August, 1945 



Carter: Wetwood of Elms 



433 



April 1, 1942, and pressure readings, taken 

 periodically, increased from 1 pound on 

 April 14 to 60 pounds on June 20, 1942. 

 The reading was 51 pounds on June 18, as 

 recorded on the gauge, fig. 26. 



On June 20, after the 60-pound read- 

 ing had been made in this Hinsdale tree, 

 the gaugecock started to leak, allowing 

 sap and gas to escape. The next day, June 

 21, the pressure had dropped to 40 pounds. 

 The pressure continued to decrease during 

 the remainder of June and through most 

 of July, and had decreased to 1 1 pounds 

 on July 29. After the installation of a 

 new gaugecock on July 29, trunk pressure 

 again increased, and readings were ob- 

 tained of 28 pounds on July 30, 42 pounds 

 on July 31 and 46 pounds on August 4. 

 Pressure then decreased until it reached 

 1 pound on January 8. During February 

 and March of 1943 the pressure in this 

 tree was too low to register on the gauge 

 being used. A pressure of 2 pounds was 

 read in May of 1943, and on June 2 this 

 tree was fluxing through a trunk crack 

 which apparently had developed the previ- 

 ous winter. The tree continued to Hux 

 through the trunk crack until October. So 

 long as the trunk continued to Hux, pres- 

 sure readings varied between 1 and 2 

 pounds. On October 6 the trunk crack 

 was found to have callused over, and 

 the pressure registered on that day was 

 12 pounds. Subsequent pressure readings 



were 14.2 pounds on October 12, 16 

 pounds on October 27 and 2 pounds on 

 November 30. On December 11, there 

 was not sufficient pressure to register. 



Greenhouse Studies. — The pressures 

 developed in two elms artificially in- 

 fected with wetwood and one elm not in- 

 fected, all grown in the greenhouse, were 

 recorded from November, 1942, through 

 February, 1944. The infected trees had 

 been inoculated with Erivinia riiniipressur- 

 alis in 1941 and had developed typical wet- 

 wood symptoms in the trunk wood during 

 1942. The non-infected tree was used as 

 a check. Gaugecocks were installed in the 

 trunks of all three trees on November 13, 

 1942. In the two wetwood-affected trees, 

 pressures developed which were greater 

 than those normal for healthy elms and 

 similar to those found in naturally infect- 

 ed elms. In one tree a maximum pressure 

 of 8 pounds occurred on June 26 and 

 again on July 3, 1943. In the other tree 

 a maximum pressure of 14.8 pounds was 

 recorded on August 30, 1943. In the check 

 tree no pressure that could be measured 

 with the gauge developed. A water manom- 

 eter was connected to the check tree 

 on October 4, 1943, and a maximum 

 reading of 21 mm., approximately 0.03 

 pound, was recorded on October 21. 



The curve in fig. 28 shows the monthly 

 average of the pressure readings ob- 

 tained from one of the infected trees 



(/I 



Q 



z 

 o 



Q. 



DC 

 D 

 IT) 



m 

 u 

 a. 

 a. 



DEC 

 1942 



JAN FEB MAR APR MAY 



JUN JUL AUG SEP OCT NOV DEC JAN FEB 

 1943 1944 



Fig. 28. — The average monthly pressure recorded during 16 months in one greenhouse- 

 grown elm, artificially infected with wetwood. In the greenhouse, just as in the field, an annual 

 pressure cycle occurs, with the peak pressure in September and low pressures in winter. 



