August, 1945 



Carter: Wetwood of Elms 



417 



I 



Fig. 16. — Leaf discoloration produced experimentally by injecting elm seedling with toxic 

 sap from wetwood-afFected elms. The toxic sap caused the leaves to turn dull greenish brown 

 between the veins and along the margins. 



year, of scattered branches. This type of 

 branch dying is evident in the Hinsdale 

 elm pictured in fig. 14. 



Dissected Elm 



An American elm, variety Littleford, 

 that wilted during late July and early 

 August of 1943 was cut up for examina- 

 tion. This tree had two trunk cracks near 

 its base. Both cracks had developed during 

 the previous winter and before the growth 

 of 1943 wood. Both had fluxed earlier in 

 the summer but were callused over by 

 August. One crack, fig. 10, had a 12-inch- 

 long bark callus which extended upward 

 from a point 4 inches above the ground. 

 The inner face of the bark and the wood 

 callus which formed beneath the bark are 

 shown in fig. 17. Fig. 18 shows the crack 

 in the trunk wood after most of the 1943 

 wood adjacent to it had been chiseled off. 



This trunk crack, approximately 18 inches 

 long, extended into the 1938 wood. 



The second trunk crack, fig. 9, was 

 covered by a 2-foot-long bark callus which 

 extended upward from a point about 2 

 feet above the ground. This crack was 

 directly beneath the branches which wilted 

 in the upper part of the tree. Wood callus 

 had developed only in the 1943 woodring 

 of the crack. A cross section of the trunk 

 through the crack, fig. 9, shows wetwood- 

 affected heartwood, which includes most 

 of the 1941 and 1940 woodrings and all 

 older woodrings. Sap which had spread 

 out through the crack from the infected 

 wood into the 1942 woodring and the 

 spring wood of the 1943 ring was carried 

 from the crack up the trunk through 1943 

 spring wood and into the branches, which 

 soon wilted. There was some lateral spread 

 of the sap as it traveled up the trunk. The 

 sap caused brown streaks to form in the 



