THE MOLECULAR FORCES IN PLANTS. 149 



Detmer, Journal f. Landwirthschaft, 27. Jahrgang, p. 380, as also Botan. 

 Zeitung, 1886, No. 30. 



2 See Pfeffer, Untersuchungen a us d. botan. Institut in Tubingen, Bd. 2, pp. 

 '223 and 302 ; and Abhandlungen der mathem.-phys. CL der K. Sticks. Gesell- 

 schuft d. Wiss., Bd. 16. 



59. Turgor and Plasmolysis. 



The substances dissolved in the cell-sap (mineral substances, 

 organic acids, sugars, etc.) osmotically attract water into the in- 

 terior of the cells. As the volume of the cell-sap thus more and 

 more increases, it exerts a pressure on the protoplasm and cell- 

 wall, which, while extensible, are at the same time elastic. The 

 amount of extension in a cell is dependent on the one hand on the 

 magnitude of the osmotic pressure set up inside it, and on the 

 other on the resistance offered by the stretched cell layers (proto- 

 plasm and cell- wall). 1 



We can by suitable apparatus directly represent the essential 

 features of turgor. I use for the purpose glass tubes 80. mm. 

 long and 40 mm. wide. We first close one end of such a tube 

 with a piece of pig's bladder, completely fill the tube with an 

 almost concentrated solution of cane-sugar, and then tie a, piece 

 of bladder over the other end of the tube also. This so-called 

 artificial cell we now immerse in distilled water. The sugar solu- 

 tion osmotically attracts water, so that the cell-contents, the 

 volume of which more and more increases, exert a constantly in- 

 creasing pressure on the end membranes. These bulge outwards y 

 but at the same time themselves exert pressure on the cell con-- 

 tents, owing to their elasticity, and thus a considerable tension, 

 (turgor-tension) is set up in the apparatus between the sugar 

 solution and the pieces of bladder. When the artificial cell is 

 highly turgescent, it is removed from the water. We pierce the 

 membrane at one end of it with a fine needle, and observe that a 

 stream of nuid at once spurts out from the puncture, while at the 

 same time the membranes slacken, A considerable pressure must 

 therefore be present in the cell when it is in a state of turges* 

 cence. 



The following experiment, which can easily be made in lecture; 

 is also very instructive : A small glass is filled with a dilute 

 solution of Potassium ferrocyanide, and a small piece of Copper 

 chloride is dropped into it. The Copper chloride at once surrounds- 



