32 Puget Sound Marine Sta. Pub. Vol. 1, No. 6 



upon which Enteromorpha intestinalis was growing. About every third 

 day the water was siphoned off to avoid disturbing the algae and fresh 

 water of the same per cent was added. On the days during which the 

 water was not changed it was aerated by splashing with the hand. 



At the end of five weeks all of the plants were living, but none 

 seemed to be reproducing. The plants in the fresh-water end of the 

 series were larger than those in the salt-water end {Plate 3), but they 

 were not so deeply green. Observations on the waters in the pails showed 

 that the water which was 100 per cent fresh became "milky" sooner than 



100 98 95 90 85 80 75 70 60 50 40 30 20 10 



PLATE 3 



A series of typical plants showing increased growth in the less salty waters. 

 The figures below the plants indicate the per cent of fresh water in the water 

 in which they were groAvn. 



that in the other pails, and a slime gathered on it. It was easier to tell 

 by feeling this water than by looking at the plants in it that it was not 

 in so good a condition bacterially as the others. The pail and the water 

 in it showed better the difference from the others than the algae growing 

 in the pail. It seems probable that Enteromorpha intestinalis does not 

 need salt so much for its own growth as it does to check the growth of 

 bacteria. It would not be at all a surprise if this species would thrive in 

 fresh water as well as in salt water if the bacterial content of the fresh 

 water were kept down in some manner not harmful to the algae. Lack 

 of time prevented experiments along this line. 



At the end of four weeks, to get specimens to examine under the 

 microscope, average plants that were still attached to stones were taken 

 from each pail and laid in order. Thus was secured the series shown 

 in Plate 3. From this series it seems that the algae grow larger in the 

 fresher water than in the saltier water. This seems to imply that salt 



