August, 1945 



Carter: Wetwood of Elms 



431 



backed up several turns to allow for the 

 greatest possible exposure of diseased 

 wood adjacent to the hole in the trunk. 

 This procedure eliminated errors that 



Fig. 25. — Apparatus used for measuring 

 pressure in trunks of elms affected with wet- 

 wood. The gauge is attached to the outer end 

 of the increment borer auger. Pressure is 

 recorded by the gauge when the auger enters 

 the wetwood-affected wood, but pressure read- 

 ings are taken only after the wood core has 

 been removed from the auger. (See text, pages 

 430 and 431.) 



might have resulted from compression of 

 the air in the auger. Pressures read in 13 

 of the 22 trees ranged from 1.0 to 16.5 

 pounds. No apparent relation existed 

 between the pressures read and the 

 amounts of branch wilt observed. The 

 higher pressure readings were obtained 

 from trees which either were not fluxing 

 or were fluxing only slightly through 

 cracks in crotches, pruning wounds and 

 other external wounds. However, those 

 trees which gave high pressure readings 

 fluxed strongly through the holes made 

 by the increment borer. All cores obtained 

 with the increment borer from trees giving 

 high pressure readings were discolored 

 dark brown, especially noticeable in the 

 older sapwood and heartwood, and they 

 had a fermentation odor. 



Pressures recorded in wetwood-affected 

 trees in 1941 were so abnormally high in 

 comparison with the pressures found in 

 healthy elms that additional readings were 

 taken in 1942 and 1943. On April 1, 1942, 

 gaugecock connections were installed, fig. 

 26, on eight elms at Hinsdale. Readings 

 were taken at irregular intervals during 

 1942 and 1943. 



In 1942, pressures greater than could 

 be accounted for by changes in the outside 

 air temperature or barometric pressure 

 began to develop during April. These 

 pressures continued to increase and reached 

 a peak in August. After they had reached 

 the peak, they gradually declined and 

 had reached zero by February, 1943. 



Fig. 26. — Gauge and gaugecock connection used to obtain pressure readings of elms affected 

 with wetwood. This type of gaugecock connection made it possible to obtain pressure readings 

 at will without the escape of gas and sap from the trunk. 



