8 Nebraska Agricultural Exp. Station, Research Bui. 12 
inch in diameter appear all over the affected surface, or in the 
case of large spots where the center has become hard and dry, 
only along the margin of the cankered area. These "blisters" 
are caused by the formation of stromata (masses of spore- 
bearing mycelium) beneath the surface of the bark. Spores 
(conidia) are produced during the latter part of the same sea- 
son or early the next spring. The blisters are ruptured by the 
pressure from beneath, disclosing a pale grayish-tan colored 
mass of mycelium and spores. 
The cankered area increases in size each season as long 
as the branch remains alive. The bark of the older portions 
becomes blackened and rough. The stromata become flat or 
concave on the surface. Continued growth at the edges causes 
them to assume very irregular outlines. Often several blend 
into one, covering an area of nearly an inch in diameter. The 
surfaces of the stromata often appear light gray in color dur- 
ing the early spring, due to the growth of mycelium and the 
production of spores (conidia). Later, especially after the 
bark has been thoroly wetted by rains, the surface of these 
same stromata may appear coal-black due to the presence of 
ascospores which have been formed on the interior and forced 
to the surface. 
With age the cankered bark begins to crack in all direc- 
tions and fall off, leaving irregular patches of dead wood 
exposed. The stromata, however, usually remain firmly at- 
tached to the wood by means of a ring of fungous tissue for a 
considerable period of time after the bark has fallen away. 
If these stromata are removed, irregular dark brown to black 
rings, showing the points of attachment, may be seen in the 
lighter colored wood. 
The point of inoculation often greatly influences the symp- 
toms of the disease. Where entrance is gained thru a large 
wound, cankers are usually formed first at the point of initial 
infection, but if thru a small wound or thru a frost crack in 
the trunk or any of the main branches, the wound usually 
closes and the first cankers may appear in some of the 
branches which have been weakened or wounded. In cases of 
this kind one or more whole limbs often die in one season and 
usually few, if any, stromata are formed on their dead sur- 
faces. When stromata are found in such cases, they are at the 
base of the limb where the fungus can still draw on the living 
tree for food. Where the inoculation takes place near the 
extremity of a branch, the branch is as a rule gradually can- 
kered its entire length and stromata usually dot the whole sur- 
face. In all cases stromata are formed more abundantly 
