86 THE AGE OF TREES. 



Now, to the first or exogenous class belong almost all the trees 

 in temperate regions ; and this class, therefore, has been made the 

 subject of special study by scientific men. 



While it is ascertained beyond a doubt that these trees grow by 

 the addition each year of a new woody layer, it follows as a con- 

 sequence that, by the number of these layers, distinctly marked 

 by the rings which are seen on cutting through the trunk or 

 branch of a tree, we may ascertain, with tolerable correctness, the 

 number of years which have passed since the tree or branch began 

 to grow. 



The cut made through a branch determines the age of that 

 branch, while that made through the ti'unk determines the age of 

 the tree. The irregularities which sometimes occur are so trivial 

 that they need not obstruct our inquiries ; for we may take it as 

 a general rule, that the number of rings or layers indicates the 

 number of years. 



In order that the inspection may lead to true results, not only 

 the number of rings, but the width of each ring, , must be noted. 

 This will give the rate of growth in different seasons, as well as 

 the age of the tree. Let us note the method followed by De 

 Canclolle : " Whenever I meet with a clean cut, off an old tree," 

 says the professor, " which is sufficiently sound to enable me to 

 discover its layers, I place a slip of paper on the branch from 

 the centre to the circumference ; on it I mark, with a pencil or 

 pen, the junction of each zone, noting the side of the pith, of the 

 bark, the name of the tree, its native country, and the particular 

 observations which it has suggested. The collection of these slips, 

 not unlike those in the shops of tailors, gives me an exact appre- 

 ciation of the growth of trees, and the means of comparing them. 

 I am in the practice of marking in a more striking manner the 

 lines which indicate the tens of years, and also of measuring the 

 width from tenth to tenth. My measures being taken from the 

 centre to the circumference, give me the radius. I double the 

 figures, if I require the diameter : I sextuple them, if I require 

 the circumference of the ligneous body." 



De Candolle strongly recommends travellers, and those who 

 live near extensive clearings of wood or dockyards, to prepare 

 such tables as those just described. Where it is impossible to 

 obtain a transverse section of trunks, other modes are recom- 

 mended, i.e., to find out old trees, the date of which is known, 

 and measure their circumference, and by that measure to calculate 



