[ 41 ] 



CHAPTER YI. 



OF THE WOOD. 



When the bark is removed, we come to the substance 

 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 

 creneral Each of these circular layers is externally 

 most hard and solid. They differ however among 

 themselves in this respect, as well as in their breadth on 

 the whole. It often happens that all the layers are 

 broadest towards one side of the tree, so that their com- 

 mon centre is thrown very much out of the actual cen- 



tre of the trunk. 



The wood owes its strength and tenacity to innumer- 

 able woodv fibres, and consists of various vessels run- 

 ning for the most part longitudinally ; some having a 

 spiral coat, others not. Of these vessels, some m their 

 voungest state convey the sap from the root to the ex- 

 'tremities of the branches and leaves ; others contam the 

 various peculiar or secreted juices ; others perhaps con- 

 tain air. The whole are joined together by the cellular 

 substance already described. 



Linneeus and most writers believe that one of the 

 abovementioned circular layers of wood is formed every 

 year, the hard external part being caused by the cold o 

 winter ; consequently, that the exact age of a sound 

 tree when felled mav be known by counting these rmgs. 



