67 



by the periodical measurement of trees iu ^xperimantal plots 

 established for the purpose. The following remarks apply, 

 therefore, only to those species which form a siagle distinct 

 concentric ring of wood eacli year. 



In the case ot Jelled trees, the required age is found by 

 ■counting the number of concentric rings on the section of 

 the stool or base of the trunk. To ascertain the diametral 

 increase of grovvth, the countings should be made along 

 several radii and the mean should be taken. Where neces- 

 sary the rings in the sap-wood and heartwood, should be 

 separately counted and recorded, and all great extremes should 

 be rejested. Usually, with a view to determine, as is often 

 necessary in order to calculate the possibility in selection- 

 worked forests, the number of years required by trees to pass 

 from one size-class to another, the average number of rings 

 included in the diameter of each size or class is separately 

 recorded. 



For a good many species the age may be very roughly 

 .determined without felling the trees by the use of the little 

 instrument known as Presslers borer, a hollow gi'mlet 

 which, on being screwed into the trunk and then withdrawn, 

 extracts a small cylinder of wood on which the ring-markings 

 can be counted. From two or three such borings, on differ- 

 ent sides of the trunk, the average number of rings per unit 

 of radius can be ascertained. 



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

 with a very sharp-cutting edge (E). 



F 2 



