. Bulletin. Natural history; Natural history. HEALTHY ELM. WETWOOD-AFFECTED ELM _i_ - 1422 I o °- Ui a. in in UJ a. a. .01422 9 AM. I I 12 M. I 2 PM. 3 -| 4 2 0 i/i o z o a. u" cc D in in UJ a. Fig. 30.—Air temperatures, internal trunk temperatures in a healthy tree, and pressures in a healthy tree and in a wetwood-atfected tree, all three trees greenhouse-grown; recorded on November 16, 1943. The trunk temperature curve and the pressure curve for the healthy trees are similar in shape to the air temperature curve. A rapid drop i
. Bulletin. Natural history; Natural history. HEALTHY ELM. WETWOOD-AFFECTED ELM _i_ - 1422 I o °- Ui a. in in UJ a. a. .01422 9 AM. I I 12 M. I 2 PM. 3 -| 4 2 0 i/i o z o a. u" cc D in in UJ a. Fig. 30.—Air temperatures, internal trunk temperatures in a healthy tree, and pressures in a healthy tree and in a wetwood-atfected tree, all three trees greenhouse-grown; recorded on November 16, 1943. The trunk temperature curve and the pressure curve for the healthy trees are similar in shape to the air temperature curve. A rapid drop in air temperature between 1:00 and 1:10 did not cause a similar drop in pressure in the wetwood-affected tree. Pressure in the diseased tree did not decrease until the air temperature dropped below degrees F. Zero represents atmospheric pressure. cycle in wetwood-affected trees is not in- fluenced by changes in air temperature, as long as the air temperature is in the opti- mum range for the organism. However, air temperatures above and below the op- timum range for the organism apparently influence the rate of fermentation and thus affect pressure. Pressure and air temperature readings were taken at 15-, 30- or 60-minute inter- vals on 17 days between August 2 and September 1 and on 15 days between September 29 and November 16, 1943. For the 17 days, maximum pressures oc- curred most often at 11:00 , while maximum temperatures occurred most often at 1 :00 For the 15 days, both about 11 :00 , when the maximum air temperature is above the optimum tem- perature range for the wetwood organism. However, when the maximum air tem- perature is not above the optimum tem- perature range of the organism, pressure and temperature both reach their maxima at about 1 :00 The pressure cycle does not reach a second peak during any one day, regardless of the variations in air temperature. This experiment indicates, as did the previous one, that the diurnal pressur
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