24 



CHAPTER VL 



or THE WOOD. 



W HEN the bark is removed, we come to the sub- 

 stance of the wood, which makes the principal bulk of 

 the trunk or branch of a tree or shrub. When cut 

 across, it is found to consist of numerous concentric 

 layers, very distinct in the Fir, and other European 

 trees in general. Each of these circular layers is ex- 

 ternally most hard and solid. They differ however 

 among themselves in this respect, as well as in their 

 bieadth on the whole. It often happens that all the 

 layers are broadest towards one side of the tree, so that 

 their common centre is thrown very much out of the 

 actual centre of the trunk. 



The wood owes its strength and tenacity to innu- 

 merable woody fibres, and consists of various vessels 

 running for the most part longitudinally ; sonje having 

 a spiral coat, others not. Of these vessels, some in 

 their youngest state convey the sap from the root to 

 the extremities of the branches and leaves ; others 

 contain the various peculiar or secreted juices ; others 

 perhaps contain air. The whole are joined together 

 by the cellular substance already described. 



Linnaeus and most writers believe that one of the 

 abovementioned circular layers of wood is formed every 



