CARTER: ILLINOIS TREES: THEIR DISEASES 



25 



pies of the affected part. In some cases, suitable samples can be 

 obtained with an extension pruner- These samples can be exam- 

 ined for bark troubles caused by diseases and mechanical injuries 

 and for sapwood discoloration caused by wilt diseases, including 

 Verticillium wilt, Dutch elm disease, and oak wilt. Bark sam- 

 ples from the trunk of a tree can be obtained with a knife, 



Fig. 29. — These cores or borings of wood, from the trunks of different 

 trees, are marked to show the amount of wood produced each year. The 

 core with broad annual rings of wood is from a healthy, fast-growing elm. 

 The core with narrow rings is from an elm that grew slowly for many 

 years and that had numerous branches dying during the last 6 years of 

 growth. The fast-growing elm produced as much wood in 10 years as the 

 slow-growing elm produced in 40 years. During the period when branches 

 were dying on the slow-growing elm, the amount of wood produced in 6 

 years by this tree was equal to the amount of wood produced in 1 year by 

 the fast-growing elm. 



hatchet, ax, or leather punch. Samples adequate for detecting 

 the symptoms of elm phloem necrosis, for example, can be taken 

 with the punch, which does not injure the sampled tree exces- 

 sively. A punch, size 8, 10, 12, or 14, makes a small, round hole 

 that is soon plugged with callus tissue. 



For diagnosis of some tree troubles, it is desirable to obtain 

 samples of the trunk wood. A core or boring of wood (Fig. 29) 

 can be obtained from the trunk of a tree with an increment borer. 

 The amount of wood produced each year by the tree will be indi- 

 cated by the width of each annual wood ring in the core. Exam- 

 ination of the core can determine whether growth has been 

 normal each year, whether it has decreased or increased over a 

 period of years, whether it has stopped abruptly in the current 

 year. A gradual decrease in the amount of wood produced each 



