CONDUCTIVITY AND PERMEABILITY 197 



If we attempt to measure the electrical resistance of 

 the protoplasm we must first consider the structure of 

 the tissue. 



Very useful for experiments on tissues are plants 

 which form membranes consisting of a single (Fig. 84) 

 or a double layer (Fig. 85) of cells. In measuring 

 the conductivity of these plants we obtain much the 

 same results as with the more complex tissues of 

 Rliodymenia (Fig. 86) and Laminaria (Fig. 87). We 



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FIG. 86. Cross section of Rhodymenia palmata (dulse). (X 150). 



may therefore conclude that the complexity of structure 

 is not a factor of importance in the interpretation of the 

 results. As a matter of fact in the case of Laminaria the 

 resistance appears to be due chiefly to the rounded cells 

 lying at and below the surface, while the elongated cells 

 which occupy the center of frond have large spaces 

 between them through which the current can easily pass. 



If we consider the structure of the individual cells, 

 we find that in Laminaria (as in the other plants employed 

 in the experiments of the writer) the protoplasm of 



