74 AGE OF TREES AND WOODS. 



The business may be facilitated hj smoothing the surface, 

 making a slanting cut, or applying colouring matters (as 

 indigo, alizarine ink, Prussian blue, alcohol coloured with 

 aniline, sulphuric acid, etc.). Such colouring does, however, 

 not always facilitate the counting. 



The number of rings thus counted represents only the age 

 of the tree above the place, where it has been cut. To the 

 number so obtained, the number of years, which the tree took 

 to reach that height, must be added. If absolute accuracy is 

 required, the stool must be split open along the centre and the 

 rings counted to the starting-point. 



In this way, the x>lujsical age of the tree can be ascertained, 

 provided that each concentric ring represents a year's growth. 

 It is, however, by no means certain, whether this is always the 

 case, as temporary interruptions of growth may cause two 

 rings to be formed in one year. (For instance, the destruction 

 of the leaves by insects and the subsequent sending forth 

 of a second crop of leaves, fire running through a wood, or 

 even late frost.) Moreover, there are trees in the tropics, 

 on which the concentric rings do not exist, or cannot be 

 distinguished. 



Another point is, that a distinction must be made between 

 the physical and economic age of a tree. B}' the latter is under- 

 stood the actual growing age, leaving out of consideration any 

 years, during which the tree may have been at a standstill, 

 owing for instance to heavy shade from above. 



2. Determination of the Age oj Whole Woods. 



a. Even-aged Woods. 



If the age of such woods is not known from authentic 

 records, it can be ascertained by determining the age of a tree 

 by one of the methods indicated above. If a tree is felled for 

 the purpose of counting the concentric rings, it is desirable to 

 avoid exceptionally thick trees, as such trees may represent 

 former advance growth. 



