140 MINUTE STRUCTURE OF THE STEM. 



The largest number of rings yet reported in any case appears 

 to be that given for the great trees of California ; namely, 

 " 2,1 00, with a probability that others considerably exceed this." 1 

 Other higher numbers of rings or estimates of age are, however, 

 given in some works. 2 



399. That it is unsafe to base any calculation of the age of a 

 tree upon its diameter follows from the fact that its growth dur- 

 ing one year differs from that during another (see 400). Even the 

 use of De Candolle's modification of Otto's rule, 3 which is per- 

 haps the best yet given, leads to erroneous results. The method 

 assumes that the number of rings averages nearly the same to 

 any given unit of thickness in the outer as in the inner part of 

 the stem. Having determined the number of rings in an inch 

 just under the bark, this number is multiplied by the radius in 

 order to obtain the whole. For example : Extract from opposite 

 sides of a tree two pieces having a depth of two inches each. 

 Suppose the number of rings in the two-inch piece on one side 

 to be 20, while in the other there are 32, the average per inch 

 will be 13. Deduct twice the thickness of the bark from the 

 whole diameter of the tree, to obtain the diameter of the wood 

 in inches, and multiply one half of the diameter by 13. 



400. The woody rings annually formed in a stem differ con- 

 siderably in size ; a narrow ring being the growth of a cold 



1 S. Watson, in Addendum to Botany of California. 



2 The following estimates cited by De Candolle (Physiologie Vegetale, 

 p. 1007) are believed to range altogether too high : - 



The Linden of Neustadt, in Wiirteniberg, 1147 years. 



The Oak of Bordza (on the Baltic), 710 distinct rings counted and 300 in- 

 distinct rings estimated = 1010 years. (By Otto's rule this would be 1080 

 years.) 



The Yew of Crow-Hurst (Surrey), measured by Evelyn in 1660, 1458 years. 



The Yew of Bra burn (Kent), measured by Evelyn in 1660, and said by him 

 to be superannuated, 2880 years. 



The estimate given by De Candolle, of the age of trees of Adansonia ( Bao- 

 bab) ; namely, 6,000 years, has been shown by Dr. Gray (North American 

 Review, 1844) to be wholly erroneous. 



3 Otto's rule is thus given by De Candolle : Ascertain the diameter at the 

 height of about five feet, and make a notch at the same point on the circular 

 surface, to count a certain number of annual layers which we measure. We 

 then find the annual growth of those trees which have left off growing in height 



by the formula ^-^ ), and of those which continue to grow in height by 



fl> J-J" 



the formula ~ (j ^~^ 2 (/)3 V ; D being the diameter of tree ; V, volume of same ; 



d, thickness of annual layers which have been counted ; n, the number of these 

 layers (Physiologie Vegetale, p. 981 . 



