BACTKRIUM CAMPKSTRE IN SOUTH AFKHA. 409 



It occurs in this country on cabbage, cauHflower, kohl-rabi 

 and swede, possibly also on other cruciferous plants. 



The disease is due to Bacterium aunpestre (Pam.) Sm., 

 which has been isolated from diseased tissues, and a number of 

 successful inoculations have been carried out. 



The organism was found on imported seed offered for 

 sale in Pretoria, and successful inoculations made with the 

 culture so obtained. 



A resume of the characters of the South African organism 

 is given, and these correspond with those of B. campestre. 



It is suggested that as a precautionary measure all seed of 

 cruciferous plants be disinfected before planting. 



Explanation ok Illu.stkations. 



Plate 8. Leaves from a cabbage infected with "black rot"'; the 

 blackened veins are very evident. Natural infection. 

 Groenkloof Experiment Station, near Pretoria. 



Plate 9, a. Infected plants in Laboratory ."-rounds. The cil)- 

 bage in the centre was one of six which were inoculated 

 with ])ure cultures of B. cauipestrc. Photographed two 

 months after inoculation, when infection had spread to 

 neighbouring plants. For fuller explanation see text. 



Plate 9, /;. .Section through stem of cabbage in centre of (a). 



Plate 10, a. Transverse and longitudinal sections through stem 

 of cabbage infected with Bacterium campestre. 



Plate 10, /'. Section through diseased swede. 



Plate II. Sections through kohl-rabi grown at (iroenkloof 

 Experiment Station. 



a Shows characteristic Ijlackening of fibro-vascular 

 bundles. In b a cavity is forming in region of diseased 

 bundles. 



Fig. I. Bacterium campestre from a 24-hour-old culture on 

 nutrient agar ; stained by Ellis's modification of Loeffler's 

 stain. Drawn with camera lucida, Zeiss 1/12 oil imm. 

 objective, and No. 12 compensating ocular. 



Fig. 2. Section through fibro-vascular bundle of the stem of a 

 cabbage seedling artificially infected through the water 

 pores with a pure culture of B. campestre. Drawn with 

 camera lucida, Zeiss ]^/J2 oil imm. objective, and No. 6 com- 

 pensating ocular. 



Fig. 3. Section through another part of the stem from which 

 Fig. 2 was taken. Same magnification as Fig. 2. 



•In these two drawings the dots are not intended to 

 represent the size of the bacteria, but only to indicate their 

 distribution. 



