TRANSACTIONS OP SUB-SECTION K. .603 



the Department of Agriculture and Technical Instruction, it has been found pos- 

 sible to disentangle from a congeries of diseases, formerly somewhat indefinitely 

 described under the name of ' yellow blight,' a definite bacterial disease of the 

 potato to which the name of ' Black Stalk Rot ' has been given. The disease 

 resembles the 'Black Leg,' ' Schwarzbeinigkeit,' &c, of other authors, and is 

 caused by an organism which is not absolutely identical with any of those 

 hitherto described, and which has been named Bacillus melanogenes. The main 

 symptoms of the disease are a wilting and yellowing of the foliage, a degeneration 

 of the vascular bundles of the stalks, and decay of their subterranean portions 

 and of the tubers. The disease is apparently spread chiefly by the planting of 

 affected tubers, which are not easily recognised as such. Its importance consists 

 not only in the fact that plants are killed in the field by the organism, but also 

 in that the latter produces a most serious rot in stored potatoes, even healthy 

 unwounded tubers being capable of infection through their lenticels when in 

 contact with diseased material. Preventive measures should aim at the destruc- 

 tion of attacked plants in the field, the total exclusion of affected tubers from 

 pits and clamps, so far as this is possible, and the construction of the pit and 

 clamp in such a way that the conditions favourable to the development of the 

 organism (moisture and warmth) are not present. 



(iv) Potato Disease. By A. S. Horne, B.Sc, F.G.S. 

 This paper dealt with the following topics : — 



The power of the cell of the potato tuber to respond to altered physiological 

 conditions: (a) under certain circumstances storage cells assimilate; (b) storage 

 cells may be modified in connection with the formation of intumescences ; (c) they 

 may become meristematic ; and (d) the effect of over stimulation. 



The potato plant relative to its environment : (a) artificial stimulation of 

 germinating tubers; (b) the experiments of Raoul Combes; (c) various experL 

 ments. 



The probability that a plant will thrive in a given spot depends upon cer- 

 tain combinations of factors. These may be conveniently grouped as follows : — 



(1) Factors relating to structure and internal constitution of the plant, 



and to the organisms intimately associated with it. 



(2) Factors relating to the soil and organisms present in the soil. 



(3) Factors relating to the climate and season, and to aerially borne organ- 



isms. 



Disease may occur if the optimum arrangement of factors be disturbed. 

 The experimental production of soft rot (Nassfaule) in the laboratory. The 

 artificial production of 'Leaf Blotch' and probable explanation of this disease. 

 The phenomena attending ' Leaf Curl ' and ' Leaf Roll ' (Blattrollkrankheit). 

 ' Black-leg ' in potato. The importance of arriving at a correct and full know- 

 ledge of the life-history of potato pests, with special reference to Phytophthora 

 infestans and Spont/ospora solani. Local epidemics of Spotujospora in 1910. 

 Internal disease of potato. Potato breeding in relation to plant pathology. 



(v) A Bacterial Disease of the Potato Plant. By Miss E. Dale. 



2. The Influence of Electricity on Micro-organisms. By J. H. Priestley 



and Miss E. M. Lee. 



This paper dealt with the investigation of the effect of weak currents of 

 electricity upon micro-organisms, using the rate of production of their metabolic 

 products as an index of their rate of growth. 



The organisms selected as the result of many preliminary trials were 

 B. Bulgari* us, the 'sour milk' bacillus of Professor Metchnikoff. A very active 

 strain, producing 14 per cent, of lactic acid in ten hours, was procured, and pure 

 cultures were used throughout the work. 



Milk cultures of the bacillus were set up in Kohlrausch electrolytic cells and 



