I 9 o6] 6 STERH OUT BALANCED SOLUTIONS 129 



Ptilota filicina, Pterosiphonia bipinnata, Iridaea laminarioides, 

 Sarcophyllis pygmaea, Nitophyllum multilobum, Porphyra naiadum, 

 Porphyra perforata, Gelidium sp., Gymnogongrus linearis, Gigartina 

 mammillosa. 2 



If plants of either group be placed in a solution of pure sodium 

 chlorid (isotonic with sea water), they die in a short timer- -This 

 might be attributed to the lack of certain salts which are necessary 

 for their metabolism, rather than to the toxicity of the sodium chlorid. 

 In the case of the plants of Group i there can be no doubt on this 

 point, for these plants live a long time in distilled water. If we add 

 pure sodium chlorid to the distilled water it kills them in a very 

 short time. An inspection of the tables will show that these plants 

 in their behavior toward sodium chlorid and other salts, closely 

 agree with those of Group 2, which can live but a short time in dis- 

 tilled water. Sodium chlorid is certainly toxic to the first group, 

 and there can be little doubt that it is so to the second group as 

 well. 



The plants of the first group were found in a ditch in a salt marsh 

 through which the tide ebbs and flows; there is always a foot or 

 so of water even at low tide. The salt content of the water fluctuates 

 around a mean of approximately 2 . 3 per cent. 



The plants of the second group were collected at the entrance to 

 San Francisco Bay, where the salt content of the water fluctuates 

 about a mean which is probably not far from 2.7 per cent. The 

 only exceptions are Enteromorpha intestinalis and Ectocarpus con- 

 jervoides, which came from wharves in the bay, where the mean salt 

 content is about 2.3 per cent. 



All the plants used in the experiments were transferred from the 

 sea water directly to distilled water. After rinsing in this they were 

 placed in glass dishes, each containing 2oo cc of the solution to be 

 tested. The dishes were then covered with glass plates to exclude 

 dust and check evaporation. Only a small amount of material was 

 placed in each dish. The temperature during the experiments did 

 not vary far from 18 C. 



Artificial sea water was prepared 3 according to VAN 'T HOFF'S 



2 The determinations were kindly made by Professor SETCHELL. 



3 The water used was distilled in glass only and the first part of the distillate 

 rejected. The purity of each salt was carefully tested before using. 



