19"] OSTERHOUT— PLANTS AND SODIUM 533 



that Phyllospadix after being transferred directly to it from 

 sea water lived for 47 days. 



All the solutions were made neutral to phenolphthalein be 

 being used. The 



ma 



light and kept covered to exclude dust. 



The average temperature in experiments with the Pacifig 

 species was about 20 C. and was not subject to much fluctuation. 

 In the experiments on the Atlantic coast the jars containing the 

 plants were partly submerged in running water during the entire 

 period of the experiment, and the temperature did not vary far 

 from 20 C. 



It is very important to avoid an excessive amount of light. 

 The optimum must be determined in each case by experiment, but 

 is usually less for algae than for flowering plants. 



The plants lived much longer in sea water (whether natural or 

 artificial) than in any solution in which the sodium of the sea water 

 was replaced by some other substance. The best substitutes for 

 Na are Ca, Mg, and K. The accompanying table shows the length 

 of life of the plants in solutions made up with these substitutes. 

 It is evident that we cannot say that one of these substitutes is 

 better than another unless we also specify what plant is being 

 experimented on. With one plant Ca fills the place of Na better 

 than anything else, while with another K proves better; with still 

 another Mg is better; and in still other cases combinations (for 

 example, Mg-fCa or K+Ca) are advantageous. 



Great diversity was observed among the different species in 

 respect to their behavior toward the other substances which were 

 employed as substitutes for NaCl. To Phyllospadix the substitu- 

 tion of Li in place of Na is much more injurious than that of Rb, 

 but just the opposite is true of Ulva, while the other plants seem 

 to be injured about as much by Li as by Rb. Similar diversities 

 are found in the behavior of the plants toward the other salts. 

 These facts are important in so far as they give us a clue to the 

 specific action of salts in life processes; this subject will receive 

 further discussion in a subsequent paper. 



All the different plants agree in showing that the replacement 

 of Na by Ca, Mg, or K, all of which are present in considerable quan- 



