DURATION, OF THE LIFE OF PLANTS. 361 



siders their age to be at least equal to the number of lines in their 

 diameter. This average, however, is probably too high for young 

 trees, and too low for old ones. In 1836, Mr. Bowman measured the 

 trunks of eighteen Yews in the churchyard of Gresford, near Wrex- 

 ham, in North Walep, which were planted out in 1726, and found 

 their average diameter to be 20 inches, or 240 lines. Comparing 

 them with the dimensions of other trees whose ages are known, he 

 came to the conclusion, that for Yews of moderate age, and where the 

 circumference is less than 6 feet, at least two lines, or ^ of an inch of 

 their diameter, should be allowed for annual increase, and even three 

 lines or more if growing in favourable circumstances. He states that 

 a Yew in the same churchyard, whose mean diameter is 8 feet 6 inches, 

 or 1224 lines, and whose age, by DecandoUe's method, would be as 

 many years, was in reality 1419 years old. Sections taken from 

 different sides of the trunk contained as follows : — 



, T j> 1 . ■ V ( On the north side 43. 



Average numher of annual nngs per inch, q^ ^^^ ^^^^^ ^.^^ ^ 



counted on the horizontal plane . i r, i-u 4.1, 1 -j ic 

 ■^ [On the south-west side 15. 



giving a general average of 34§ rings in an inch of the diameter. 

 Supposing that this tree, when 150 years old, had a diameter equal to 

 that of the eighteen already mentioned, and among which it grows, 

 and had continued to increase in the same ratio up to 150 years, and 

 also making additional allowance for an intermediate rate of increase 

 between 150 and 250 years, Mr. Bowman arrives at the following 

 result : — At 150 years old, its diameter would be 25 inches; at 246 

 years old, 33 inches, leaving 5 feet 9 inches of the diameter for subse- 

 quent increase, the radius of which, at 34 rings to the inch, would 

 contain 1173 rings, or years of growth; to this add 246, and its 

 present age would be 1419 years. 



Another Yew in Darley churchyard, Derbyshire, is mentioned by 

 Mr. Bowman, in which sections taken from its north and south sides 

 gave 44 annual rings in the inch, so that its radius would contain 286 

 such rings, supposing them to be of equal thickness throughout, but 

 making the same deductions as before, its present age may be esti- 

 mated at about 2006 years. This examination shows the Gresford 

 Yew to be about 200, and that at Darley about 650 years older than 

 DecandoUe's standard of one line per annum of the diameter would 

 indicate, and consequently, that for old trees his average is too low. It 

 also shows that the Darley tree, with a greater diameter than the 

 other of only 1 1 inches, is 587 years older, the excess arising from the 

 extreme thinness of its annual deposits. No precise rule can there- 

 fore be laid down, and actual sections must be resorted to if anything 

 like accuracy be required. 



