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BOTANICAL GAZETTE 



[APRIL 



i 



net resistance), so that we need consider only the resistance of the 

 protoplasm, of the cell walls imbibed with sea water, and of the 

 capillary films of sea water between the disks. 



When the net resistance is 1200 ohms, we find that on killing 

 the tissue the resistance drops to about 100 ohms. Since this 

 represents the resistance of the cell walls and of the sea water 

 plus the resistance of the dead protoplasm, it is evident that the 

 resistance of the cell walls and of the sea water together must be 

 less than 100 ohms. So far as can be judged from microscopic 

 measurements, the fraction of the cross-section of the conducting 

 column occupied by the cell walls is less than half, and it is prob- 

 able that when the net resistance is 1000 ohms, not more than 50 



* * 



ohms are due to cell walls and to the sea water adhering to the 

 tissues. 



It is evident, therefore, that if the resistance of the living 

 protoplasm had a temperature coefficient of 2, the temperature 

 coefficient of the total resistance would be only a little less than 2. 



We may conclude, therefore, that the temperature coefficient of 

 permeability is not far above 1.33. This indicates that permea- 

 bility is not chemical in nature, although it is not absolute proof, 

 as some chemical reactions have low temperature coefficients. 



It would seem, therefore, that we cannot accept the idea that 

 permeability is chemical in nature without much more conclusive 

 evidence than we possess at present. 



Laboratory of Plant Physiology 



Harvard University 



8 



8 The problem is complicated by the arrangement of the protoplasmic masses 







