420 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 4 



Fig. 19. — Cross section of xylem of elm affected with wetwood, showing tyloses in many 

 vessels. Bacteria are occasionally present in some of the vessels. They are observed most 

 frequently where tyloses are abundant. X130. 



a second 2-year-old seedling when the cut 

 portion of the stem was submerged in sap 

 from a diseased elm indicates that such 

 sap prevents or at least retards the forma- 

 tion of callus. Many of the ray and 

 parenchyma cells near the surface of the 

 trunk incision which was submerged, in 

 sap became filled with brown, gumlike 

 material. 



The Wetwood Organism 



Five bacterial isolates, representative of 

 the numerous isolates obtained from elms 

 affected with wetwood, each obtained 

 from a different elm, were studied for 

 their morphology, cultural characters and 

 biochemical reactions. Isolates 1, 3, 4 and 

 5 were obtained from wetwood-affected 

 elms which had wilted. Isolate 2 was 

 obtained from a wetwood-affected elm 

 which had not wilted. Isolates 1, 2 and 4 

 were from parkway trees, while isolates 

 3 and 5 were from nursery trees. 



Morphology. — These five isolates are 

 believed to represent a single species of 

 bacterium. The organism is a short rod 



with rounded ends and occurs singly or, 

 rarely, in pairs or chains, fig. 20. Cultures 

 on potato dextrose agar (pH 6.8) incubat- 

 ed at 24 degrees C. for 48 hours produced 

 cells measuring 0.68-2.00x0.34-0.68/. 

 mostly 0.68-1.35x0.34-0.68/;.. This or- 

 ganism is Gram-negative, motile, not acid- 

 fast, and has up to six peritrichiate flagella 

 measuring up to 11 /a long, fig. 21. Cap- 

 sules and spores were not observed. 



Cultural Characters. — Growth in 

 nutrient broth appears in 24 hours or less 

 and the broth becomes strongly clouded 

 or turbid, with a decided kidney bean 

 odor. The organism usually forms a thin 

 pellicle or flocculent surface growth when 

 undisturbed. Sediment is usually scant 

 and viscid but becomes abundant if cul- 

 tures are disturbed at frequent intervals. 

 The medium becomes strongly alkaline. 

 Colonies on potato dextrose agar incubat- 

 ed at 24 degrees C. for 24 hours are 

 circular, smooth, entire, flat to slightly 

 raised, and usually opaque (whitish 

 cream) but occasionally somewhat trans- 

 lucent. Growth in streaks on potato dex- 

 trose agar is abundant, spreading, glisten- 



I 



