42 TECHNICAL PROPERTIES OF WOOD. 



the possible spread of the rot, which may, in extreme cases, destroy 

 the entire bole, as shown in Fig. 11. 



Fig. 11. 



Besult of injury along tlie whole of one side of the 

 trwnk and consequent rot (After Boppe). 



Having explained in what forms unsoundness may occur, it is 

 now the place here to explain how to detect internal rot, firstly, in 

 the standing and, secondly, in the fallen tree. 



In the case of a standing tree the crown and upper part of the 

 bole should be searched for decayed stumps of broken-off branches 

 or holes produced by their complete decay. If such be found 

 there is a certainty that the stem of the_ tree is unsound for at least 

 a portion of its length. To assure one's self further, the trunk 

 should be examined at the base for gangrene, and be sounded with 

 the back of an axe. A hollow sound will be a certain indication 

 of hollo wness, a dead soimd of a very advanced stage of rot. A 

 clear ringing sound does not necessarily mean that the trunk is 

 quite sound, for if there is a sufficiently thick shell of sound wood 

 outside, the blow of the axe will return a clear ring. If, in addi- 

 tion to giving out a clear ringing sound, the bole is straight, 

 Symmetrical and without any prominences or excrescences, the 

 presumption is that the tree is sound. In unfavourable soils and 

 localities the trees have a tendency to become hollow and unsound 

 early, and some species exhibit this tendency more than others. 

 Hence in addition to the indications furnished by the examination 

 of each individual tree, the experience derived from previous fel- 

 lings should be utilised. If a tree is soon to be felled, it may be 



