PROTECTION OF THE WOODLOT 127 



root. Usually rot starts in a tree as the result of the breaking 

 of the bark on the trunk by grazing animals, by accident or 

 because the inner living bark has been killed by fire or other 

 causes. 



While most fungi grow on the stem and limbs of trees 

 some attack the leaves, others the living bark and others the 

 roots. Some fungi attack only the heartwood, in which case 

 the trunk may become hollow. Since the heartwood has 

 nothing to do with the life process of the tree, the wood being 

 dead, heart rot does not often kill a tree. Trees are often 

 seen growing vigorously with a hollow trunk. Heart rot de- 

 stroys the value of the tree for lumber or other useful pur- 

 pose and so weakens the tree that it is liable to be broken off 

 by a heavy wind. Some fungi attack the sapwood and the 

 cambium, the living layer of the tree. These fungi are most 

 dangerous to the life of trees and soon bring about their 

 death. The chestnut bark disease, which threatens the destruc- 

 tion of all chestnut trees, is of this character. It enters the 

 bark through a wound or even through the lenticles of the 

 bark. It spreads out and develops in the cambium layer, 

 forming a spot that gradually grows larger and larger until 

 the tree is girdled and killed. From the brown patches which 

 it forms on the surface of the bark the spores are spread. 

 The recently imported white pine blister rust is of much the 

 same character. 



Little can be done when trees are attacked by fungi, 

 especially in a large woodlot. Because the disease is in- 

 side the bark, spraying will have no effect as it will not 

 reach the disease. Injections of so-called remedies, or boring 

 holes in a tree and filling with medicine or chemicals of dif- 

 ferent kinds will be of little or no value. The bark on trees 

 in the woodlot should be kept intact. Wounds caused by 

 pruning off branches or otherwise should be painted with a 

 good paint or tar to prevent the spores or seeds of the fungi 

 entering the wood. Fire that kills the inner bark at the base 



