AGKS OF TEEMS. 247 



In the case of all exogenous trees — ^those 

 whose additions of cellular matter are made in 

 concentric rings externally to their substance — 

 the scientific test of age is the number of such 

 concentric rings shown in the trunk, as each 

 cylinder of matter annually formed can be distin- 

 guished from the preceding or succeeding cylinders 

 in all cases except those of the first and last. 

 When the outer cylinders of its wood are capable 

 of being counted — by not being broken and 

 confused — the age of the tree corresponds in 

 years with the number of rings shown on a cross 

 section, or a cutting through the trunk in a direc- 

 tion horizontal to the ground. But this process 

 could only be tried by the destruction of the tree, 

 and if that process only of finding out had to be 

 applied, no criterion could be formed of the ages 

 of living trees. But historical notes and coin- 

 cident events have thrown some light on the 

 subject, and experts have, by a knowledge of the 

 whole subject, been able to arrive at some satis- 

 factory results ; so that it may be assumed that 

 the data now to be given are based on a solid 

 foundation, though they are of course only approxi- 



