into the vascular 

 bundle ; migration is due to the addition of water " (Pfeffer, 

 I.e. p. 315). In either case Pfeffer refers the propagation of 

 the stimulus from vascular bundle to excitable parenchyma of 

 pulvinus, and vice versa, to the migration of water. The dis- 

 turbance of equilibrium is transmitted to the innermost layers 

 of the parenchyma, immediately adjacent to the bundle, 

 where it acts " as a mechanical stimulus," and discharges the 

 movement. 



Further confirmation of this theory appears in the observa- 

 tions of Haberlandt. He finds that excitation in Mimosa is pro- 

 pagated even over dead tracts of the petiole, destroyed by scalding. 

 If this were entirely the case, it would be conclusive evidence 

 that the conductivity of Mimosa depends not upon a connected 

 system of excitable, or conductive, cells in the vascular 

 bundle, but upon a disturbance of hydrostatic equilibrium due to 

 the injury, and transmitted indifferently over the dead zone of 

 the petiole. Migration of sap would in the same sense lead to 

 conductivity of excitation. 



