82 HEART-ROT 



cut them down before they are mature than to leave them 

 to be ravaged by disease. 



It is possible to detect a tree which has become actually 

 hollow by tapping it sharply with a stick. The peculiar 

 sound emitted by a hollow tree can generally be recognized. 

 But this only discloses the fact that damage has already 

 been done, and to trace disease in an earlier stage a Pressler 

 borer must be employed. By boring young trees with this 

 instrument the presence of rot can be discovered before 

 the tree has seriously depreciated in value. It is recom- 

 mended that foresters should test their woods every few 

 years by means of such a borer, picking out every tenth 

 tree and boring it a foot or less from the ground to test its 

 soundness. Where diseased trees are found all the trees in 

 the immediate vicinity should also be tested, and those 

 which are attacked should be removed, if possible, root and 

 all. Holes made by the borer must be pegged by pieces of 

 stick, which should be cut off at the level of the bark. 



Heart -rot of the larch is caused by several different 

 fungi, each of which has its own method of attack and causes 

 its peculiar form of destruction in the wood. The most 

 important of these fungi is Fomes annosus, which is de- 

 structive to nearly all species of conifers, and attacks both 

 young and old trees, producing strikingly different results 

 in the two cases. Wood destroyed by this fungus shows 

 small black specks later associated with white patches 

 which ultimately become holes. In this way the wood 

 may become honeycombed and feel soft and spongy, and 

 finally crumble into dust, or, if wet, it may become slimy. 

 In either case it leaves the tree hollow. 



Another very important cause of heart-rot is Polyporus 

 Schweinitzii, which, though it does not make the tree hollow, 

 converts the wood into a darkish cork-coloured substance 

 which is light in weight, smells strongly of turpentine, and 

 when dry crumbles to dust on being lightly rubbed between 

 the fingers. The red-brown fructifications of this fungus 

 may frequently be found growing either on the lower 

 part of trunks themselves, or else on the roots, often at some 



