and the Means of ascertaining it. 



335 



TABLE of the Periods of Increase in Diameter of some Exogenous 

 Trees, expressed in lines* 



On an inspection of these figures, we will find, that trees at ad- 

 vanced periods of life continue to form layers which do not yield 

 in thickness to those of a moderate age ; that each species, after 

 increasing rapidly in youth, seems at a certain age to grow at a 

 regular rate ; that, in short, we can give a tolerable explanation 

 of such a difference, by supposing that at an early period, i. e. 

 before fifty or sixty years, the roots and branches of forest-trees 



