Pkthybkidgk ANn Mukphy — Bacterial Disease of the Potato. 15 



placed on the surface of a cut slice of the tuber. Apparently the drying up 

 of the potato-slices, and probably also the formation of a layer of protective 

 cork cells on their surfaces, were of influence in preventing infection from 

 taking place. For it was found that rotting was produced with more certainty 

 when the surface of the slice was cut in concave fashion, so that a little pool 

 of the inoculating fluid containing the pure culture could remain there for 

 some little time, and success was also rendered more certain when the 

 inoculating material was stabbed into the slice, instead of being merely laid 

 on its sui'face. On the whole, it was found easier to cause rotting in cut 

 portions of li-\dng stalks by stabbing into the pith than to produce it on slices 

 of tubers. The age and degree of ripeness of the tubers used would also 

 doubtless be of some influence, and this point will be referred to again later 

 on. 



Owing to the fact that a large amount of time had to be devoted to 

 diseases of the potato other than the Black Stalk-rot, it was impossible to 

 make any very great headway in the study of the organism causing the 

 disease during that summer; but the above-described investigations, although 

 of a preliminary and very incomplete nature, served well as a basis for 

 further work during the summer of 1910. During this latter period the 

 disease and its cause have been studied without interruption, from the end of 

 June up to the middle of October, the work being carried out as before at 

 the Temporary Station for the Investigation of Plant Diseases, at Clifden, 

 County G-alway. 



Care having been taken to ensure in the plots an adequate supply of 

 diseased plants, work was started on the re-isolation of the pathogenic 

 organism. The medium used for this purpose was potato-juice gelatine, made 

 at first strictly according to the directions laid down by Appel (5). It was 

 found, however, that a satisfactory potato-juice gelatine medium fulfilling 

 all our requirements could be prepared without having recourse to the 

 twenty-four hours' soaking of the tubers in strong soda solution, and also 

 omittmg the addition of citric acid before sterilization. It was not necessary 

 to have a gelatine of particularly high melting-point, since all our cultures in 

 this medium were kept merely at laboratory temperature which did not rise to 

 20° C. The medium as prepared was always rendered very shghtly alkaline, 

 the indicator used being litmus. We may state, however, that our experience 

 with the organism which we have isolated has shown that it has no very 

 strongly-marked predilection in favour of a gelatine medium prepared from 

 potato-juice ; and it grows almost equally well in a similar medium prepared 

 from Liebig's extract of meat with Witte's peptone, although perhaps in this 

 latter the rate of liquefaction is if anything very slightly less rapid. 



