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 fee] 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 
Schweinitzit, 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 
