218 Scientific Proceedings, Royal Dublin Society. 



know for certain the source from which the infection primarily comes, it is 

 not easy to suggest preventive measures. Presumably the fungus is a 

 normal inhabitant of the soil, but research on this point is much needed. 



Other Species of Fusarium. F. arthrosporioides, &c— In addition to isolating 

 and cultivating the various strains of F. cceruleum as described above, a very 

 considerable amount of time has also been devoted to the study of other 

 species of Fusarium, principally F. Solani (Mart, pro parte) A. & W., F. Martii 

 A. & W., F. discolor A. & W. var. sulphureum (Schlecht.j A. & "W., and F. 

 trichothecioides A. & W. Strains of the first three species were obtained from 

 the Central Bureau in Amsterdam, while the fourth was kindly supplied by 

 the U.S.A. Bureau of Plant Industry. 



In some respects F. Solani and F. Martii resemble F. cceruleum, but they 

 both differ from the latter in the essential point that they are non-pathogenic 

 to the potato tuber. We were unable in spite of repeated trials to produce a 

 rot in tubers by inoculating with F. discolor var. sulphureum — a species which 

 other authors have found to be pathogenic to potatoes. Possibly the strain 

 used had lost its pathogenic character, owing to prolonged saprophytic 

 culture. 



With F. trichothecioides, however, a dry-rot of potato tubers was readily 

 produced. The form of rot caused by this fungus is somewhat different from 

 that caused by F. cceruleum. Characteristic of the cterideum-xoi is the 

 presence of comparatively few internal cavities which contain mycelium often 

 of a blue colour and relatively few conidia. The pustules which break through 

 the skin are compact and firm, and are blue at their bases. There is a faint 

 but pleasantly aromatic odour in the decaying tubers. In the case of 

 trichothecioides-Tot the attacked tissues are at first more spongy, owing to the 

 considerable development of cavities. The mycelium in these cavities is 

 never blue, and it bears an abundance of conidia. The external pustules are 

 more loose in texture, and there is no aromatic odour. These differences, 

 however, with the exception perhaps of the presence or absence of the blue 

 colouring matter, are scarcely well marked enough to make a differentiation 

 between the two kinds of rot an easy matter without having resort to 

 cultures. 



During the past three or four years in which our attention has been 

 specially directed to the matter we have never seen a case of natural 

 dry-rot in the potato tuber produced by any species of Fusarium other than 

 F. cceruleum, but further study and experience may possibly bring such to 

 light. We have, however, found at least one other species in this country 

 which has proved, on trial, to be pathogenic to potato tubers. A tuber of an 



