210 Scientific Proceedings, Royal Dublin Society. 



cause of the rot by isolating it again from the decaying tubers. This was, 

 however, done in six cases, and the fungus obtained in pure culture in 

 each case. 



Pathogenicity towards Plants other than the Potato. — Attempts were made 

 to infect onions, mangels, carrots, parsnips, and apples with pure cultures of 

 F. cceruleum ; but the fungus proved itself to be non-pathogenic in these cases, 

 at least under the conditions of the experiments, which were similar to those 

 under which positive results were obtained with potato tubers. 



Similar trials were made with tomato fruits, the fungus being inoculated 

 through wounds made for the purpose. In both of two sets of experiments 

 positive results were obtained. The decay produced in the fruit is not 

 particularly rapid, only about one quarter of the inoculated fruit becoming 

 involved during the course of a fortnight. 



The surface of the decayed area becomes somewhat sunken and covered 

 with a layer of conidiophores bearing conidia which, in the mass, are of a 

 pinkish -cream colour. Cavities occur in the decayed tissue of the fruit, 

 which are more or less completely filled with white mycelium. The decayed 

 tissue is of a spongy consistency, and is thoroughly permeated with mycelium. 



From small portions of such diseased tissue, removed under aseptic 

 conditions and placed upon suitable media, the fungus was re-isolated in pure 

 culture, thus completing the proof that it was the cause of the decay. Control 

 fruits treated similarly to the inoculated ones, but not inoculated, remained 

 perfectly healthy. 



It is clear, therefore, that this fungus is pathogenic to the fruits of the 

 tomato provided wounds are present. Whether it can attack the uninjured 

 fruit or not we are not in a position to say. 



Influence of Maturity of the Tuber on the Susceptibility to Infection. — Some 

 of our infection experiments were made in the summer and early autumn, 

 and the results were more or less negative. Further trials soon aroused the 

 suspicion that the age or maturity of the tubers had a considerable influence 

 on the susceptibility to infection, and specific experiments were, therefore 

 carried out to ascertain whether the suspicion was well-founded or not. 



For this purpose tubers of the varieties " May Queen " and " Ninety-fold," 

 known to be susceptible, were used. It was found that one of the strains of 

 F. cceruleum when inoculated in the early summer into May Queen tubers of 

 the previous season produced dry-rot with ease and certainty," but that when 

 the same strain was used to inoculate tubers of the same variety newly dug 

 in July, the results were almost entirely negative. Hence a series of 

 periodic inoculations was carried out, the details and results of which are 

 summarized in the following table. The tubers used were specially grown 



