426 Martin : Effect of concentrated solutions 



doubled, whereas in uji acetamid the concentration was only 1.33 

 times the normal sap. That, in general, there is an optimum con- 

 centration of the solution which will produce a maximum increase 

 in turgor, and a maximum concentration of the solution beyond 

 which no further increase in turgor will take place, and which 

 may cause the death of the plant, has been shown by the experi- 

 ments of Starge (26). 



Conclusions 



The concentration of cell-sap varies in different plants. It is 

 comparatively weak in Tradcscantia discolor^ but much more con- 

 centrated in Beta vulgaris. 



The limit of concentration necessary to produce plasmolysis 

 varies in different parts and tissues of the plant according to the 

 age of the cell, to the permeability of the protoplast, and to the 

 plasmolyzing substance. With potassium nitrate and urea, the 

 apical cells of Pkilotria w^ere plasmolyzed incipiently, and the 

 degree of plasmolysis gradually increased in the older cells. 

 Glycerine, however, produced strongest plasmolysis in the apical 

 cells* In all cases a stronger concentration of glycerine than of 

 potassium nitrate was required to produce plasmolysis. Acetamid 

 required the strongest concentration of the solutions used. The 

 concentration of urea varied, but was sometimes stronger than that 

 of glycerine. 



The concentration of the cell -sap may be increased by the pen- 

 etration of glycerine, urea, or acetamid. A comparison of the 

 increase in concentration due to the various substances shows that 

 glycerine produces relatively, and sometimes actually, the greatest 

 increase. For, although, in some cases, as in Pkilotria and 

 Spirogyra, urea and acetamid may produce a greater actual 

 increase, this was due to the greater concentration of the plasmo- 

 lyzing solutions. Acetamid cannot increase the concentration of 

 the sap above the concentration of the plasmolyzing solution. 



The duration of the action of the plasmolyzing solution influ- 

 ences the increase in the concentration of the sap. Glycerine and 

 urea, whose action continues several hours, produce a relatively 

 greater increase in the concentration than acetamid, whose action 

 is very quick. The increase in the concentration of the sap of 

 Spirogyra in solutions of glycerine w^as greater after tw^enty-four 

 hours than after five hours. 



