206 



ANNUAL THICKNESS OF ZONES. 



[BOOK i. 



would appear that the trunk in question, which has a diameter 

 of 5352 lines, would be 1672 years old. This supposition, 

 however, is rather improbable, since perhaps none of the 

 Conifers in the later periods of their growth ever deposit so 

 much as 12'8 lines of wood within four years. If again we 

 assume the annual increase to average only one line, we get 

 5352 rings, and, consequently, that number of years is the 

 age of the tree ; but if we take the mean of these two num- 

 bers, we should arrive at 3512 as the most probable number 

 of years of age, and at an annual addition of ligneous rings 

 of 1'6 lines in thickness, which is sufficiently considerable. 

 The uncertainty, however, of all such computations of age, 

 taken from the measurement of the trunk, without actual 

 count ing of the rings, and the differences which in this 

 respect are caused by climate and soil, may be seen from 

 some examples. 



"De Candolle considers the increase of diameter of the yew, 

 at least in the first 150 years, to be about one line annually. 

 In 120 years, consequently, a tree should be 120 lines, or ten 

 inches thick. But four sections of the trunks of Taxus of 

 various thickness have been measured in the mountains of 

 Bavaria, and their annual rings counted with the following 

 results : 



Thus the thickness of the annual rings amounts to only from 

 one-fifth to nearly half a Bavarian line, a result which, if 

 transferred to the large English specimens mentioned above, 

 would double or treble their age. The thickness of the 

 rings, however, was at the same time so various in the 

 different individuals that in Nos. 1 and 2, thirteen lines 

 of difference in the diameter corresponded to 99 annual 

 rings ; whilst in Nos. 2 and 3, sixty-three lines of difference 



