VOLUME INCREMENT. 



181 



These tables and illastratioiis justify the following con- 

 clusions: — 



(1.) The current annual increment rises rapidly after tin; 

 first 3^outh is passed, and reaches its maximum, in the 

 case of many species, about the time, when the height 

 growth culminates ; it then falls, and reaches zero at 

 the death of the wood. In the case of other species, the 

 maximum is reached some time after the culmination 

 of the height growth, as in the case of silver fir. 



100 



120 



-20 40 60 SO 



AGE, IN YEARS. 



Fiff. 42. — Diagram showino: the Mean Aumial lucreraeut. 



(2.) The mean annual increment keeps below the current 

 annual increment, until the two become equal ; after 

 that period, the mean annual increment is greater than 

 the current annual increment. 



(3.) The mean annual increment reaches its maximum at 

 the precise moment, when it is equal to the current 

 annual increment. 



(4.) When the mean annual increment culminates, the 

 current annual increment must, naturally, already be 



