332 Presents. [Feb. 14, 



B. Experiments conducted with Sterilised Soil. 



5. Two pots of soil, sterilised by steam, were infected with the crushed 

 roots of diseased cabbages. The soil in one pot was mixed with 

 quicklime, that in the other with bone manure, having an acid 

 reaction. A healthy cabbage seedling was planted in each pot, and 

 at the end of two months the plant in the pot containing lime was 

 perfectly healthy, whereas the plant in the soil containing acid bone 

 manure was badly diseased. 



6. Two pots containing soil mixed with quicklime and acid bone 

 manure respectively had a diseased cabbage seedling placed in each. 

 At the end of two months the disease was more developed in both 

 seedlings than at the time of planting ; proving that the presence of 

 lime will not arrest the disease when the plants are once attacked. 



Summary. 



The foregoing observations and experiments demonstrate the 

 following points : 



1. That in addition to cultivated plants, several common weeds 

 belonging to the order Cruciferce are attacked by the Plasmodiophora. 

 Hence the necessity for preventing the growth of such weeds in fields 

 and hedge- banks. 



2. That the germs of disease are present in soil that has produced a 

 diseased crop, and retain their vitality for at least two years. 



3. That the development of Plasmodiophora is favoured by the 

 presence of acids, and checked by the presence of alkalies, agreeing in 

 this respect with the fungi rather than with bacteria. 



4. For the purpose of sterilising infected soil, experiments prove 

 that either a dressing of lime or a manure containing potash salts is- 

 effective, the last being most valuable, as it not only destroys the 

 germs in the soil but also arrests the disease in seedling plants, and 

 at the same time supplies one of the ingredients necessary for the 

 healthy growth of turnips. 



Presents, February 14, 1895. 

 Transactions. 



Baltimore: Johns Hopkins University. Circulars. Vol. XIV. 



No. 116. 4to. Baltimore 1895. The University. 



Berlin:- Gesellschaft fur Erdkunde. Verhandlungen. Band 



XXI. No. 1. 8vo. Berlin 1895. The Society. 



Boston : Society of Natural History. Memoirs. Vol. III. No, 



14. 4to. Boston 1894; Proceedings. Vol. XXVI. Parts 



2, 3. 8vo. Boston 1894; Occasional Papers. No. 4. 8vo. 



Boston 1894. The Society. 



