3i6 



Brown-rot of Swedes. 



perfectly sound healthy roots, by inoculation with a pure culture 

 of a bacterium which I isolated from naturally decaying 

 roots, and which proved to be identical with P. campestris. 

 Specially prepared pieces of healthy swede sown with a pure 

 culture, under strictly sterile conditions, soon became infected, 

 showing the brown discolouration of the tissues and all the 

 peculiar characteristics of the attack. Bacteria again isolated 

 from these in the same manner and sown upon similar blocks 

 of swede always produced the same result, leaving no doubt 

 that the disease in question was caused by this particular 

 species of bacterium. 



As will be observed by reference to the figure, this plant had 

 formed a large well-grown root before the infection commenced. 

 This I found most commonly to be the case, and it is in some- 

 what striking contrast to the manner of attack as described by 

 Smith, who found the dwarfing of the plants a strong character- 

 istic. He states that turnips attacked by brown-rot do not 

 enlarge much radially, and that numbers which he examined, 

 though several months old, in form more resembled carrots than 

 turnips. According to this author's observations the infection 

 took place chiefly through the leaves, and presumably his 

 specimens became a prey to the disease at an early age, which 

 would account for the arrested growth. 



So far as I know, this disease has only been reported in 

 England upon cabbages. In America the havoc which it has 

 wrought is very serious. At Racine (Wisconsin) the damage for 

 three years was estimated to exceed ,£20,000. In Illinois the 

 acreage under cabbages has been much reduced, and on Long 

 Island the cabbage-growing industry was threatened with 

 extinction owing to this disease. In some cases entire fields 

 were totally destroyed by it, and the loss throughout the State 

 of New York is said to have amounted to many thousands 

 of dollars. It is reported by Jones * as being widespread in 

 Vermont, and apparently on the increase. The epidemic is 

 stated to have been rampant in no less than eighteen of 

 the States of America, and recent researches of Stewart and 



* Black- Rot, a Disease of the Cabbage and Turnip. Vermont- Agricultural 

 Experiment Station, Burlington, Vt. I. Bulletin No. 66, 1898. 



