228 



Black Rot of Cabbages, Turnips, &c. [July, 



This disease (Pseudomonas campestris, E. Smith) is very 

 prevalent in the United States, and during recent years has 

 occurred in various European countries. 

 Black Rot of Cabbages, It is of bacterial origin and causes the 

 Turnips, &c. plant to rot and form a pulpy foetid- 

 smelling mass. Cauliflowers, cabbages,. 

 Brussels sprouts, radishes, white and swede turnips — in fact all 

 cultivated plants belonging to the Crucifer family are attacked. 

 The lower leaves are usually infected first, the germs entering 

 the substance of the leaf through minute openings (water 

 stomata) situated along the margin, or through wounds caused 

 by the punctures of insects, &c. In cases where the soil is 

 infected the germs may gain an entrance to the plant through 

 broken roots at the time of transplanting. When the bacteria 

 are once inside the leaf they multiply rapidly and are confined 

 to the veins, from whence they pass down the leaf-stalk into the 

 stem. From the stem they quickly pass into the stalks of other 

 leaves, so that within a short time every leaf is infected. As. 

 the bacteria travel along the veins and the vascular bundles of 

 the leaf-stalks and stem a dark brown or blackish substance 

 is deposited, which causes the veins to show up as a black 

 network ; the vascular bundles of the leaf stalk and the stem 

 also appear as black points or a blackened ring when cut across. 

 The presence of this blackening of the veins is a certain indica- 

 tion of the presence of the disease, and infected plants should 

 be promptly removed and burned — not buried nor used as 

 food for cattle or pigs, otherwise the result will be infection of 

 the land sooner or later. It has also been proved that the 

 germs are conveyed from diseased to healthy plants by insects. 

 Rotation of crops is advisable ; cereals, potatoes, and legumes 

 are not attacked In this country rape appears to be most 

 susceptible to the disease. In an extensive trial plot of various 

 kinds of cabbages, savoys, Brussels sprouts, &c, those that 

 contained " rape blood " were first attacked, whereas those 

 strains without a taint of rape were the last to succumb. 



It has been considered by growers that the disease can be 

 transmitted by means of the seed, and this idea has been proved 

 to be correct by Harding, Steward, and Prucha, who have 

 shown that in the United States much of the cabbage seed offered 

 for sale is contaminated with the germs of black rot disease.. 



