768 ' CLUB-ROOT ' DISEASE 



Gas lime has little or no effect upon Plasmodiophora. An 

 acid condition of the ground or the application of acid manures, 

 such as superphosphate of lime, encourages the organism, while 

 alkaline compounds diminish its power of attack. 



Ex. 321. — Dig up a 'clubbed' cabbage and note the form and position of 

 the thickened parts. Cut across the undecayed thickened parts of a small 

 secondary root and examine with a pocket l«ns. Observe the small white 

 opaque spots : are they more abundant in the centre or near the outside ? 



Compare the colour of the interior of a large swelling which has begun to 

 decay. 



Ex. 326. — Cut across the knob-like thickenings at the upper part of the 

 diseased root of a cabbage or the small round lumps on the outside of a 

 turnip ' bulb. ' If hollow, look for white larvae of insects. 



Ex. 326. — Examine thin sections of 'clubbed' parts of a cabbage root in 

 water with a \ inch and then with J or J inch objective. Make sketches of 

 the Plasmodia and spores in situ. 



Ex. 327. — Where 'clubbing' is prevalent, make a note of the kind of soil 

 on which the plants are growing — whether stiff clays, light sands, loams, or 

 chalky soils. Take small samples of each soil, place them in evaporating 

 dishes and pour hydrochloric acid over each ; note the amount of effervescence 

 produced in each case. 



