HACTKRIUM CAMPJ^STRE IX SOUTH AFRICA. 403 



The staining of the veins of the fohage leaves is also evi- 

 dent in diseased kohl-rabi, and the fibro-vascular bnndles in the 

 swollen stem are also conspicuously blackened ( I'late ii, a). 

 The stems fail to increase in size as they should do, and finally 

 necrosis takes place and results in a large central cavity with 

 a brown fibrous lining (Plate ii, b). Before they reach this 

 stage, however, the plants are frequently invaded by soft rot 

 bacteria, which rapidly complete the work of destruction. 



In the specimens of swedes which have come under my 

 notice, the leaves were comparatively healthy, but the roots 

 failed to develope in the normal manner. \\^hen cut open the 

 fibro-vascular bundles were found to be blackened, and in the 

 majority of cases a central cavity was forming similar to that 

 described as occurring in afifected kohl-rabi plants (Plate lo. b). 



The above-mentioned hosts are the only ones which have 

 been found to be afifected in this country up to the present, and 

 the inoculation experiments conducted with pure cultures of the 

 organism have been restricted to these plants, but in America 

 Smith has also observed the disease in collards. kale, rape, ruta- 

 baga, charlock, and radish, and has successfullv inoculated the 

 majority of these plants. It is probable that, with continued 

 observation, additions will be made to the list of hosts in which 

 the organism occurs in South Africa. 



Etiology. 



A yellow, one-flagellate bacterium was isolated in Septem- 

 ber, 1914, from cabbages in the writer's garden, Pretoria, which 

 showed typical signs of the disease. On September 25th, four 

 young cabbage plants were inoculated by placing small quantities 

 of an agar streak culture on the edge of the leaves ; the plants 

 were kept moist by covering them over with a bell- jar for 24 

 hours after inoculation. This precaution was also observed in 

 all subsequent experiments. On the tenth day, small areas near 

 the edge of the leaves were slightly wilted, and a closer exam- 

 ination showed a distinct discolouration of the veins ; these 

 symptoms were much more mai'ked after another five days. 

 Microscopic examination showed ihat the fibro-vascular bundles 

 were covered with bacteria, and the organism was re-isolated 

 without any difficulty. In another two weeks these seedlings 

 were completely wilted off; the controls were perfectly healthy. 



A second experiment was carried out under similar condi- 

 tions, using young plants in pots. Six cabbages and three 

 swedes were inoculated by needle pricks with a culture obtained 

 from the same source as that used in the previous experiment. 

 All the cabbages showed distinct signs of infection on the 

 eleventh day; the swedes, unfortunately, were completely 

 destroyed by insects. All the controls remained clean. 



An experiment with swedes carried out on a larger scale 

 was also unfortunate, the ])lants being destroyed by hail before 

 anv results could be obtained. 



