390 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIKTY. 



years) as 3 feet G iiiclies in girth of stem, we have a very accurate 

 testimony to tlie correctness of Sir Robert Christison's formula 

 as to the early growth and progress of the yew tree — to which 

 reference has been made in another part of this paper, " An increase 

 materially less than this will consequently indicate some unfavour- 

 able circumstance in cultivation, and may direct attention to it in 

 good time. On the other hand, we must be prepared to encounter 

 occasionally exceptional instances of unusually quick growth, and 

 trace its cause. The observations available for the period of yew 

 life after seventy years are fewer and less precise. Observations 

 by Bowman extend the twelve years rate to the age even of 120. 

 He measured eighteen young yews in Gresford Churchyard, near 

 Wrexham, the age of which was ascertained by a parish record of 

 tlie planting of them, and he found that in 120 years they had 

 attained an average diameter of 20 inches, and consequently an 

 average girth of 63 inches. This gives a growth at the rate of an 

 inch of radius of wood in 121 years. For the next century of 

 yew life after the age of 150, De Candolle brings out, from actual 

 observation, an average growth of an inch of radius in 25| years, 

 uniformly for its whole existence. This result indicates very slow 

 growth for a yew only 63 inches in girth ; and at all events, it 

 gives no insight into the rate of the last century of its life." He then 

 gives other measurements and comparisons, showing the subsequent 

 process of growth during succeeding centuries, and sums up his 

 conclusions after such elaborate arguments and data as follows : — 

 " It seems probable that, under circumstances not unfavourable, a 

 healthy yew in this country grows on an average by an inch of 

 radius every twelve years for the first sixty or seventy years, 

 and will attain the girth of 33 inches at the narrowest part of its 

 trunk ; that the same rate of growth may continue to its 

 hundredth year, or even a little later, giving a girth of 4| feet ; 

 that during the second century of life the average rate is reduced 

 to an inch in fifteen years, giving a girth of nearly 8 feet; that 

 during the next three centuries, the rate on an average can scarcely 

 be greater than an inch in twenty-five years, giving a girth of 

 14 feet at the close of the fifth century ; that during the subsequent 

 five centuries, the average rate for which we have few data, will be 

 somewhere between thirty and forty years, say thirty-five, which 

 will increase the girth of trunk to 22 feet at the close of one 

 thousand years. We thus come close upon the girths recorded 

 of many famous English yews of 25, 27, and 28 feet, which 



