Gibbs (1931) summarised the occurrence in New Zealand of club root in crucifers caused by Plasmodiophora; he suggested for its control a liberal application of lime prior to sowing, and the use of resistant crop varieties. In further work (Gibbs, 1934) her, recommended drenching infected areas with 0.1 % acidulated mercuric chloride solution at the rate of 2 gallons per square yard. Resistance has been bred into Swedes and turnip varieties suitable for New Zealand conditions, e.g. 'N.Z. Wilhelmsburger Swede', the `Wye Swede' 'N.Z. Purple Resistant' turnip, and 'N.Z. Green Resistant' turnip. In some districts this resistance has broken down, and Lammerink (1964, 1965a, b) showed that there were at least seven races of Plasmodiophora present in New Zealand; he pointed out that continuous cropping with the same resistant variety will at times select races of the fungus that are adapted to previously resistant varieties of the host plant. In vegetable crops varieties resistant to local races of Plasmodiophora have been bred for the control of club root on cabbage and cauliflower. Watson (1965) recommended the dipping of plants in a slurry of calomel when transplanting from the seed bed.