Chestnut Blight in the Southern Appalachians 3 
In chestnut stands where blight has been established for a number 
of years the effect of the disease is so striking as to be evident to 
the most casual observer (Pls. V, VI, and VII). Dying limbs with 
attached browned leaves and burs seem scorched by fire. Branches 
and trunks stand dead. Sprouts grow from the bases of blight- 
killed trees. In turn, they too become infected. Insects and sap 
rots attacking the dead trees cause the bark to peel and add to the 
somberness of the picture. 
When the bark is peeled back from a canker the infected part is 
typically found to contain numerous flattened layers of branching 
mycelium known as fans (Pl. VIII). Their presence is one of the 
best diagnostic symptoms of chestnut blight. Specimens should be 
examined for them when any doubt exists as to whether or not a 
diseased condition is due to blight. 
This test is especially valuable in distinguishing between injury 
caused by blight and that due to root rot, for the latter is the 
disease with which chestnut blight is most often confused. Root rot 
is general in southern chestnut at the lower elevations. Unlike 
the recently introduced blight, it is of long standing. Its prevalence 
accounts in part for the recession of chestnut, which is known to 
have been taking place during the past 75 years. In advanced 
stages root rot occasionally kills the entire tree at once, but more 
often produces the bare top branches known as a staghead. Early 
stages of root rot are easily confused with the blight, especially dur- 
ing drought. Viewed from a distance the symptoms of this stage 
of the disease differ from those produced by blight only in being 
less sharply confined to particular limbs and in the foliage being 
more yellow in appearance. Closer inspection should show no 
cankers with their characteristic fans if the injury is due to root 
rot. Chestnut blight does not attack roots which are covered by 
soil. 
CAUSAL ORGANISM 
The fungus Endothia parasitica (Murr.) A. and A. growing 
within the bark and outermost wood layers of the American chest- 
nut (Castanea dentata Borkh.) causes the disease known as chest- 
nut blight. The vegetative part of the fungus, which is made up 
of very numerous closely appressed threadlike strands, is called the 
“mycelium.” It grows through the bark, pushing out and extend- 
ing much as the roots of higher plants force themselves into soil. 
As the fungus penetrates, it brings about the death of the invaded 
bark. The mycelium within this dead area is buff colored, but 
where it extends into the living bark at the margin of the lesion it is 
often white. The term “fans” has been applied as descriptive of 
these thin spreading plates of fungous growth. 
When well established the fungus fruits. The reproductive bodies 
formed, corresponding to the seeds of higher plants, are known as 
spores. Two types of spores are produced by the chestnut-blight 
fungus. Both kinds arise from pustules, which in dry weather 
resemble orange or red-brown pinheads dotted over the surface of 
the cankers (Pl. TX, A). ; ” 
During damp weather certain pustules produce tiny yellow, coiling 
hairlike tendrils called “spore horns” (Pl. X), which are com- 
