160 



ELEMENTS OF STRUCTURAL BOTANY. 



Fig. 220 shows some cells from the same rootlet taken 

 ;til] farther back. It is clear that the change observed 

 .11 Fig. 219 has been carried to a still greater extent. 

 In some of these cells the proto- 

 plasm is restricted to the lining 

 of the cell and the nucleus. 



261. It is now to be observed 

 that the protoplasm is the es- 

 sential part of every living cell 

 Through its agency all the vital 

 processes of the plant are carried 

 on. Every cell of every plant 

 at some time or other contains 

 this substance, and when at 

 length it disappears the cells 

 which are deprived of it no 

 ~^ longer take any active pai't in 

 the growth of the plant, but serve 

 merelymechanioal purposes, such 

 as that of support or conduction, 

 and are in that stage of their 

 history filled usually with air or 

 water. The pith of the Elder 

 is made up of such dead cells, 

 as is also the greater part of the 

 wood and bark and older parts 

 Fig. 220. generally of all plants. 



262. The most marked feature of the living protoplasm 

 is its activity. We may observe this property by 



Fi<f. 2-20. — Cella still older ; h, the wall ; *', vacuoles ; p> protoplasm ; fc, 

 nucleus ; xy, swelling of nuQleug Ctvused by water used in prepa,r^tiQn of the 

 jeption, (Sachs.) 



