Lecture 3 



51 — 



Absorption 



be caused to enter the cells. For this purpose a test 

 ion not already present in the cell was desirable. The 

 bromide ion was found to be well suited to the need. 

 It could be determined with some facility and was not 

 toxic* 



NITELLA 

 (1000 X) 



CELL SAP 



Ca 



Mo 



CI 



;;;; protopla smv.v.* 



CELL WALL 



. n D 



POND WATER 



Na 



.v.: p R oTo p L A s M ::••, 



CELL WALL 



SEA WATER 



Textfigure 8. — Diagrammatic representation of rela- 

 tive concentrations of several ions in the culture medium 

 and in the vacuolar sap of Nitella and Valonia cells. All 

 ions shown (and POaons also) reach a much higher con- 

 centration in the sap of Nitella than in the external solu- 

 tion. In Valonia potassium is concentrated, but not so- 

 diimi, calcium or magnesium. Sea water is primarily 

 a solution of sodium chloride and the cell sap of potassium 

 chloride. 



The experiments with bromide and some in which 

 potassium also was studied showed that the large 

 Nitella cells retained a limited capacity to take in more 

 ions against gradients, but it seemed to be a necessary 

 conclusion that this capacity was dependent on meta- 



*Subsequently the bromide ion has served a valuable pur- 

 pose in many investigations of the accumulation and transport 

 of ions in higher plants. 



