26 DISEASES OF DECIDUOUS FOREST TREES. 



stubs, or knot holes. When these fruiting bodies appear it may be 

 taken for granted that the disease has progressed within the trunk in 

 both directions for 2 or 3 feet from the point of infection. 



The disease may affect trees at any time. In its final stages it 

 brings about a complete destruction of the heartwood of the tree, so 

 that it becomes weakened and liable to be broken off by windstorms, 

 thus terminating the existence of the affected tree. Diseased trees 

 may sometimes be recognized by the sound emitted when the trunk 

 is pounded on the outside. While healthy trees give a vibrant sound, 

 trees in the later stages of the disease give a more or less deadsned 

 sound. This is especially true where, owing to the destruction of 

 the decayed wood by insects, holes have been formed. As a general 

 rule, however, the only safe way to recognize a diseased tree is by 

 the presence of the punks or fruiting bodies on the outside of the 

 trunk. 



When cut in two, the trunk of a tree affected with the white heart- 

 rot presents an appearance as shown in Plate II and in Plate III, 

 figure 1, representing both the early and the later stages of the 

 disease. It will be noted that the center of the tree has been trans- 

 formed into a pulpy mass having an irregular outline. This mass is 

 definitely limited on the outside by one or more narrow black layers. 

 In some instances the wood is discolored outside of these black layers. 

 This is more marked in the poplar than in any of the other hosts of 

 the fungus. One of the most characteristic features of the decay of 

 the trunk is that the decayed wood is confined to one large central 

 mass, differing in this respect from the pocket-like destruction brought 

 about by several other wood-destroying fungi, notably Stereum frus- 

 tulosum, which is mentioned later in this paper. 



Trees attacked by the false- tinder fungus rarely become hollow, for 

 after the wood has become thoroughly decayed by the fungus it 

 remains in the interior as a pulpy mass. Where hollows do occur, 

 they are caused by various insects which bore through the decayed 

 wood. 



SUSCEPTIBILITY OF DIFFERENT HOSTS TO THE WHITE HEART-ROT. 



The false-tinder fungus is probably one of the most widely dis- 

 tributed forms of wood-destroying fungi; it occurs on more different 

 species of broadleaf trees than any other similar fungus. Among 

 its hosts are to be found the most important timber trees of the 

 deciduous forests of North America. So far as known to date, the 

 fungus has been found on the following host species: Beech (Fagus 

 atropunicea (Marsh.) Sudworth), aspen (Populus tremuloides Michx.), 

 balm of Gilead (P. halsamifera L.), willow (Salix sp.), sugar maple 

 (Acer saccharum Marsh.), red maple (A. rubrum L.), silver maple (A 

 saccharinum L.), striped maple (A. pennsylvanicum L.), yellow birch 



149 



