iqi2] OSTERHOUT— PLANTS AND SODIUM 535 



Ulva were cut into strips and placed in the solutions. In sea water 

 and in artificial sea water the cells along the cut edges grew and 

 divided repeatedly, but this did not occur in any of the solutions 

 which lacked sodium (figs. 1 and 2). 



In view of these results we may conclude that for the plants 

 studied sodium is as necessary as for animals. That its function 

 is not merely to maintain osmotic pressure is evident from the fact 

 that if sodium chloride be replaced by an osmotically equivalent 

 amount of cane sugar the plants quickly die. That sodium is 



1 



2 



Figs, i and 2. — Fig. 1, portion of a frond of Ulva cut along one edge for experi- 

 ments on regeneration; fig. 2, regeneration along the cut edge of a frond of Ulva; the 

 newly formed cells are dotted; this regeneration takes place only in solutions contain- 

 ing sodium. 



needed to antagonize the toxic action of the other salts in the solu- 

 tion is clear from these and previous experiments. 2 Whether sodium 

 is needed for nutrient purposes must be decided by further experi- 

 ments. 



Since this investigation was begun, papers by Richter 3 have 

 appeared in which he states that sodium is necessary for the nutri- 

 tion of certain marine diatoms but not for that of other marine 

 algae. Aside from diatoms his experiments seem to have been 

 confined to a single unicellular alga. Many unicellular forms are 

 so exceptional in their behavior that it would be unwise to draw 

 general conclusions from experiments conducted on them alone. 

 Richter states that while they grow in the absence of NaCl, they 



2 OSTERHOUT, BOT. GAZ. 42:127. 1906. 



3 Richter, Sitzumzsb. Kais. Akad. Wien 118:1337. 1900. 



