August, 1945 Carter: Wetwood of Elms 



Table 1. — Summary of isolations obtained from 346 elms which showed wetwood. 



419 



In all of the branch and trunk samples 

 cultured, the diseased condition was indi- 

 cated by brown streaks or other abnormal 

 brown discoloration. The number and 

 type of samples cultured, the number of 

 bacterial isolates obtained and the per cent 

 of samples from which bacteria were 

 isolated are given in table 1. 



The types of materials samples, listed 

 in table 1, were branch sapwood and heart- 

 wood, trunk sapwood, heartwood and 

 phloem, and sap from wetwood-affected 

 trunk wood. Isolates of bacteria were 

 obtained more frequently from heartwood 

 than from sapwood and from a greater 

 per cent of the trunk samples, approxi- 

 mately 77 per cent, than of the branch 

 samples, approximately 39 per cent. Bac- 

 teria were present in all sap samples test- 

 ed, indicating that sap of wetwood- 

 affected trunk wood is constantly infested 

 with bacteria. These data indicate that 

 bacteria are more abundant in the trunk 

 wood, where they live over from year to 

 year, than in the brown discolored branch 

 wood. Crandall (1943) found that, in 

 Platanus acerifolia Willd., fermenting 

 bacteria were limited mainly to the inner- 

 most rings, and he concluded that these 

 bacteria usually did not readily attack the 

 healthy tissues of well-established trees. 



Histology 



Histological studies were made on 

 tissues from 1 1 elms affected with wet- 

 wood. The tissues examined included 

 branch xylem, root xylem, trunk xylem, 

 trunk cambium and trunk phloem. Many 

 vessels affected with wetwood, especially 



those of the trunk xylem, contained 

 tyloses, bacteria and gumlike materials. 

 Some vessels, fig. 19, were filled with 

 large, thin-walled tyloses while others had 

 small tyloses which covered only the inner 

 vessel walls. Tyloses were formed by 

 August in current-season wood of wet- 

 wood-affected elms which wilted during 

 July. They appeared to be sufficiently 

 abundant in some vessels to retard and 

 possibly prevent the flow of sap. 



Masses of bacteria were present in 

 scattered vessels and ray cells. Bacteria 

 were more abundant in trunk xylem than 

 in branch xylem. The limited occurrence 

 of bacteria in the branch xylem explained 

 why they were not isolated so frequently 

 from branch samples as from trunk sam- 

 ples. There was no evidence of tissue 

 disintegration in the infected wood. 



Light brown deposits of what appeared 

 to be gum were observed in a few scat- 

 tered vessels and ray cells. Occasionally 

 cells appeared to be filled with this gum, 

 but most frequently the gum appeared to 

 be deposited on the cell walls. Ogilvie 

 (1924) reported medullary rays and wood 

 parenchyma of water-soaked elm wood to 

 be filled with a gummy substance, com- 

 posed partly of tannin and partly of 

 starch, that gave the wood a brown color. 



Fungi were not found in any of the 

 wetwood-affected tissues that were ex- 

 amined. 



The formation of callus over a trunk 

 incision on a 2-year-old elm seedling sub- 

 merged in water occurred within 1 1 

 days. The callus tissues were laid down 

 by xylem, cambium and phloem. That no 

 callus formed over a trunk incision of 



