274 TRANSACTIOXS OF ROYAL SCOTTISH ARBORICULTLRAL SOCIETY. 



Xo. 2. — Sample Douglas Fir. Measured 1903. 



If the volume per acre be deduced from the equation- 

 Volume per acre Sectional area per acre 

 Volume of sample tree Sectional area of sample tree 



295 X 50-25 

 we tcet, volume per acre = - — ^ , ^_ " =11,171 cubic feet. 



Seeing that this wa.s the method adopted by Dr Scblich, we 

 may accept the last result for purposes of comparison. Deduct- 

 ing the volume per acre in 1888 (3738 cubic feet) from the 

 volume in 1903 (11,171 cubic feet), we get the almost incredible 

 result that 7433 cubic feet of wood have been added per acre 

 during the past fifteen years, an average increase during that 

 period of 495 cubic feet per acre per annum. When, however, 

 it is seen that even the smaller of the two sample trees contains 

 about three times as much timber as the sample tree of 1888, 

 and bearing in mind the fact that no trees have been removed 

 since that year, the result becomes more easy of credence. 



Dining the same period the average height has increased from 

 60 to 83 feet, the point of 3 inches diameter being reached at 

 48 feet in 1888 and 75 feet in 1903. 



Taking the age of tlie wood (forty -seven years) from the time 



