16 Proceedings of the Royal Irish Academy. 



In the first series of isolations a immber of diseased plants, ten in aU, 

 were plated from during the conrse of as many days. The material for the 

 platings was nsnally ohtained at a point where the diseased and healthy tissues 

 met in the pith of the stalks of affected plants which had been carefully 

 opened by a longitudinal cut with a sterile knife. In some cases the tissues 

 here were rather black and dry: in others they were soft, greenish, and 

 somewhat pulpy. In one case the material was obtained fi-om a discoloured 

 vascular bundle at a considerable distance up the stalk, where it was 

 completely surrounded by apparently healthy tissue. In most of these eases 

 a rough test of the toxicity of the pulp was made at the same time as the 

 platings were carried out by placing a little of it direct on sUees of living 

 potatoes (with controls) in Petri dishes, when a characteristic rot was found 

 to develop in them- 



In all cases the plates showed after a period of about forty-eight hours at 

 laboratory temperature a varying number of colonies according to the dilution 

 employed. After a further period of twenty-four houi-s it was clear that, in 

 all cases except one, liquefying oiganisnis were in great preponderance, Ijeing 

 accompanied by only a few colonies of non-liquefiers. The colonies of 

 liquefiers were, as far as could be seen with the naked eye, lens, and micro- 

 scope, all of one type, and consisted of actively motile, rod-shaped organisms 

 of varying length. Xot a single colony displaying gi-een fluorescence was 

 observed during these platings; but in other platings made later, on one or two 

 occasions em isolated colony having this characteristic did appear. Although 

 repeated attempts were made to cause a rot in potato-tubers with this 

 fluorescent organism, not the slightest success was met with : and we are veiy 

 doubtful whether the patht^enic characters ascribed to this type of organism 

 are really possessed by it. 



Before replating from the colonies which had developed from the first 

 series of plates, pi-eliminaiy tests were made as to the pathogenicity of the 

 organisms in them by inoculations made in a manner presently to be 

 described into fresh, young, living potatoes. In the case of the liquefiers rot 

 was set up in all instances : but with the non-liquefiers this was so in some 

 instances, and not in others. Particular attention was then paid to these non- 

 liquefying colonies since the organisms isolated, both by Smith (5. solanacearv/m), 

 and Delacroix {B. sol/iyiincoJa), ai'e described as being non-liquefiers : and we 

 considered that we might possibly have before us toxic forms of both liquefying 

 and non-Kquefying kinds. In every single instance, however, where inoculation 

 from an apparently non-liquefying colony produced a rot in the potato tuber, 

 it was found, on further culture, from the original colony that this was not 

 pure, but consisted of a mixture of hquetiers and non-Uquefiers. When, after 



