178 



PRIXCIPLKS OF AMERICAN FORESTRY. 



the number 81 in the cohimn of average thrifty trees. Di- 

 vide 81 by 10 (the number of years) and obtain the rate 

 of increase with compound interest, 8.1 per cent. 



PRESSLER'S TARLE. 



InDetermining the Accretion of aFelled Tree the volume 

 is computed from actual measurements. By a few trials 

 the top is cut off where the section contains as many rings 

 as there are years in the period for which the accretion is 

 desired, and the height of the tree at that time measured. 



