PERMEABILITY OF PLANT CELLS 



135 



pressure. It is evident that although the addition of the CaCU 

 lowers the osmotic pressure of the solution, it nevertheless in- 

 creases its plasmolyzing power considerably. Evidently it can 

 do this by hindering the NaCl from penetrating the protoplasm 

 or the two salts may mutually hinder each other from going in. 



It would seem that this experiment furnishes the key to the 

 theory of antagonism, for it is evident that CaCL may protect 

 the cell against the toxic action of NaCl by hindering the NaCl 

 from penetrating the protoplasm and vice versa. 



A striking proof of the correctness of this conclusion is found 

 in the fact that recovery from plasmolysis is very slow in a bal- 

 anced solution of NaCl + CaCl2 as compared with a solution 

 containing only NaCl. With one species of Spirogyra, plas- 

 molyzed in a solution of NaCl containing a little CaCl2 (1 mole- 

 cule of CaCh to 100 molecules of NaCl), the recovery takes 10 

 hours instead of the half hour required when it is in pure NaCl. 

 It is therefore obvious that the penetration of the NaCl is hindered 

 by the presence of CaCl2. 



The fact that recovery occurs in NaCl + CaClo shows that 

 penetration takes place in this mixture. It seems highly proba- 

 ble that not only NaCl but also CaCh penetrates, because in 

 pure solution of CaCL penetration and recovery occurs (though 

 more slowly than in pure solutions of NaCl) and in balanced 

 solutions of NaCl + CaCL the penetration of CaCL into root 

 hairs can be shown by the formation of crystals of calcium oxalate 

 as described above. 



We may therefore suppose that CaCU, entering together with 

 NaCl, may hinder the latter from penetrating rapidly into nuclei, 

 plastids, vacuoles and other structures (even down to those which 

 are ultra microscopic).^ 



The salts must be supposed eventually to penetrate most or all 

 structures in the cell. We may ask whether CaCla protects the 

 protoplast merely by delaying this penetration or whether it 



' In this discussion it seems more convenient to speak of CaCh as protecting 

 the cell against the toxic action of NaCl, but it is probably true in all cases that 

 the antagonism is a mutual one and that the beneficial effect is due to the com- 

 bined action of the antagonistic salts. 



