mental unity of the countless members of the vegetable king- 

 dom must disappear when we come to examine their internal 

 structure. 



For, armed with the microscope, botanists have discovered that 

 every vegetable fabric consists simply of an aggregation of cells 

 or closed membranous bags or vesicles, and their unwearied 

 observations have been able to trace the gradual change of this 

 simple elementary form into every variety of tissue, fibre, and 

 vessel, which enters into the organisation of the most compli- 

 cated plants. 



The permeable cell-wall absorbs the nutritious fluids with 

 which it comes into contact, and these, by the chemical processes 

 which are constantly going on in its interior, are changed into 

 new substances, which the cell partly appropriates to its own 

 uses and partly excretes, so as to be able to absorb fresh fluids 

 in their place. The constant succession of these simple physical 

 and chemical actions forms the whole life-history of the indi- 

 vidual cell and consequently of every plant, which, however 

 complicated its structure may appear, is after all but an aggre- 

 gation of cells. 



During the progress of growth the primordial form of the 

 originally globular cell assumes a great diversity of shape ; it 

 extends in length, it branches out, it is flattened by the pressure 

 of its neighbours, or compressed into a many-sided or prismatic 

 figure. 



