EXOGENOUS WOOD. 



161 



and arriving at the vessels forming a plexis on the surface 

 of every leaf, begins to be changed by the action of the 



FIG. 16. PERPENDICULAR SEC- 

 TION OP EXOGENOUS WOOD 



(ELM). A, the pith, B B, the 

 woody rings, c c, the bark. 



FIG. 17. PERPENDICULAR SECTION OF EX- 

 OGENOUS WOOD (CEDAR), MAGNIFIED. 



FIG. 18. TRANSVERSE SECTION 

 OP EXOGENOUS WOOD (ELM), 

 SHOWING THE GROWTH OF 

 NINE YEARS. 



FIG. 19. TRANSVERSE SECTION OP EX- 

 OGENOUS WOOD (CEDAR) MAGNIFIED, 



SHOWING THE GROWTH OF FIVE YEARS. 



sun's rays, absorbing carbon and giving out oxygen from 

 the carbonic acid always contained in the air. The sap 



M 



