Pethvbkidge and Murphy — Bacterial Disease of the Potato. 9 



was not noticed until after a period of thirty-five days ; but, in certain 

 other gelatine cultures, Hquefaetion set in very much earlier ; so that on the 

 whole the organism must rather be looked upon as a liquefier than a non- 

 liqxiefier. On raw potato the organism grows well, producing a softening and 

 maceration of the tissues, accompanied by the development of a brown or 

 black stain. Harrison presents an enormous mass of details concerning the 

 growth of the organism on media, both living and dead, of the most varied 

 kind, which need not concern us here. They will be dealt with when 

 necessary further on in this paper. 



From this summary, therefore, it will be seen that during the course of 

 the last twenty years bacterial diseases of the potato have been observed 

 widely distributed in various countries, both of the New and Old World ; and 

 no less than six organisms- pathogenic to the potato plant have been described, 

 more or less in detail, for all of which, with the possible exception of 

 B. caulivortcs, valid proof of pathogenicity has been supplied. 



With regard to Ireland the presence of one or more bacterial diseases of 

 the potato has been assumed for the past eight or nine years, the first intima- 

 tion of it having been given, as stated, by Delacroix ; but the matter has not 

 been closely inquired into. It was in order to clear up any uncertainty on 

 this point, and to obtain information as to the nature and cause of what 

 appeared to be a fairly widespread disease of this character, that the following 

 investigation was undertaken. The work was started by one of us in the 

 summer of 1909, and was continued and extended conjointly during the 

 summer of the present year in a small temporary laboratory (and on the plots 

 adjoining it) erected in the west of Ireland by the Department of Agriculture 

 and Technical Instruction for Ireland, for the purpose of studyuag the various 

 diseases to which the potato is subject there. It must not be supposed, 

 however, that this disease is by any means confined to the west of the country ; 

 it is prevalent to a greater or less extent in every part of the country 

 where potatoes are grown, and seems to be making itself more seriously 

 felt during each succeeding season. A preliminary description of the disease 

 was given by one of us early in the present year (23) ; and the following is a 

 more complete and detailed account of our present knowledge concerning the 

 disease and its cause. 



II. Chaeactees of the Disease. 



As mentioned previously, the disease in question has a good many 

 characters in common with the German " Schwarzbeinigkeit " or " black- 

 leggedness." Since, however, the term " Blackleg " is one which is already 



K.I. A. PEOC, VOL. XXIX., SECT. B. [B] 



