33 



borer,* by meaus of which a cylinder of wood can be extracted from 

 the stem and the width of the rings measured. Taking twice the 

 width of the last five rings and subtracting it from the present diam- 

 eter (at breast height), the diameter the tree had five years ago is 

 nearly enough determined. 



Example : Let the present diameter of a standing tree be 22 J inches at 

 breast height; let the width of the first five rings from the periphery, 

 measured on the cylinder extracted by the Pressler borer, or on the chip 

 of wood cut out, be two eighths of an inch. Multiplying the two eighths 

 by 2 gives one half inch as the diameter increment for the last five 

 years, and subtracting the half inch from 22^, we find that the diameter 

 the tree had five years ago equals 22 inches. In the tables for areas 

 (page 37) we find that the area corresponding to 22 J is 2.76 square feet; 

 that corresponding to 22 inches, 2.64; the difference (2.76-2.64=0.12) 



* Pressler's apparatus (fig. 11) consists of a hollow borer, slightly tapering from 

 the handle toward the point, inserted into a handle; a flat-toothed wedge, which for 

 convenience of measurement is graduated into centimeters; and a cradle, being of 

 a small semicyliudrical piece of tin, used to hold the chip when measuring in order 

 to avoid its break- 

 ing; the handle also 

 is hollow, so as to 

 receive the borer, 

 wedge, and cradle 

 when the instrument 

 is not in use. The 

 borer is screwed in 

 a radial direction 

 into the tree, at right 

 angles to its axis^ to 

 the desired depth, 

 whereby a c y 1 i n - 

 drical column or chip 

 of wood enters the 

 hollow borer; then 

 the wedge is inserted 

 through the hollow 

 borer between the 

 chip and the inner 

 wall of the borer, 

 with its toothed side 

 toward the wood and 

 firmly pressed in. 

 The borer is now 

 screwed backward 

 one or two turns, 



whereby the chip is severed at its base from the tree; a few more forward turns of 

 the borer cause the chip to be pushed back until it can easily be withdrawn by the 

 nse of the wedge and placed into the cradle. In this way a chip of wood is obtained 

 from 2 to 5 inches long, according to the length of the borer. The width of the con- 

 centric rings is then measured. If the rings are not distinct, a smooth surface may 

 be prepared with a sharp knife. 



5107— No. 20 3 



In use. 



Fig. 11.— Pressler's accretion borer. 



