SCIENCE PRIMERS. 



[in. 



plants, but, as already pointed out, this process is also 

 often effected by bulbs that separate themselves (tiger- 

 lily) ; or by the budding of underground bulbs (onion) ; 

 or by tubers covered with buds (potato). 



III. THE TISSUES OF PLANTS. 



5. The substance or material of which a plant con- 

 sists is called its tissue ; and there are several kinds 

 of tissue. Their nature cannot be made out without 

 a microscope ; but as a low power will show the 

 most important of them, these should be learned at 

 once. 



6. The chief is cellular tissue (parenchyma), 



FIG. i Cellular tissue of rounded 

 cells, many times the real size. 



FIG. 2. Cellular tissue of rather 

 long cells, many times the real size. 



which forms the principal substance of most plants. 

 It consists of minute oval sacs, called cells, crowded 

 together and often becoming angular by pressure 

 (Figs i and 2). Orange-pulp is an example of cells 

 loosely packed together ; cork and elder pith of cells 

 crowded together which have always been cohe- 

 rent by their sides. The walls of the sac consist 



