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Illinois Natural History Survey Bulletin 



Vol. 23. Art. 4 



Pig. 5. — Fluxing through branch crotches is 

 common in elms affected with wetwood. The 

 flux on this tree, invaded by air-borne organ- 

 isms, has coated the bark below the crotch 

 with slime. 



In most elms, wetwood is confined to 

 the inner sapwood and heartwood, and 

 there is very little or no streaking in the 

 outer sapwood and no discoloration in 

 the cambial region or phloem. However, 

 in those affected elms that exhibit wilting 

 of twigs and branches, grayish brown dis- 

 coloration can be found in the outer 

 sapwood and occasionally in the cambial 

 region and phloem as well* as in older 

 wood. 



Gas. — In wetwood-affected tissues, gas 

 is produced in large amounts by the action 

 of the fermenting bacteria on carbohy- 

 drates and other materials in the trunk. 

 This gas, confined in the trunk, causes 

 abnormally high sap pressures to develop. 

 Pressures up to 60 pounds per square inch 

 have been recorded. 



Sap. — Sap accumulates in abnormally 

 large amounts in affected wood. Because 

 of the abnormally high pressure caused by 

 the gas produced by fermentation, sap 

 frequently is forced out of the trunk 



Fig. 6. — This elm is fluxing through a crack 

 in the trunk, which originated as a frost 

 crack during the preceding winter. Fluxing 

 through the crack in the bark became apparent 

 by June. 



