1916 Hurd; on Growth of Nereocystis 193 



the discharge of fresh water from rivers, but a few ascend tidal rivers to a 

 slight extend. Rigg (25) found that so far as the kelps near the mouth 

 of the river Elwha are concerned, they do not grow in water which has 

 not the normal salinity, but he recognizes other factors which may ex- 

 plain their absence at the mouth of the river. Osterhaut (20) questions 

 salinity as an explanation of the distribution of algae near the mouths of 

 rivers, since he has found that they are not very sensitive to fresh water. 

 He notes the red, brown, green, and blue-green algae growing on vessels 

 plying between San Francisco and inland river points, and thus daily sub- 

 jected to the extremes of fresh and salt water. In another paper (21) 

 he reports that algae grew a month in his laboratory in distilled water 

 into which they had been transferred directly from salt water. Other 

 algae grew as long in saturated as in normal salt water. Brown (2) 

 found that Enteromorpha intestinalis can live in fresh water, but that 

 Prionitis, Rhodomela, Fucus, Nereocystis, Desmarestia, Laminaria and 

 Cymathaere die very quickly. Cowles (5) mentions the ability of algae to 

 adapt themselves to media of different strengths, noting specially the "ac- 

 commodation" of Mougeotia. 



The writer's experiments indicate that young Nereocystis plants are 

 very tolerant of fresh water if the concentration of sea water be reduced 

 very gradually. Kelps varying in length from 3 to 14 cm. were fastened 

 to stones by their holdfasts and placed in a tub which was set inside an- 

 other a little larger into which water piped directly from the Sound was 

 kept running continually. This cooling bath kept the temperature of the 

 water within 2° C. of that of the sea water. A wheel attached to a water 

 motor and arranged so as to revolve in the tub around a vertical axis kept 

 the water constantly in motion. The experiment was started on July 9, 

 with the water 100 per cent salt; i. e., natural sea-water. Every 24 hours 

 the tub was entirely emptied and the salinity of the water decreased by 

 Z.5 per cent of boiled fresh water. By July 22 when the water was 30 

 per cent fresh, the kelps had all grown from .3 to .9 cm., depending on 

 their original length. Not until the water became 55 per cent fresh on 

 August 3 did any of the kelps show signs of dying. They all died when 

 the percentage of fresh water reached 60 per cent. However this limit 

 is not considered conclusive because the fresh water used had an abnor- 

 mally high organic content so that it often made the water in the tub ap- 

 pear quite brown. The experiment shows that young kelps are able to 

 adapt themselves to a considerable change in salinity. To make this ad- 

 justment more evident, a young kelp was taken from its natural environ- 

 ment and placed directly in the tub containing water which was 60 per 

 cent fresh. At the end of twenty-four hours it was quite soft, and there 



