STRUCTURE.] 



IS VERY VARIABLE. 



207 



corresponded to only 78 rings ; results which harmonise with 

 the average thickness of the rings stated above, only inasmuch 

 as that the individual rings of the same stem differ consider- 

 ably among themselves. Four sections of Pinus sylvestris, 

 taken from very different localities, were estimated in the 

 same way. 



Thus in these four stems the thickness of the annual rings 

 varied between 3- 8 lines and 0'39 lines. At the same time, 

 in Nos. 1 and 2, twenty-two lines of difference in diameter 

 correspond with 173 annual rings, but between Nos. 3 and 4, 

 and No. 2, the proportion is reversed, since in the two latter, 

 a greater diameter corresponds with a less number of rings, 

 for whilst in No. 4, the 84 lines of diameter correspond with 

 56 rings, in No. 2, seventy- two lines give more than three 

 times that number, or 186 rings. 



" Similar anomalies are presented by the Spruce Fir, Larch, 

 and also by Pinus Cembra. These statements, however, 

 suffice to prove that conclusions as to the age and number of 

 annual rings of a tree cannot, at present, be drawn with any, 

 or with only occasional, probability, from the diameter, except 

 in those cases in which the growth has taken place under 

 exactly similar external conditions. The four yew stems 

 were from the Bavarian Alps, and the altitude of the respec- 

 tive localities at which they grew cannot differ more than 

 3000 feet; the thickness of the rings varies among them 

 almost one-third; but in comparison with the instances 

 given by De Candolle, more than the half or even two- 

 thirds. According to this, yews of the same diameter may 

 be 100, 200, or 300 years old. But in the Scotch fir the 

 difference in the thickness of the rings, under great differences 

 of external condition (as between Nos. 1 and 2) amounts 

 to one-ninth ; and under nearly similar circumstances (as 



