54 



BACTERIA IN RELATION TO PLANT DISEASES. 



THE PARASITE. 



Bacterium vascularum (Cobb) Greig Smith* is a honey-yellow organism, occurring in the 

 bundles of diseased sugar-cane as short rods, single, in pairs (mostly), fours, or eights, joined 



end to end (figs. 26, 27). Sometimes the rods are clumped 

 in the stem, i. e., in the form of pseudozoogloeae. The 

 organism is motile by means of a single polar flagellum 

 (RGS., EFS.f). This is easily demonstrated according 

 to Greig Smith by using the night-blue method and agar 

 cultures (fig. 28). They were stained in the writer's labora- 

 tory by Lowit's method, using young agar cultures (fig. 29) . 

 The motility is more evident in young cultures than in old 

 ones. The organism is generally non-motile when crowded 

 in the bundles of the stem. This restricted motility is, 

 however, observed under similar conditions in many other 

 bacteria (see Bad. campestre, vol. II, p. 316). Rods stained 

 and embedded in balsam have an average measurement of 

 0.4 X i M ( RGS. ) . Fig. 30 is from a young culture on agar. 

 The writer's measurements are as follows: 



Bacterium vascularum from tissues of inoculated plant No. 4, stained with 



carbol fuchsin; slide 466 h 10; average size 0.9X0.4/1; another 



slide 0.88 to 1.0/1X0.3 to 0.35/1. 

 Plant No. 6, tissues stained with carbol fuchsin; average size, 0.65 to i.2/j 



X 0.3 to 0.5/1. 

 Plant No. 10, tissues stained with carbol fuchsin; average size, 0.6 to 1.4/1 



X 0.3 to 0.4/1. 

 Plant No. 35, smear stained with carbol fuchsin; average size, i to 1.4/j 



X 0.35 to 0.5/1. 

 Agar culture, 8 days old, stained with Lowit's flagella stain, slide 8, January 



1 1, 1906; average size, 1.2 to 1.5/1 X 0.45 to 0.55/1. 



No spores have been observed (EFS., RGS.). It is 

 stained fairly well by Gram's method, 4 min. stain, 2 min. 

 iodine (it does not stain by Gram, according to Greig 

 Smith). Carbol violet followed by dilute alcohol produces 

 the best films, while the blues stain it but feebly (RGS.). 

 The organism stains well with carbol fuchsin. The writer 

 had poor success with Loeffler's alkaline methylene blue. 



Bacterium vascularum is easily isolated from diseased 

 canes (when not too old) by means of Petri-dish poured 

 plates. On plates of standard nutrient agar at 25 C. the 

 colonies come up rather slowly, i. e., in 7 to 10 days, so 

 that often for the first few days well-sown plates will ap- 

 pear sterile, or only sparsely spotted with intruding colo- 

 nies. This will be better appreciated if I give transcripts 

 from notes (made on the fourth, sixth, and eleventh days) 

 of nine Petri-dish poured plates made from the interior of 

 inoculated cane No. 1 1 : 



Fourth day. Many of the organisms must have been dead. 

 There are as yet no growths on the plates, except one or two 

 colonies which are not Bad. vascularum. 



Sixth day. Plate I, one colony which has become yellowish, 

 but is much too opaque for Bad. vascularum. Plate II, one 

 small white colony. Plates III and IV, nothing. Plate V, one 



Fig. 24.{ 



'Synonyms: Bacillus vascularum Cobb; Pseudomonas vascularum (Cobb) EFS. 



fRGS. = R. Greig Smith; EFS. = Erwin F. Smith. 



JFiG. 24. Longitudinal section through cane No. 30 (common purple) inoculated May 5, 1903. Only slightly 

 diseased (the red bundles show here as dark stripes) and disease confined to the vicinity of the nodes which bore the 

 inoculated leaves. Plates were poured. Photographed January 5, 1904. 



