PERMEABILITY OF PLANT CELLS 



137 



experimental conditions. It is desirable that the amount of 

 space between the cells be constant so that the current which 

 passes between the cells may be a constant fraction (as small as 

 possible) of that which actully traverses the li\dng protoplasm. 

 The current should pass through a large number of thin sheets 

 of living tissue, separated by thin films of solution. The pene- 

 tration of various ions may then be studied by merely changing 

 the solution. 



All these conditions are admirably fulfilled by the common 

 kelps of the Atlantic coast (species of Laminaria). This material 

 was accordingly used throughout the investigations.* 



If the plasma membrane and the cell wall presented no obstacle 

 to the passage of ions we should expect the resistance of a cylinder 

 of living tissue to be practically that of a similar cylinder full 

 of sea water. It was found that a cylinder of living tissue had a 

 resistance of 1100 ohms (all the figures given in this paper refer 

 to readings taken between 18°C. and 18.2°C.) while that of a 

 cylinder of sea water of equal size was 320 ohms. To ascertain 

 whether this excess of resistance was due to living protoplasm or 

 to cell walls the protoplasm was killed by adding sufficient formalin 

 to the sea water to make a 2 % solution. In other experiments 

 the disks were killed by careful drying. In all cases the resist- 

 ance after killing fell to about 320 ohms. These experiments 

 demonstrated in the clearest manner that the ions penetrated 

 less rapidly into li\dng cells than into dead protoplasm or into 

 cell walls. 



Experiments were then made to determine the rate of penetra- 

 tion of various ions. As the treatment was the same in all cases 

 it will suffice to describe a typical experiment dealing with NaCl 

 and CaCl2. 



The material was first tested in sea water and found to have a 

 resistance of 1100 ohms. After remaining four hours in sea 

 water the resistance was unchanged. The material was then 

 transferred to NaCl 0.52 M which had the same temperature as 

 the sea water and the same conductivity (as determined by num- 

 erous careful tests). 



'The method is described in Science N. S. 34: 187, 1911. 



