14 



PHYSIOLOGY. 



to move toward the center of the cell. When the salt solution 

 is removed and the thread of spirogyra is again bathed with 

 ^j water, the movement of the water is inward in 

 the cell. This would suggest that there is some 

 substance dissolved in the cell-sap which does not 

 readily filter out through the membrane, but draws 

 on the water outside. It is this which produces 

 the pressure from within and crowds the mem- 

 brane out against the cell wall again. 



/i;.= rJ\ 



Fig. 13- 



Spirogyra from salt 



solution into water. 



Fig. II. 

 Sjiirogyra before 

 placing in salt solu- 

 tion. 



Fig. 12. 

 Spirogyra in 5^ salt solution. 



31. Turgescence.— Were it not for the resistance which the 

 cell wall offers to the pressure from within, the delicate proto- 



