CHAPTER LI. 

 'CLUB-ROOT' DISEASE. 



Symptoms.- — This disease, which is variously known as 'club- 

 root,' ' finger-and-toe,' 'anbury' and 'canker,' attacks many 

 species of cruciferous plants, and is especially destructive to 

 the cultivated species of Brassica, such as turnips, swedes and 

 cabbages. It is worthy of note that certain races of these plants 

 are more subject to the disease than others ; cauliflowers and 

 Brussels sprouts, for example, are very liable to it, while the 

 kails are capable of resisting its ravages to a considerable extent. 



The disease appears to make greatest progress in summer ; the 

 earlier spring vegetables in gardens often escape altogether, or 

 suffer very little from it. 



Infected young plants show irregular thickening and knob-like 

 swellings on their roots. The diseased parts, when cut across, 

 are solid and of greyish colour, mottled with small, white, opaque 

 patches. As the plants increase in age, the swellings become 

 larger and larger, often reaching the size of a man's fist (Fig. 258). 

 The upper parts of the plant develop very slowly ; cauliflowers 

 and cabbages attacked by the disease make little or no ' head,' 

 all the nutriment prepared in the few expanded leaves of the 

 plant being used up in the growth -of the swollen roots. 



The 'clubbed' parts after a time turn brown and decay; in 

 dry soils the rotten portions become brittle and fall into powder 

 or small fragments ; while in damp, stiff" soils the decayed mass 

 is semi-liquid, and emits an offensive odour. 



Although the plants produce adventitious roots when the 

 natural roots are destroyed, these new roots soon become in- 



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