THE FUNGI WHICH CAUSE PLANT DISEASE 



35 





] 



high. In these plants the vessels become plugged with pure cul- 

 tures of Ps. stewarti from tip to base. Small holes filled with 

 yellow slime appeared later in the parenchyma. Wounds were en- 

 tirely unnecessary to infection, though the vessels are the primary 

 seat of disease. 



Ps. syringae v. Hall '^ causes disease of Syringa and other plants. 



Ps. tumefaciens (S. & T.) Stev.'^"'* (Group number 

 212.2322023.) Vegetative cells taken directly from a gall usually 

 0.6 to 1.0 M X 1.2 to 1.5 M. • 



When grown on agar for two days 2.5 to 3 ju x 0.7 to 0.8 fi or 

 occasionally wider. Endospores not observed. Motile by means 

 of one, sometimes two or three terminal flagella; viscid on agar 

 but capsules not demonstrated. Readily stained in ordinary basic 

 anilin stains; Gram negative. Agar surface colonies usually come 

 up in from four to six days at 25°, 

 white, smooth, circular; margin even, 

 shining, semi-transparent, maximum 

 size 2 to 4 mm. Agar streak; growth 

 moderate, filiform. On sterile potato 

 cylinders growth more rapid, in one 

 or two days covering the entire surface 

 of the cylinder; smooth wet-glisten- 

 ing, slimy to viscid, odorless; potato 

 cylinder grayish, darker with age, 

 never yellow. Gelatine colonies dense, 

 white, circular, small, non-liquefying, 

 medium not stained. In beef broth 

 clouding often absent or inconspicuous, rim of gelatinous threads 

 present, also more or less of pellicle; in young cultures very deli- 

 cate suspended short filaments, best seen on shaking. Milk coagu- 

 lation delayed; extrusion of whey begins only after several days; 

 litmus milk gradually blued, then reduced. Cohn's solution, 

 growth scanty or absent, medium non-fluorescent. 



No gas produced; organism aerobic in its tendencies; nitrates 

 not reduced. Indol produced in small quantity, slowly. Slight 

 toleration for citric, malic, and acetic acids. Toleration for alkali 

 slight. Optimum reaction between +12 and +24, Fuller's 

 scale. T. D. P. 51°. Opt. between 25° and 28° Max. ±37°. Growth 



Fig. 22.— Flagella of Pa. tumefa- 

 ciens, various stains. After 

 Smith. 



