1919 Hurdj on Osmosis in Nereocystis 187 



gradually faded as the salinity decreased until the fronds were light brown 

 and somewhat misshapen, so that it did not present a healthy ap- 

 pearance. The extent of the adaptation which the cells of this plant had 

 undergone could be shown very strikingly by placing kelps taken directly 

 from the Sound in any of the sea water dilutions. Large blisters formed 

 on fronds and bulbs within a few hours and the plants became soft and 

 green. At no time were there blisters on the adapted kelps. 



3. DISCUSSION OF RESULTS 



Table 1 shows two very interesting facts. First, that the cells of 

 Nereocystis adjust themselves fairW rapidly to the decreasing concen- 

 tration of the water in which they are growing, the interval between 

 changes to sea water containing 1/28 more fresh water being only 24 

 hours. There is an osmotic adaptation by virtue of which the plants are 

 able to tolerate the fresh water in their environment. That the gradual 

 adaptation brought about by a decrease in the concentration of the cell 

 sap is necessary in this species for the tolerance of fresh water is shown 

 by the blistering, deformity and softening, which result when kelps are 

 plunged suddenly from normal sea water to the lower dilutions. In this 

 Nereocystis differs from those species reported by Osterhout as able to 

 endure sudden extreme changes in salinity. Second, this data shows that 

 nltho the osmotic pressure is steadily lowered in the process of adapta- 

 tion, the cells maintain an average osmotic surplus of 3.62 atmospheres. 

 This osmotic surplus or turgor pressure is the amount by which the pres- 

 sure of the cell sap exceeds that of the water outside. It will be noticed 

 Ihat when the surrounding water was 11/28 fresh, that this surplus took 

 a sudden jump. This may indicate an approach to a limit in the j^ower 

 to lower the osmotic pressure, or a period in the adaptation process in which 

 the adjustment is not so completely made in 24 hours. In either case the 

 pressure of the water would decrease more rapidly than that of the cell 

 sap, giving rise to a higher osmotic surplus. 



This osmotic surplus in Nereocystis of 3.6 atmospheres is low com- 

 pared with that found in Cladophora, Enteromorpha and Chaetomorpha 

 by True (1918). He shows a turgor pressure of 6.6 atmospheres, using 

 the plasmolytic mctliod with cane sugar. Duggar (190(5) also gives data 

 indicating similar turgors in marine algae; viz., Bornetia, Griffithsia and 

 Pleonosporium, but they are reported in terms of salt concentrations caus- 

 ing plasmolysis instead of in atmospheres of pressure. Drevs (1895) 

 found that certain algae maintain a constant osmotic surplus during 

 changes through waters of increasing concentration. It is interesting to 

 compare this relation between sap and sea water concentration in the 

 case of algae with the results of similar work on sea animals. Garry 



