'>1D 



Ilurdj on Osmosis in Nereocystis 



189 



5. DEMONSTRATION OF INTERCHANGE OF WATER AND SALTS IN OSMOTIC 



ADAPTATION 



After it was shown that the osmotic pressure of Nereocystis de- 

 creases as the salinity of the water is lowered, the question naturally 

 arose as to how it was brought about. The blisters which form so quickly 

 on fronds and bulb when a plant is plunged suddenly into water containing 

 less salt than does normal sea water, was evidence that it might occur as 

 the result of the intake of fresh water and a consequent dilution of the cell 

 sap. Then, too, it seemed possible that the change to an abnormal salinity 

 might so change the permeability of the cell membrane as to allow a 

 diffusion of salts from the cells out into the water, which loss would cause 

 a decrease in pressure within the cell. Experiments were then under- 

 taken to demonstrate whether either of these or both were responsible 

 for the observed phenomena. 



To determine whether fresh water in the environment causes a loss 

 of salts small plants were placed in 250 cc. volumes of different dilutions 

 each of known chlorine content ; after a plant had remained in each for 

 24 hours the water was again titrated with silver nitrate (n/,0975) for 

 chlorides. In all cases the kelps used were as nearly equal in size as 

 possible. The results of these titrations are tabulated. 



Table 3. Showing the relation hetxveen the salinity of the water and the 

 loss of salts from Nereocystis plants in it 



Sea water 

 dilution in 

 wliicli lielp is 

 left 24 hours 



Undiluted sea 

 water 



3 vol sea water : 

 1 vol. fresh water 



2 vol. sea water : 

 2 vol. fresh water 



1 vol. sea water : 

 8 vol. fresh water 



Fresh water 



Total CI in g. per 



1. in dilution 



after containing 



kelp 24 hrs. 



10.567 



G.559 



3.174 



CI supplied by 

 sea water in the 



dilution in 

 grams per liter 



12.712 



8.475 

 4.237 



0.000 



Excess CI which 



must have come 



from kelp 



0.000 



0.254 



2.092 

 2.322 



3.174 



We conclude from this table that the dilution of sea water with fresli 

 water causes a diffusion of salts out of plants placed in it. This is shown 

 by the fact that the amount of chlorides found in the diluted sea water in 

 which kelp has been left 21 hours is greater than the amount in the water 

 before the kelp was jjlaccd in it, the excess of necessity coming from the 



