ABSORPTION, DIFFUSION, OSMOSE. 



15 



plasmic membrane would stretch to such an extent that it would 

 be ruptured, and the protoplasm therefore would be killed. If 

 we examine the cells at the ends of the 

 threads of spirogyra we will see in most 

 cases that the cell wall at the free end is 

 arched outward. 

 This is brought 

 about by the press- 



"'v'..-" 1 ' 



From salt solution placed in water. 

 Figs. 14-16. — Osmosis in threads of mucor. 



Before treatment with salt 

 solution. 



ithin -** 

 upon the proto- After J^L wlth 

 plasmic mem- salt solution - 

 brane which itself presses against 

 the cell wall, and causes it to 

 arch outward. This is beauti- 

 fully shown in the case of threads 

 which are recently broken. The cell wall is therefore elastic; 

 it yields to a certain extent to the pressure from within, but a 

 point is soon reached beyond which it will not stretch, and an 

 equilibrium then exists between the pressure from within on the 

 protoplasmic membrane, and the pressure from without by the 

 elastic cell wall. This state of equilibrium in a cell is turges- 

 cence, or such a cell is said to be turgescent, or turgid. 



32. Experiment with beet in salt and sugar solutions. — 

 We may now test the effect of a five per cent salt solution on a 

 portion of the tissues of a beet or carrot. Let us cut several 

 slices of equal size and about 5mm in thickness. Immerse a 

 few slices in water, a few in a five per cent salt solution and a 

 few in a strong sugar solution. It should be first noted that all 

 the slices are quite rigid when an attempt is made to bend them 

 between the fingers. In the course of one or two hours or less,- 



