OF VITAL PHENOMENA 103 



therefore, that Na increases, and Ca decreases, the permeability 

 of the cells to ions. The intercellular substance in this and many 

 other seaweeds is of large volume in comparison to the volume 

 of the cells. The ash of Laminaria digitata is 22.4 per cent K 

 and 24 per cent Na. It seems certain that this amount of Na 

 might be contained in the sea water in the intercellular substance 

 and hence the cells be free from it. Evidently the cells store K 

 but the mechanism of this storage is unknown. 



Osterhout (191 5 b) observed that salts of La, Ce, Y, Fe, Al 

 and Th first decrease and then increase the conductivity of 

 Laminaria. 



The experiments of Osterhout suggest an explanation of the 

 function of salts in relation to plants. It was shown by Nageli, 

 Pasteur, Raulin (1870) and others that plants require certain 

 salts that apparently do not enter into the composition of carbo- 

 hydrates, proteins, or fats. Loew showed that these salts are 

 protective rather than nutritive. Thus, he found that either Ca 

 or Mg in excess is toxic, but that these two poisons antagonize 

 the toxicity of one another. The experiments of Osterhout indi- 

 cate that they preserve the normal permeability of the plant cells 

 by their contact with the plasma membrane. To speak more 

 generally, we may say that their presence outside and inside the 

 cells affects the aggregation state of the colloids, and that they 

 affect the plasma membrane, which is probably colloidal. 



Potassium is stored in many plants and probably all of it is 

 needed, while on the contrary, the calcium that is stored in plants 

 in the form of insoluble salts seems to be a waste product. 

 Sodium is needed by some marine plants (Osterhout, 191 2 b). 

 The carbonates, nitrates, phosphates and sulphates are decom- 

 posed by the plant in obtaining the carbon, nitrogen, phosphorus 

 and sulphur for the manufacture of proteids and are in this 

 capacity nutritive, but the chlorides are protective. The car- 

 bonates and phosphates also serve to preserve the hydrogen ion 

 concentration. Before the leaves fall in the autumn the potas- 

 sium is absorbed back into the tree, but the calcium is allowed 

 to remain in the leaf. 



