DUTCH ELM DISEASE IN ILLINOIS 7 



fungus is not obtained by a culture test even though the tree is af- 

 fected by the disease. 



Dutch elm disease is caused by the fungus Ceratocystis ulmi 

 (Buisman) C. Moreau. In Hving trees this fungus grows in the sap- 

 wood, most frequently that of the current season, and causes the 



Fig. 2. — Some affected 

 elms, such as this one, 

 show foliage wilt on most 

 or all of their branches at 

 one time and die rapidly. 



H^/ 



Fig. 3. -In cross-section, the 

 brown streaking caused by 

 Dutch elm disease may appear 

 as a series of dots, as shown 

 here, or as a solid brown band 

 in a single wood ring. 



