4 



The diluted lime-sulphur wash, which is a perfectly clear liquid, 

 should be applied with a nozzle throwing a very fine "misty" 

 spray. The same type of nozzle which is suitable for the appli- 

 cation of Bordeaux mixture (see this Journal for January last) is 

 suitable for the lime-sulphur wash. The receptacle of the spraying 

 machine must be wooden or iron (galvanised iron or tin) ; a copper 

 knapsack sprayer must not be used, as the wash acts chemically 

 on this metal. Knapsack sprayers which are tinned over can be 

 obtained. According to the results of experiments recently carried 

 out in the United States, certain arsenical washes can be added 

 to the lime-sulphur wash. 



M. C. POTTER. On a Method of checking Parasitic Diseases 

 in Plants. Journ. of Agr. Science, Vol. Ill, PI. i, pp. 102-107, 

 Dec. 1909. Cambridge. 



In the study of the action of bacteria in pathogenic relation to 

 the higher plants various types of bacterial diseases have been 

 established. 



One large class comprises those in which the bacteria invade 

 the cells of the parenchyma, producing a rapid degeneration of the 

 cell and its contents and complete destruction of the tissues. To 

 this group belongs the "White rot" of the turnip, caused by 

 Pseudomonas destructans (Potter). This bacterium secretes an en- 

 zyme (cytase) which acts on cellulose, swelling and disintegrating 

 the cell walls; while at the same time producing a toxin fatal to 

 the protoplasm of its host cell. Its action extends rapidly from 

 cell to cell, the entire parenchymatous tissue becomes speedily re- 

 duced to a watery pulp. 



Pseudomonas destructans, both when growing upon the turnip 

 and also in a nutrient solution produces a substance, toxic to 

 the living plant cell, which retains this property after boiling ; the 

 cytase on the contrary being destroyed by the high temperature. 



The toxine thus separated from the cytose is toxic to the 

 Pseudomonas and this has been demonstrated on turnips cut in 

 halves and artificially inoculated with pure culture of P. destructans, 

 and then treated with the toxin. 



In the treated halves the decaying areas did not increase and 

 the disease was completely arrested, whilst the untreated halves 

 gradually became completely rotten. 



This toxic solution prepared from the turnip is not necessarily 



