XVIL] CLUB-ROOT OF TURNIPS, CABBAGES, ETC. 103 



modia are absorbed into the young turnip plants by the 

 rootlets. It cannot be objected that a plasmodium is too 

 large to find entrance to a plant by the rootlets, for plas- 

 modia are capable of existing in a state of threadlike fine- 

 ness and watery attenuation beyond conception. 



When once in the rootlets, the plasmodia are in the 

 position that best suits them, and in that position they 

 act as true parasites in the host plant, and by their 

 growth excite disease, unnatural distention of the cells, 

 and " club-root." 



The proofs that old club -roots, with their contained 

 ripe spores, can really produce "club -root" disease in 

 growing turnips have many times been given of late 

 years, and the experiments have been several times re- 

 peated by ourselves. They amount shortly to this. If in 

 spring-time turnip seed is planted in pots in virgin mould, 

 the seedlings will come up unclubbed ; but if exactly 

 similar seeds are planted in earth in which old chopped- 

 up clubs have been incorporated, the seedlings will nearly 

 all be at an early period of growth fatally clubbed. 



For the prevention of clubbing, an alternation of crops 

 for two or three years may reduce the disease, for, as far 

 as is at present known, Plasmodiophora Brassicce, Wor., 

 is confined to cruciferous plants. As the spores of the 

 fungus can live for more than a year in dry material, 

 more than one season should elapse before turnips or 

 cabbages are again planted in tainted fields. As char- 

 lock is often badly clubbed, this, with other worthless 

 cruciferous weeds, should not be allowed, more than is 

 possible, to choke the hedge sides of fields under cultiva- 

 tion with cabbages, turnips, and mangels. 



Beyond all other things, it is necessary that old club- 

 root should not be allowed to remain on the ground where 

 turnips or cabbages are to be grown. All the diseased ma- 

 terial should be gathered into a heap, and, if possible, burnt. 



Prof. Jamieson, in the last annual report of the Sussex 

 Association for the Improvement of Agriculture, advised 



