48 PRESENT STATUS OF CHESTNUT BARK DISEASE. 
In damp weather or in damp situations the spores are extruded in 
the form of long irregular “horns,” or strings, at first greenish to 
bright yellow in color, becoming darker with age. Plate IV, figure 3, 
shows a part of a branch of a diseased chestnut tree magnified 33 
diameters. In this illustration the typical appearance of the pustules 
in damp weather and the projection of the spores of the fungus in 
the form of “horns,” or threads, are shown. These threads may be 
especially conspicuous near the edges of diseased areas. If the spot 
is on the trunk or a large limb with very thick bark there is no 
obvious change in the appearance of the bark itself, but the pustules 
of the fungus show in the cracks of the bark and, on account of the 
destruction of the layers beneath, the bark often sounds hollow when 
tapped. A patch usually grows fast enough to girdle the branch or 
trunk that it is on during the firs. summer. 
The damage may not be immediately apparent, since the water 
supply from the roots continues to pass up through the compara- 
tively uninjured wood to the leaves, but when in the following spring 
the new leaves are put out they are usually stunted and soon wither. 
The appearance of such trees is very characteristic. Plate IV, figure 
1, shows large chestnut trees killed by the bark disease. In this illus- 
tration the trees to the left show the characteristic stunted foliage, 
which indicates that they were girdled during the previous year, 
while the tree on the right having no foliage was presumably girdled 
by the fungus at least two summers before the photograph reproduced 
was taken. Plate IV, figure 2, shows an orchard tree with recently 
girdled branches. Nothing else except an actual mechanical injury— 
breaking off of trunk or limb—produces such an effect as is shown in 
these illustrations. The imperfectly developed leaves often persist on 
the dead branches throughout the summer. 
The great damage which the disease has done thus becomes most 
apparent in the last week of May or the first week in June, giving 
rise to the false but common idea that the fungus does its work at 
this time of the year, when in reality the harm is done during the 
previous summer. If the first attack is on the trunk, of course the 
entire tree dies. If, on the other hand, the small branches are first 
involved, the tree may live for several years. 
It is very easy for a person not familiar with fungi to confuse this 
parasite with various other fungi which occur commonly on the dead 
wood of chestnuts and other trees, such as species belonging to the 
genera Calocera, Cytospora, and Cytosporina. The superficial re- 
semblance 1s sometimes very strong, but a microscopical examination 
instantly reveals the true nature of the organism in question. On 
account of this common confusion no dependable diagnosis of the 
bark disease can bé made in a new locality without a microscopical 
examination of specimens by an expert. 
141—v 
