CONDUCTIVITY AND PERMEABILITY 217 



If we consider the behavior of the current from this 

 point of view, it is evident that in the simplest cases, where 

 the plant is a membrane only one cell thick (as in 

 Porpliyra and Monostroma) and the current passes 

 through this membrane at right angles to its surface, we 

 need consider only a single cell and its adjacent cell wall, 

 as shown in Fig. 93, A. The part of the current which goes 

 through the protoplasm may be designated as Cp. while 

 that which traverses the cell may be called Cw. 



Experiments show that the resistance of the living 

 tissue is much greater than that of tissue which has been 

 carefully killed with all possible precautions to prevent 

 any alteration of the cell wall. 29 We therefore feel con- 

 fident that the conductivity of the living protoplasm is 

 less than that of the cell wall. 



In order to see how the current may distribute itself, 

 let us suppose the protoplasm to be replaced by a wire, 30 

 P, as in Fig. 93, B and the cell wall to be replaced by 



- 



29 0sterhout (1918, C; 1921, D). 



30 We might consider the protoplasm to be replaced by two wires, 

 one of which corresponds to the thin layers of protoplasm which are 

 traversed by the current in a direction at right angles to their planes, 

 the other corresponding to the similar layers of protoplasm in each cell 

 (around the edges of the cell shown in Fig. 93, A) in which the current 

 flows in the plane of the layer. It is evident, however, that these latter 

 may be neglected in our calculations since they occupy such exceedingly 

 small fractions of the cross-section. 



If we neglect these we may say that in traversing a cell the current 

 passes through a thin layer of cell wall and then one of protoplasm (in 

 both cases at right angles to the plane of the layer), then through the 

 cell sap, and finally through a layer of cell wall and one of protoplasm 

 ( at right angles to their planes ) . It is evident that in this case we may 

 neglect the effect of the cell wall and of the cell sap since their resistance 

 is very small in comparison with that of the protoplasm and is in 

 series with it. We may therefore consider the protoplasm to be replaced 

 by a single wire having a resistance equal to that of the two layers 

 of protoplasm which are traversed by the current in a direction at right 

 angles to their planes. 



