The Trunk 85 



have a thick bark, are grown among a lot of others the 

 bark is apt to become thin and soft. This principle has 

 to be remembered when plantations are being thinned, 

 as, if this is done too suddenly, trees which have till 



Fig. 43. Trunk of Oak tree with fissured bark. 



then been sheltered by others growing round them will 

 suffer from the sudden exposure to the sun. 



There is one form of bark which is of great commer- 

 cial value. Cork is the inner bark of the cork oak 



