Pethybjiidge and Murphy — Bacterial Disease nf the Potato. 19 



semi-liquid pulp. Since no very special precautions were taken in this par- 

 ticular instance to select the inoculating material from a position in close and 

 direct proximity to the still healthy tissue, our non-success is easily understood. 

 Unfortunately whilst the isolation experiments from this tuber were in 

 progress, and before we had realized our failure to obtain the pathogenic 

 organism from it, the tuber itself was discarded, so that a fresh attempt with 

 the same tuber was rendered impossible. There is little doubt, however, that 

 the tuber had been primarily attacked by the organism in question, especially 

 in view of the fact that one of the successful isolations mentioned above was 

 made from a diseased tuber borne by the same plant. 



An attempt was also made to isolate the organism from the soil, but with- 

 out success. Infection-experiments carried out with the organisms isolated in 

 pure culture from the soil gave nothing but negative results. This disposes of 

 the view recently brought forward by Hegyi,^ without sufficient experimental 

 evidence, that any or all of the common soil organisms may cause the disease 

 by effecting an entrance into the portions of the stalks below ground through 

 wounds caused by insects or other animals. 



The soil of the particular plot in question — reclaimed bog — had not, it is 

 true, given any indications during the previous season of being infested with 

 any organism toxic to the potato plant ; but in it had been planted a large 

 number of tubers which were known to have been derived from plants which, 

 during the previous season, had suffered badly from Black Stalk-rot. As a 

 consequence, the plants arising from these tubers were, to the extent of 

 ninety-four per cent., attacked with this disease during the summer ; and as a 

 matter of fact the sample taken for isolation purposes was selected from a 

 spot rather near a rotting tuber borne by one of these plants. Nevertheless 

 the organism was not obtained. This particular plot has now been enriched 

 by the addition to it of a number of tubers and stalks affected with the disease; 

 and it will be interesting to observe next year whether plants derived from 

 perfectly sound tubers of known origin, which it is intended to plant in it, will 

 become diseased. A fresh opportunity will then be afforded of ascertaining 

 whether the organism is present in that soil or not. 



Again, an endeavour was made to obtain the organism from the stalks of 

 affected plants of the previous season, which had been allowed to become air- 

 dry, and which had been hanging up in a bundle in the laboratory for a period 

 of about ten months. In this case also we were not successful. It is true we 

 have never observed the formation of spores by this organism ; Imt we have at 

 present no certain knowledge of its powers of resistance to dessication, and too 

 much stress must not be laid on the negative results given by a single experiment. 



' Zeitsulirift i'iir Pflanzeukrankheiten, xx. 1910, p. TO. 



I a 2] 



