86 DISEASES OF ECONOMIC PLANTS 



formation of new cankers, and has established practical 

 control of the disease. 



Illinois canker {Nummularia discreta (Schw.) Tul.), — 

 Attention in America was first called to this as an active 

 parasitic disease in 1902 by Hasselbring/ who attributed 

 to it more serious results than from any other canker 

 disease of Illinois. It has been reported from West Vir- 

 ginia, Missouri, Arkansas, and Nebraska. 



The cankers are at first inconspicuous, unhealthy, dirty 

 brown, usually depressed spots in the bark, sometimes 15 

 cm. in diameter, which enlarge rapidly, particularly length- 

 wise upon the limb, a crack often marking the boundary 

 between dead and sound bark. The interior of the bark 

 of such spots is mottled with dead regions. 



In autumn the sporiferous bodies appear near the borders 

 of the diseased spots, first pushing through cracks in the 

 bark, and exposing pale grayish ochre-colored fungous 

 growths 3-6 mm. in diameter, which, when mature, are 

 slightly saucer- or dish-shaped, and dark in color. These 

 bodies are attached to the dead wood, and remain there 

 even after the bark has fallen away, thus constituting a 

 diagnostic character of absolute reliability, separating this 

 from all other cankers. Discoloration of the heartwood 

 often occurs at a distance of a meter or more from the 

 apparent seat of disease. 



When the cankers become large, injury to the distal 

 parts through interruption of the water supply results. 

 The leaves show symptoms of disease, and the fruit fails 

 to grow to full size. With complete girdling the limb dies. 



Since all infection seems to occur through wounds, pre- 



1 Hasselbring, H., III. Agr. Exp. Sta. Bill. 70, April, 1902. 



