CHAPTER II. 



GENERAL VIEW OF THE STRUCTURAL CHARACTERS OF ANIMAL 



ORGANISMS. 



The parts played in physiology by cells are so many and so 

 important that it is necessary at the very outset to consider their 

 properties somewhat in detail. 



FIG. 1. 



Cells from the root of a plant (X 550).!. Showing youngest cells with thin walls (w), 

 filled with protoplasm and containing nucleus (N)and nucleolus(N'). 2. Older cells with 

 thicker walls with vacuoles and cell sap (s). 3. Shows further diminution of protoplasm 

 and increase in cavity (s) in proportion to the growth of the cell wall (w). 



The demonstration of the cellular structure of plants was first 

 made in 1832 by a distinguished German botanist named Schlie- 



33 



