August, 1945 



Carter: Wetwood of Elms 



445 



not spread below the region of grafting 

 in Moline or other grafted types of elms. 



In the experimental work reported here, 

 buds, leaves, branch and trunk phloem, 

 trunk cambium and current trunk sap- 

 wood inoculated with the wetwood organ- 

 ism did not become infected. Trunk heart- 

 wood and older sapwood inoculated with 

 fermenting bacteria became infected, and 

 topical wetwood was produced. However, 

 the trees in which the heartwood became 

 infected did not wilt during the 3 years 

 they were under observation. 



In the trunks of elms affected with wet- 

 wood, high pressures develop, whether the 

 trees wilt or not. These pressures common- 

 ly reach 5 to 30 pounds per square inch, 

 and are highest in trees that do not flux. 

 In trees which flux freely, there usually is 

 very little or no pressure. A pressure of 

 60 pounds per square inch was recorded 

 in one elm in 1942. This tree fluxed freely 

 in 1943 and, while fluxing, developed a 

 pressure of only 1 to 2 pounds. Pressure 

 is absent in February and March but be- 

 gins to develop in April and early May. 

 It increases until August or September; 

 then decreases until late December or 

 January. Pressures recorded in artificially 

 infected greenhouse elms followed the gen- 

 eral annual pressure cycle observed in 

 naturally infected elms and were too low 

 to be measured with a gauge when the 

 trees were dormant. 



In artificially infected greenhouse elms, 

 a diurnal pressure cycle was observed. The 

 maximum pressure occurred about 1 1 : 00 

 A.M. in June, July and August and about 

 1:00 P.M. in October, and the minimum 

 pressure occurred usually between 7:00 

 P.M. and 11 :00 p.m. The amount of pres- 

 sure that developed in the greenhouse trees 

 was influenced by air temperature. When 

 : the temperature fell much below the opti- 

 mum temperature range of the wetwood 

 organism — 23 to 30 degrees C. or 75.2 

 to 86.0 degrees F. — pressure in the trees 

 1 decreased. The pressure recorded in a 

 j greenhouse elm not affected with wetwood 

 never exceeded 21 mm. of water, approxi- 

 mately 0.03 pound per square inch, as 

 I measured by a water manometer, but the 

 maximum pressure recorded in one green- 

 i house tree affected with wetwood was 

 I 14.8 pounds. The diurnal rise and fall of 

 I the pressure curve for a normal tree, of 

 the trunk temperature curve and of the 



air temperature curve corresponded close- 



ly- 



Samples of gas from wetwood-affected 

 elms contained approximately 46.4 per 

 cent methane, 33.8 per cent nitrogen, 14.3 

 per cent carbon dioxide, 4.5 per cent oxy- 

 gen and 1.0 per cent hydrogen. Carbon 

 monoxide and illuminants were absent. 



Samples of sap from wetwood-affected 

 elms contained phosphates and an abun- 

 dance of potassium. Although tests were 

 made for them, the following elements 

 and compounds were not found: calcium, 

 chlorides, copper, iron, magnesium, man- 

 ganese, sulfates, zinc, nitrates, nitrites, 

 ammonia, starch, reducing sugars, indole 

 and erythrodextrin. 



The sap and diseased wood of wetwood- 

 affected elms are alkaline, while both sap- 

 wood and heartwood of normal trees are 

 acid in reaction. 



Erwinia nimipressuralis has an optimum 

 temperature range of 24 to 30 degrees C, 

 75.2 to 86.0 degrees F., a maximum tem- 

 perature of 37 degrees C, 98.6 degrees 

 F., and a minimum temperature of 5 de- 

 grees C, 41 degrees F., or less. 



Summary 



1. Our investigation of wetwood of 

 elms was started in 1939. In Hinsdale, 

 1939-1943, 284 elms wilted because of 

 wetwood infections in their trunks. None 

 of the 284 elms which wilted died, and 

 only 73 wilted in more than 1 year. 



2. Wetwood infection has been found 

 in the American elm {Ulmus americana 

 L.) and its cultivated varieties Moline and 

 Littleford, and in the slippery elm (Ulmus 

 fulva Michx.), the English elm {Ulmus 

 procera Salisb.) and the Siberian elm 



{Ulmus putnila L. ). Samples from 346 

 elms located in 21 counties of Illinois 

 were cultured, and the wetwood organism 

 was isolated from 239 of them. Of the 

 346 trees, 292 showed wilt at the time the 

 samples were taken. 



3. Histological studies show the wet- 

 wood bacterium to inhabit principally the 

 vessels and ray-cells of the trunk. It does 

 not grow in sufficient abundance to cause 

 general clogging of the conducting tissues 

 and it does not cause disintegration of the 

 tissues it inhabits. 



4. Wetwood and flux were produced by 

 trunk wood inoculations with this bacte- 



