THE UTILISATION PER CENT. 239 



two years old, grows for r — 2 years during the first rotation, 

 and the increment laid on during these years goes to the old 

 growing stock ; but the increment of the last 2 years of the 

 first rotation is carried over to the second rotation, and so on. 

 If the calculation is carried through on these lines, the following 

 division of the total increment laid on during each rotation will 

 be obtained : — 



At the commencement of the first rotation the normal grow- 

 ing stock is assumed to be present ; it amounts, for an area of 

 100 acres and a rotation of 100 years, to 332,845 cubic feet (see 

 page 228). The total increment laid on during one rotation 

 amounts to 978,100 cubic feet (see page 234). x\s the normal 

 growing stock must again be present at the end of the first 

 rotation, it follows, that the total increment during each rota- 

 tion is divided as follows : — 



Cut away with the old growing stock = 645,255 c' 

 Carried over into the second rotation = 332,845 c' 



Total increment = 978,100 c' 



2. Relation heticeen Noi-mal Yield and Xornial 

 Growing Stock. 



If the normal yield (!',) is divided by the normal growing 

 stock {G,) and the quotient multiplied by 100, the result is 

 called the " utilisation per cent." 



Utilisation per cent. = --/' X 100. 



G,i 



It gives the units of yield for every 100 units of growing 

 stock, just as the increment per cent, gives the units of incre- 

 ment for every 100 units of growing stock. As the increment 

 of a whole series of age gradations is equal to the yield of the 

 same, it follows that — 



Utilisation per cent. = increment per cent, of the whole 

 series of age gradations. 



The utilisation per cent, must fall with the increase of the 

 rotation, just as the increment per cent, has been shown to fall. 



