430 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 4 



leader. Each cut leader remained in its 

 respective solution for 5 days. As each 

 bottle was removed, the cut end of the 

 leader was wrapped with rubber tape to 

 prevent the wood from drying out. 



Filtrate of wetwood sap, of which 291 

 ml. were taken up in 5 days, caused 

 browning and wilt of foliage on the two 

 upper branches nearest the cut end of 

 the treated leader ; the two branches were, 

 respectively, 9 and 12 inches below the 

 cut. Browning appeared within 24 hours, 

 wilt within the next 24 hours. Leaves near 

 the base of the two branches turned brown 

 and wilted 24 hours before the leaves at 

 the tips. All of the leaves, 50 in number, 

 on these two branches wilted and turned 

 brown within 72 hours, and abscised 

 within 10 days. In 45 days the treated 

 leader had died back 8 inches, to within 

 1 inch of the uppermost lateral branch. 

 Additional dieback had not occurred at the 

 end of 3 months. On subsequent exam- 

 ination a light tan water-soaked condition 

 was found in the current-season wood, 

 especially noticeable in the spring wood ; 

 this condition extended down the stem 30 

 inches. 



Wetwood sap, of which 41 ml. were 

 absorbed in 5 days, caused slight browning 

 of leaves on the first lateral below the 

 treated leader. However, none of the 

 foliage wilted. The treated leader died 

 back 5 inches in 45 days. 



The wetwood organism, Erwinia n'uni- 

 pressuralis, in nutrient broth, in sterile 

 distilled water, and autoclaved in sterile 

 distilled water, did not cause any browning 

 or wilting of leaves. Filtrate of nutrient 

 broth staled with fermenting wetwood 

 bacteria did not cause wilt but prevented 

 callus formation on the end of the cut 

 leader. 



Callus developed normally on the cut 

 leaders immersed in sterile distilled water 

 and nutrient broth culture of Erwinia 

 nimipressuralis after a slight initial killing 

 of the cut bark had occurred. It is possible 

 that bark on the leader immersed in water 

 was killed by mechanical injury when the 

 leader was cut. Callus formation was not 

 retarded on the cut leaders which were 

 immersed in water suspensions of living 

 and autoclaved E. nimipressuralis. 



In this experiment, browning and water- 

 soaked appearance of the wood was not 

 characteristic of any one treatment. A 



water-soaked condition developed when 

 wetwood sap, its filtrate, nutrient broth 

 culture of fermenting wetwood bacteria 

 and its filtrate were used. Fine brown 

 streaks developed in current-season wood of 

 the cut leaders when they were immersed 

 in sterile distilled water, a nutrient 

 broth culture of Erwinia nimipressuralis , 

 its filtrate, and a suspension of it in sterile 

 distilled water, but this streaking was not 

 characteristic of that found in wetwood- 

 affected trees in the field. The trees treat- 

 ed with sterile distilled water, a nutrient 

 broth culture of E. nimipressuralis, its 

 filtrate, a suspension of it in sterile dis- 

 tilled water, and an autoclaved suspension 

 of it in sterile distilled water, continued 

 to grow normally throughout the experi- 

 ment, except for the lack of callus for- 

 mation at the cut on each leader, as 

 pointed out above. 



Pressures in Affected Elms 



Field Studies. — In these studies, the 

 presence of gas and sap under pressure 

 in tree trunks was first noticed in 1941 

 while increment borings of the diseased 

 trunk wood of wilting elms were being 

 taken. From some trees, a considerable 

 amount of gas and sap Howed out through 

 the increment borer tube (auger) and 

 continued to flow out of the hole in the 

 tree trunk after the increment borer was 

 removed. This flow was accompanied by 

 bubbling and fizzing sounds, indicating 

 that gas was dissolved under pressure in 

 the sap. 



According to the studies of MacDougal 

 (1932), MacDougal & Working (1933), 

 and Beilmann (1940), pressure in trunks 

 of healthy trees, various kinds, is never 

 great, never as much as 1 pound, and is 

 altered mainly by changes in external air 

 temperature. Stautz (1931), Dodge 

 (1937) and May (1942) have pointed 

 out that abnormally high pressures de- 

 velop in the trunk wood of trees affected 

 with wetwood. 



During 1941, as part of this investiga- 

 tion, the pressures in the trunks of 22 wilt- 

 ing elms that were affected with wetwood 

 were measured with a pressure gauge 

 attached to an increment borer, fig. 25. 

 Pressure readings were taken after the 

 wood core had been removed from the ' 

 auger and the increment borer had been 





