Ill] MENSURATION AND INCREMENT 17 



method of representing graphically the whole life-history of the 

 tree's growth in height, radius, and volume. It is only used for 

 purposes of scientific investigation. 



In order to make a stem-analysis, the tree is cut up into a 

 number of sections of, say, 10 feet in length ; each section is then 

 sawn across the middle, and the number of concentric rings 

 exposed at each cross-section is successively counted and re- 

 corded. 



From this record a table is prepared showing the number of 

 years that it took the tree to grow to the height of 5, 15, 25, etc., 

 feet, up to its present total height. These results are plotted in 

 such a way as to represent graphically a longitudinal section of 

 the tree. A vertical line represents the axis of the tree, with the 

 heights of the successive cross-sections marked on it, and also 

 the heights which the tree had reached at successive periods of 

 its life. 



Then at each cross-section the total number of annual rings 

 is counted, and each ten years' growth in radius, working back- 

 wards towards the centre of the tree, is accurately measured in 

 inches to two places of decimals, and a table is made of these 

 measurements at each cross-section. These radii corresponding 

 to successive ages are then plotted on a series of horizontal axes 

 corresponding to the successive heights of the various cross- 

 sections up to the top of the tree, and the points thus obtained 

 are connected by lines which represent the stem curves during 

 the life of the tree. A calculation can now be made of the volume 

 of the tree at each decennial period, and a series of tables is 

 prepared, giving the volume of each section at each age. 



The periodic increment in cubic feet for every ten years is 

 thus known, and a curve can be plotted, with cubic feet repre- 

 sented by the vertical axis, and age by the horizontal axis, 

 showing the volume all through the life-time of the tree. 



15. Increment of standing trees. 



In the case in which the cubic contents of a certain tree-crop 

 had been accurately measured n years ago, and were found to 

 be V, while the present volume of the same crop is now V, the 



V-v 

 average annual increment will be , and the mean volume of 



J. F. 2 



