334 Prof. De CandoUe (yn the Longevity of Trees, 



an idea of the number of years which have rolled on since the 

 moment at which the portion of the tree where this section was 

 made, commenced to grow. Of course, a cut at the base of a 

 branch gives the age of that branch ; that which is made at the 

 base of the trunk, or at the neck, proves the age of the tree. If, 

 as some maintain, there may occasionally be seen irregularities, 

 it is a very debateable point ; and it may, at least, be affirmed, that 

 possible errors, if there be any, are so rare and so trivial, that 

 one may confidently argue on the hypothesis, that the known 

 number of layers indicates the number of years : of course, 

 whenever we can procure a clean cut of a trunk, this very sim- 

 ple criterion is sufficient to determine the age of the tree. But 

 the inspection of these concentric zones should be made more 

 carefully than it has been hitherto. These zones prove the age 

 by their numbers, but the rate of the tree*'s growth is discovered 

 by the proportion of their thickness. They must not only be 

 counted, but measured. For this object I employ the following 

 plan, which is very simple, whenever I meet with a clean cut of 

 an old tree, 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 particu- 

 lar observations which it has suggested. The collection of these 

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

 appreciation 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 tenths of years, and also of 

 measuring the increase from tenth to tenth. My measures be- 

 ing taken from the centre to the circumference, give me the 

 radius. I double the figures if I require the diameter ; I sex- 

 tuple them if I wish the circumference of the ligneous body. It 

 is almost useless, except in certain cases, to make similar re- 

 searches concerning young trees, because in operating on the 

 oldest trees of each species which can be obtained, we possess 

 the advantage of judging of trees at all the stages of their 

 growth. As it would be inconvenient to publish an engraving 

 of these slips, which are sometimes several feet long, I give an 

 idea of these results by means of the following table : — 



