The Relation between the Osmotic Pressure of Nereocystis 

 and the Salinity of the Water 



Annie May Hurd 

 Bureau of Plant Industry, U. S. D. A. 



1. INTRODUCTION 



This investigation has to do with the relation between the osmotic 

 pressure of a marine alga as determined by the freezing point method, 

 and the salinity of the sea water. If variations in the salt content of the 

 environment cause corresponding changes in the cell sap concentration, 

 the question then arises as to how these are produced and whether the abil- 

 ity to so adapt itself is necessary to the plant's tolerance of fresh water. 

 Therefore the problem finds its application in the study of the power 

 of algae to adapt themselves to a change in the salinity of their environ- 

 ment. The experimental part of the work was done at the Puget Sound 

 Biological Station at Friday Harbor, Washington, in the summer of 1918. 

 Urevs (1895) has shown by the plasmolytic method that the osmotic pres- 

 sure of certain marine algae can be increased by concentrating the sea 

 water. The present investigation is concerned only with the adaptation 

 to water of lowered salinity. 



The plant chosen for experimentation was Nereocystis luetkeana, 

 the most conspicuous and interesting plant of the Sound waters. Only 

 young plants were used, because they could be easily grown in tubs in 

 the laboratory. Unusual interest was attached to the problem in connec- 

 tion with this particular plant because of published differences of opinion 

 as to whether it could grow in sea water diluted with fresh water from 

 rivers. Preliminary experiments pointed to the fact that it would stand 

 an astonishing amount of fresh water if it was gradually adapted to it 

 but that any sudden change in salinity resulted in sudden death. The 

 formation of the large blisters in such cases when the change was not 

 gradual led to the idea that the extent of its adaptation was limited by 

 its power of osmotic adjustment to the outside concentration. 



Reports differ as to the occurrence of Nereocystis in sea water diluted 

 by fresh water from rivers. Rigg (1915) and Setchell (1912) are led 

 by their observations to believe that it requires water of normal salinity. 

 But Frye (1915) found it growing near Point Couverden in Alaska in 

 water of only 1 .003 specific gravity, which was almost fresh enough to 

 drink. The water from a creek empties there and "the affected kel))s 



(183) 



