CURRENT PERIODIC GROWTH BASED ON DIAMETER CLASSES 359 



The increment borer (Fig. 74) can be used for measuring radial 

 growth at B.H. This instrument consists of three parts: 



(a) A hollow auger, A, from 4 to 10 inches long, tapering and 

 threaded at one end, and square in cross section at the other end. 



(6) A hollow metal handle, B, with a square opening in the center 

 into which the auger fits when in use. At the ends of this handle are 

 detachable caps. 



(c) A narrow wedge, C, furnished at one end with a flat head, and 

 incised on one side at the other end. 



iWvW/iAl 



TAWvWN 



Fig. 74. — Increment borer, showing construction. 



The wedge and the auger are carried inside the hollow handle when 

 the instrument is not in use. 



To use the instrument one bores into a tree to the desired depth, 

 then inserts the wedge through the auger with the incised de turned 

 inward. The wedge is jammed down, thus holding tightly in place 

 the core of wood within the auger. The handle is then turned sharply 

 to the left, severing the core from the wood. The cylinder of wood is 

 then drawn out, and the rings counted or measured. 



The best type of instrument is made in Sweden, and cores of from 

 6 to 8 inches may be secured by the larger sizes. The instrument is 

 easily taken apart and is convenient to carry. When taken at B.H. 



