WATER IN PLANT CELLS. 



2 9 



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 pressure from within upon the protoplasmic 

 membrane which itself presses against the cell wall, 

 and causes it to arch outward- This is beautifully 



Fig. 12. 



Spirogyra before 

 placing in salt solu- 

 tion. 



Fig. 14. 



ra from 



salt solution into 

 water. 



Spirogyra 

 lt soluti 



Fig. 13. 

 Spirogyra in 5^ salt solution 



shown in the case of threads which are recently broken. The 

 cell wall is therefore elastic; it yields to a certain extent to the 



