IV.] 



BOTANY. 



IV. THE 



GROWTH OF CELL-TISSUE, AND 

 NATURE OF THE CELL. 



10. To understand how plants grow, and how such 

 products as sugar, starch, oils, resins, and medicinal 

 substances are formed in them, it is necessary to ex- 

 amine further cellular tissue ; for it is by the addition 

 of cell to cell that plants grow, and by chemical 

 changes taking place within the cell, that the above- 

 named and other substances are formed. 



11. The cell consists of a wall (cell- wall) and its 



FIG. 5. Growing point of stem of stonewort showing formation of new 

 cells by division, many times the real size. 



contents (cell-contents). The cell-wall is a thin (rarely 

 thick) transparent bag of inert or dead matter called 

 cellulose ; it contains when young a viscid granular 

 substance endowed with life and sometimes exhibiting 

 motion, called protoplasm. Cellulose is composed 



