(Did the Means of ascertaiidng it. 107 



when wo speak of their germination. We shall succinctly ex- 

 amine the means of determining the age of individual trees of 

 both these classes, and conclude with a few words on vegetables 

 more humble in their appearance, but whose longevity presents 

 some singular ambiguities. 



1. Almost all the trees in temperate, and of course in the 

 most civilized, countries of the globe, belong to the exogenous 

 class ; and its history having therefore been more carefully 

 studied, can supply us with the most valuable information. It 

 is known, however, by means, of the truth of which there can 

 be no doubt, that exogenous trees grow each year by a new 

 woody layer, and that, in consequence, the luiraber of concentric 

 zones which are seen on the transverse or horizontal cut of a 

 trunk, may give an idea of the number of years which ha\e 

 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 a 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 debatable 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 in- 

 dicates the number of years ; of course, whenever we can pro- 

 cure a clean cut of a trunk, this very simple 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 num- 

 bers, 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, v/hich is sufficiently sound to enable me to discover its 

 layeis. I place a slip of paper on the branch from the centre 

 to the circumference ; on it 1 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, rot unlike those in the shops of tailors, gives me an exact 

 appreciation of the growth of trees and tlic 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- 

 hvx 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. Il 

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



