38 



This instrument (see figure) is a gimlet, consisting of a tube (G) 

 with a very sharp-cutting edge (E) . 



To render the instrument easily portable, the gimlet portion G 

 can be taken off and put into the cylinder CC, which is hollow, 

 and the caps of which unscrew off. 



As the tube is forced into the trunk of a tree, a cylinder of 

 wood is cut out by the tube. On withdrawing the gimlet, the 

 cylinder of wood can be easily pushed out of the tube and the ring- 

 markings on it counted. When the borer does not quite reach 

 the centre of the tree, the age of the remaining portion of the trunk 

 can be estimated with sufficient accuracy. 



If the conditions of the forest have not materially altered since 

 the appearance of the trees experimented upon, the ring-countings 

 will give also the age of individuals of "any girth-class smaller 

 than the class to which those trpes belong. 



2. Determination of the age of felled trees. , 



It is scarcely necessary to say that, under the assumption made 

 at the beginning of this chapter, the required age is accurately 

 determined by counting the number of concentric rings on the 

 section of the stool or trunk.- The remark made in the last para- 

 graph of the preceding article holds good here also. 



5. Determination of the age of entire crops. 



If the crop is regular, its. age is practically the age of the mid- 

 dle class of stems composing it, and. it will hence suffice to deter- 

 mine the age of one of those stems, or, to be on the safe side, of a 

 few of them. 



