122 PHYSICAL CHEMISTRY 



contracted it was drawn in at the ends and pushed out at the 

 sides, so that the same area lay between the electrodes, but was 

 now composed of a smaller number of larger cylinders. It may 

 be objected that the surface of the contracted fibers is thrown 

 into waves but this does not affect the problem, because such 

 fibers can be resolved into an infinite number of short cylinders 

 of different sizes placed one on another. If a change in the 

 diameter of all of the fibers does not affect the conductivity, a 

 local variation in the diameter of one fiber does not affect it. 

 It seems that the evidence points to an increase in the permeabil- 

 ity of the muscle on stimulation. 



It was shown by Kunkel (1887) and Burdon-Sanderson 

 (1888) that an action current follows stimulation of the sensitive 

 plant, Dionea, and the same has been found true of a host of 

 plants by A. D. Waller. It seems probable that an action cur- 

 rent (blaze current) follows stimulation of any plant except 

 perhaps most marine plants, as indicated by Waller. 



This increase in permeability may cause movements (in addi- 

 tion to electric phenomena). Pfeffer ("Physiol. Untersuchungen" 

 1 and 2, 1873) studied the movements of plants. The stiffness 

 of a plant is due to the pressure or turgor within its cells, and 

 Pfeffer observed that plant movements are caused by local varia- 

 tions of turgor. Each cell is surrounded by a semipermeable 

 plasma membrane. The osmotic pressure within the cell causes 

 the absorption of water, from the capillary spaces between the 

 cells. When the plant is stimulated certain cells lose their semi- 

 permeability and the cell sap filters out into the intercellular 

 spaces, causing a local shrinkage of the tissue. 



Waller (1904) observed that the conductivity of plants may 

 increase 100 fold (or less) on stimulation, thus giving more evi- 

 dence for permeability increase. He observed the blaze current 

 to last fifteen minutes in some cases, which makes it easier to 

 study conductivity during the stimulated state. 



Whereas the action of the sensitive plant may reach a maxi- 

 mum one second after stimulation, movement does not begin 

 until two and one-half seconds after stimulation. The time re- 

 quired for diffusion together with the mechanical inertia of the 

 parts probably accounts for the delay. 



We may sum up the data on the universality of the bioelectric 



