434 



Illinois Natural History Survey Bulletin 



Vol. 23. Art. 4 



for the period November, 1942, to the 

 end of February, 1944. The maximum 

 pressure in this tree occurred in Septem- 

 ber, 1943. Diseased elms under obser- 

 vation in Hinsdale this same j'ear also 

 produced maximum pressures in Septem- 

 ber. 



The low pressure of 1.5 pounds which 

 occurred in June was recorded while the 

 tree was fluxing through a crack in a 

 branch crotch 3 feet above the gaugecock. 

 To test the effect of drainage on fluxing, 

 the gaugecock was left open from June 7 

 until the crotch stopped fluxing on June 

 11. Then the gaugecock was closed, and 

 fluxing began again on June 15. The 

 gaugecock was reopened at once and the 

 crotch stopped fluxing on June 17. There- 

 after the gaugecock was kept closed, and 



the amount of fluxing was not sufficient 

 from that time on to prevent the formation 

 of callus. The crotch crack was sealed 

 with callus on July 18, and fluxing ceased. 

 Pressure in the trunk of this wetwood- 

 infected tree was found to follow a diur- 

 nal cycle as well as an annual cycle. Both 

 pressure and air temperature readings dur- 

 ing a period of 2 days and 1 night were re- 

 corded on August 3—4 and August 12—13, 

 1943, fig. 29. On August 3, when the air 

 temperature did not go much above the 

 optimum temperature range for the wet- 

 wood organism, the maximum pressure 

 occurred at 1 :15 P.M. On August 4, 12 

 and 13, when the air temperature had risen 

 above the optimum temperature for the 

 organism by 9:00 a.m., the maximum 

 pressure occurred between 8 :30 and 1 1 :00 



100 



100 



wi 95 



a. 

 o 



UJ 



90 



uT 85 

 a. 



80 



75 



70 



READINGS AUGUST 3-4 



PRESSURE IN THE TRUNK 

 AIR TEMPERATURE 



Zl^..^^ 



9 A.M. 



I RM. 



5 RM. 



9 RM. 



I A.M. 



5 A.M. 



9 A.M. 



I PM. 



READINGS AUGUST 12-13 



5RM. 



12 



_!_ 



9 A.M. 



IRM. 



5RM. 



9 RM. 



I A.M. 



5 A.M. 



9 A.M. 



IRM. 



5RM. 



Fig. 29. — Air temperatures and pressures in one greenhouse-grown elm artificially infected 

 with wetwood were recorded during two 34-hour periods. Pressure in the greenhouse tree 

 followed a diurnal cycle. When the air temperature did not go much above the optimum tem- 

 perature for the wetwood organism, maximum pressure occurred at 1:15 P.M. When the air 

 temperature had risen above the optimum temperature for the organism by 9:00 a.m., maximum- 

 pressures occurred between 8:30 and 11:00 a.m. Minimum pressures occurred between 7:05 P.M.^i 

 and 12:10 a.m. 



