Studies on the effect of some concentrated solutions on th 



activity of 



* 



Harriett Marie Martin 



Turgidity, which is often of importance in bringing about 

 rigidity in plant parts, is dependent to a great extent upon the 

 osmotic pressure of the cell-sap, which keeps the cell-wall stretched 

 to its greatest extent. The concentration of the cell-sap, upon 

 which the osmotic pressure depends, varies according to the en- 

 vironment of the cell, and the permeability of the plasma-mem- 

 branes. 



Plasmolysis affords a means of studying the concentration of 

 the cell-sap, and the changes which may be induced by the en- 

 vironment of the cell. If the cell lies in a solution more concen- 

 trated than the cell-sap, the greater osmotic pressure of the ex- 

 ternal solutes will cause a contraction of the protoplast. The 

 protoplast will withdraw from the cell-wall to a greater or less 

 extent, according to the increase or decrease of the difference be- 

 tw^een the external and internal osmotic pressures. It is this 

 withdrawal of the protoplast from the cell-wall which constitutes 

 plasmolysis. 



In dealing with certain substances, glycerine, urea and aceta- 

 mid, to which the plasma-membrane is more or less permeable, 

 and which are considered harmless to the protoplast (Overton 17 

 and 18; Hampe 9; Beyer 2; de Vries 33; Klebs 10; Laurent 

 1 1 ; Meyer 14^), it was desired to ascertain if a stronger concen- 

 tration of other substances would be necessary to bring about 

 plasmolysis, after treatment with glycerine, urea, or acetamid, than 

 under normal conditions. 



Methods and experiments 



In general, the experiments consisted in first determining the 

 concentration of potassium nitrate, glycerine, urea, and acetamid 

 isotonic with the cell-sap, namely such a solution as would just 



* Contribution from the Botanical Department of Cornell University No. 104. 

 Numbers 1-102 are listed in a History of Cornell University, published by Tlie Uni- 

 versity Publishing Society of New York City, 1905. 



; 



415 



