6 Nebraska Agricultural Exp. Station, Research Bui. 12 
destructive in the region known as the Middle West, — Illinois, 
Indiana, Ohio, Iowa, Missouri, Kansas, and Nebraska. 
Practically every orchard in the State has more or less 
infection. The extent of infection and amount of damage 
varies, as will be shown later, with the varieties of apples, soil 
conditions, amount of precipitation, and general weather con- 
ditions. 
Owing to the fact that the fungus is a wound parasite and 
since the disease may exist in a tree for several seasons before 
becoming conspicuous or even noticeable, the distribution of 
infections appears very irregular and scattered in an orchard. 
Even when trees become infected at the same time, the dis- 
ease shows externally on some trees long before it can be 
detected on others. After a time the disease becomes notice- 
able on all the infected trees, and finally they are killed. It is a 
common sight in Nebraska to see dead trees here and there 
thruout an orchard, and especially in neglected orchards to 
see whole blocks of dead trees, with here and there a tree 
which still has a few limbs bearing foliage and small apples. 
HISTORY 
The causal fungus was first described in America by 
Schweinitz^" in 1834 under the name Sphaeria discreta. At 
that time it was considered to be a saprophyte and conse- 
quently of no economic importance. 
In 1863 the Tulasne brothers^^ gave an excellent descrip- 
tion of the fungus illustrated by numerous drawings. They re- 
named it Nummularia discreta by which name it is known at 
the present time. That they found it to be a parasite is shown 
by their statement : ''It grows with us during the autumn and 
winter on Sorbus hybrida L. on the thick bark which has re- 
cently died." However, they attached no importance to the 
fungus as the causal organism of the disease. 
It remained for Hasselbring^^ to observe the destructive- 
ness of the disease caused by this fungus. In 1902 he noted 
a cankerous disease very prevalent and doing a great deal of 
damage to orchards in Illinois, which he called Illinois canker. 
He found the disease was caused by the fungus Nummularia 
discreta. In his report he gave a very comprehensive account 
of the symptoms and general appearance of the disease, but 
aside from this added little to the knowledge already furnished 
by Tulasne. 
I'These references are to the bibliography, page 68. 
