184 Pub. Paget Sound Biol. Sta. Vol. 2, No. 45 



are therefore about half the time in almost fresh water and about half 

 the time in almost normal sea water." 



The writer observed that when Nereocystis was plunged directly 

 into fresh water it lost color and became soft in a few hours, the fronds 

 being distorted by numerous blisters formed, evidently, by the rapid in- 

 take of water. But when the salinity of the water on the kelp was grad- 

 ually decreased these effects were not produced and the plants were able 

 to endure a considerable decrease in salinity without showing any bad 

 effects. When a kelp was plunged directly into the same weakened concen- 

 tration of sea water to which plants had gradually been accustomed and 

 in which they were growing in good condition, blisters and other symp- 

 toms of ill health appeared. From this the explanation was offered that 

 the ability of Nereocystis to tolerate fresh water is largely a problem of 

 osmotic adaptation. 



Osterhout (1906, 1906a, 1917) reports some striking instances of 

 the endurance of sudden changes from salt water to fresh water and is 

 led to the conclusion (1917) that "one who is inclined to attribute this 

 remarkable tolerance of fluctuations in salinity to a process of gradual 

 adaptation will meet with manj^ difficulties." However, the following ex- 

 periments show strong evidence that the adaptation of Nereocystis is 

 quite largely a matter of gradual adjustment by a lowering of the con- 

 centration of the cell sap corresponding to the changed osmotic pressure 

 of the sea water. However, the condition of the plants at the end of the 

 process lends color to the view that death in fresh water may occur as the 

 result of a loss of inorganic salts and other substances by diffusion. 



2. METHODS 



The experiment to determine the extent to which the cells of Nereo- 

 cystis can adjust the concentration of their sap and produce equilibrium 

 between the osmotic pressure within and that of the outside sea water 

 consisted essentially of the following: (1) gradually decreasing the 

 salinity of the sea water in the tubs in which the kelps were grown; (2) 

 removing a sufficient number of plants after each change and extracting 

 their juice; (3) getting the osmotic pressure of this juice by means of 

 the depression of the freezing point as obtained with a Beckmann thermom- 

 eter. The apparatus and technique necessary for making these determina- 

 tions is described in any physical chemistry. Helpful details are given in 

 papers reporting investigations involving such determinations (Garry 1904- 

 1905; Harris 1914). 



To subject the plants to different dilutions of sea water they were 

 brought in from the shore with the rocks to which they were attached if 

 possible; if not, they were weighted down by tying a small rock to the 



