182 



INJURIOUS INSECTS AND FUNGI. 



[Sept.. 1895. 



" Summary. 



" The foregoing observations and experiments demonstrate 

 the following points : — 



" 1. That in addition to cultivated i:>lants, several common 

 weeds belonging to the order Griiciferce are attacked by the 

 Plasmodiophora. Hence the necessity for preventing the 

 grov^^th 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 Jast 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." 



The practical outcome of the various experiments that have 

 been carried out in connexion with club root up to this date is 

 that infection may be diminished both by precautionary and by 

 remedial measures. The first of these include the destruction of 

 diseased roots as far as possible, the prevention of the transport 

 of the germs by carts and horses, the suppression of cruciferous 

 weeds liable to be attacked by this fungus, and caut'on in the 

 use of acid manures. The remedy consists in the application, in 

 proper quantities, of lime and of potash, which appear to have 

 considerable influence upon the progress of the fungus. 



