GEORGE T. SCOTT AND HUGH R. HAYWOOD 37 



meters in diameter, and filled with a clear, watery sap. Within this tluid potas- 

 sium is concentrated to the extent of forty times the concentration in sea water, 

 while sodium is maintained at one third the sea-water level. 



The green plant cell offers a further advantage for studying metabolic factors 

 in cation regulation: the ease of turning on or shutting ofT a normal metabolic 

 process, photosynthesis, by merely illuminating the cells or eliminating light 

 from their environment. Thus, important carbohydrate intermediates are made 

 available to the cell by photosynthetic reduction of carbon dioxide, either for 

 assimilation into stored carbohydrates or for metabolic degradation through 

 the glycolytic cycle. 



METHODS 



Ulva. The methods employed have been described in detail elsewhere (35, 

 37, 38). In brief, samples of Ulva 4 or 5 inches square, previously cut from a 

 single frond, were removed at time intervals, rinsed 30 seconds in isotonic 

 sucrose to remove sea-water contamination and blotted consistently in ab- 

 sorbent tissue to remove the sucrose. Analyses of tissue extracts were accom- 

 plished by flame photometry. As shown in the graphs, samples were removed 

 in triplicate. Values in the tables represent averages of at least three samples 

 each, in which the variation was of the same order of magnitude as in the 

 graphs. In the data to be presented, potassium concentration is expressed as 

 mEq/ioo gm cell water, while sodium values are calculated as mEq/ioo gm 

 dry weight, for reasons to be discussed below. 



Valonia. In order to ensure uniformity of material a large amount of algae 

 was collected at once, the clumps of cells separated and allowed to condition 

 under illumination in the laboratory two or more weeks before use. The experi- 

 ments were carried out in liter beakers containing about 100 cells in 500 ml of 

 sea water. The weight of the cells used varied from 0.15 to 0.3 gm. At various 

 time intervals approximately 10 cells were removed and drained on paper tissue 

 for one minute, placed on cheese cloth which was drawn across a finger bowl, 

 then lowered in distilled water for 10 seconds and again drained on cheese 

 cloth for one minute after which wet weights were recorded. Since samples 

 removed after 20 and 30 seconds are not significantly different in sodium and 

 potassium content from those removed after 5 and 10 seconds, it is unlikely 

 that the distilled-water rinse removes any significant amount of intracellular 

 cation. Preparation for flame photometry followed essentially the same pro- 

 cedure as employed on Ulva. 



RESULTS 



Extracellular Space in Ulva 



In order to obtain valid values for the sodium and potassium concentrations 

 in the cells it is essential to determine what fraction of the electrolytes in the 



