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 

 water, the movement of the water is inward in 

 the cell. This would suggest that tliere 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 ai/ainst the cell wall again. 



Fig. II. 



Spirogj'ra before 

 placing in salt solu- 

 tion. 



Fig. 13. 



Spirogyra from salt 



solution into water. 



, Fig. ,,. 

 S]iirog\Ta in 5', salt solution. 



31. Turg-escence. — Were it not for the resistance which the 

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



