234 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



Fourthly, the rate of growth indicated in the section up to the 

 year thirty resembles that of the average tree in the Taymount 

 plantation in a striking degree, as the following figures will show: — 



Diameter of average tree at Taymount at 4 feet 6 inches "l 



above the ground, /^^ inches. 



Diameter of thirty years' growth on the section from ) ,i ^^ • i 



■^ •' ° f 11'9 inches. 



America, . . . . . . . . ) 



Assuming, then, that the average tree in the Taymount plantation 

 will show a future development similar to that shown on the above 

 mentioned cross-section, I have endeavoured to forecast the volume 

 of solid wood, or growing stocks (3 inches and upwards in diameter), 

 which an acre of land of the first quality is likely to contain at 

 various periods. 



In order to facilitate my task I shall commence by giving such 

 data for the silver fir, obtained by careful and extensive measure- 

 ments on the Continent. The volume, or cubic contents of a 

 standing tree, is best calculated by the following formula : — 



s X h xj". 



Here s represents the sectional area taken at a convenient height 

 above the ground, usually the height of the chest of a man, or 

 about 4^ feet ; h indicates the height or length of bole ; and / 

 indicates a certain co-efficient called " the form figure." The 

 product oi s X h represents a cylinder with a base equal to that of 

 the tree at 4 feet 6 inches from the ground, and a length equal to 

 the height of the tree, the volume of which is considerably larger 

 than that of the tree, as the latter tapers from the base upwards ; 

 hence /" is a fraction of 1 , and as the product, s x h, is thus reduced 

 by multiplying it withyj the latter is sometimes called the reducing 

 factor. 



During late years a large number of silver fir woods of varying 

 age, from early youth up to muturity, have been carefully measured, 

 arranged in different qualities — best, middling, and inferior — by 

 ascertaining their height, sectional area at height of chest, and their 

 cubic contents ; by dividing with the product of height by sectional 

 area (h x s) into the volume, the form figure has been ascertained. 

 The tables thus constructed can now be applied to the measurement 

 of standing woods without any fellings whatever, by merely 

 measuring the height and sectional area, and by taking the form 

 figures from the tables. 



