64 Nebraska Agricultural Exp. Station, Research Bui. 12 
Of the disinfectants used copper sulphate proved the most 
satisfactory. The efficiencj^ of copper sulphate is no doubt 
due to the fact that the tissues for a short distance beneath 
the surface of the wound retain the copper for a long time. 
Tests made over a year after several applications of copper 
sulphate to the surface of pruning wounds showed the pres- 
ence of copper in considerable quantities. Practically no in- 
jury resulted from the use of copper in this way. 
CONCLUSIONS 
1 Blister canker is very generally distributed. It occurs 
in all fruit growing regions of the United States east of the 
Rocky Mountains and is the most destructive disease of apple 
trees known. 
2 The symptoms of the disease vary with varieties, age 
of trees, available water and soil nutrients and general 
weather conditions. Under certain conditions the injury is 
very similar to that caused by other agencies, such as sun 
scald, winter injury, collar rot, and the so-called arsenical 
poisoning. 
3 Nummularia discreta TuL, is strictly a wound para- 
site. Infections may occur thru wounds in both roots and 
branches. 
4 Infection may be present in a tree for several seasons 
before the disease becomes visible on the outside. 
5 The disease is disseminated by means of ascospores, 
conidia, and infected wood. 
6 Both conidia and ascospores are produced thruout 
the growing season if weather conditions are favorable. Co- 
nidia are usually produced during the same season in which 
the canker first appears and on the surfaces of the same stro- 
mata for many seasons thereafter. Ascospores are produced 
one or more seasons after the conidia first appear. One stroma 
may produce ascospores for several seasons. 
7 Ascospores are much more viable than conidia and for 
this reason offer a better means of disseminating the disease. 
However, conidia also play an important role in spreading the 
disease. 
8 Infection rarely occurs in rapidly growing tissues, but 
takes place readily in inactive xylem tissues. 
9 The fungus does not destroy the cellular structure but 
advances thru the pits in the cell walls. The most rapid prog- 
