214 Scientific Proceedings, Royal Dublin Society. 



and uninjured eyes. In one case a sprout of about 1 cm. long became infected 

 at its uninjured tip, and the fungus passed back through this sprout, killing 

 it, and eventually reaching the tissue of the tuber. In five other cases sprouts 

 became similarly infected, but at the conclusion of the experiment the 

 decay had not extended from them to the tuber. 



It is, therefore, clear that although this fungus is, perhaps, most frequently 

 a wound-parasite, yet, under favourable conditions, it can attack uninjured 

 tubers through lenticels, eyes, or young sprouts. 



Pesults of Planting Infected Tubers.— Nearly every season we have brought 

 to our notice one or more cases where early potatoes have failed to make a 

 stand, or have made only a very bad one. Almost invariably these have 

 been cases in which cut sets were planted, which were found when dug up 

 to be seriously decayed with dry-rot. In such cases of course it is impossible 

 to say after the event whether the seed tubers used were at fault, or whether 

 the sets became infected from the soil, subsequent to planting. 



In order to ascertain what happens when naturally infected whole tubers 

 are planted, nine such tubers, ascertained to be infected with F. cceruleum, 

 were planted in pots of soil in an unheated greenhouse. Healthy tubers 

 were planted in pots of similar soil for purposes of comparison. Three of the 

 infected tubers rotted completely in the soil and gave rise to no plants. The 

 other six produced small plants, which remained perfectly healthy, died off 

 eventually in a natural way, and in post-mortem examination showed no 

 evidence of attack by F. cceruleum, or other organism. 



Four tubers artificially inoculated with the fungus were also planted 

 after the rot had become well established., All four produced small, healthy 

 plants, which died off naturally, and no traces of the fungus could be found 

 in them on subsequent microscopical examination. 



It is our experience that if, when planted, a tuber is already seriously 

 decayed with dry-rot, and particularly if the decay is in close proximity to 

 the eyes or sprouts, the probability is that no plant will be produced. If, 

 however, when the tuber is planted the amount of decay is slight, or is not 

 in the immediate neighbourhood of the eyes or sprouts, the latter have 

 time to grow and produce overground shoots having their own roots; and 

 these shoots do not subsequently become invaded by the fungus. 



Does F. cceruleum cause a Disease of the Potato Plant as a whole, or only a 

 Pot of the Tuber ? — If this fungus were capable of attacking the roots of the 

 potato plant, and of thus killing it, we should have expected this to happen 

 when either naturally or artificially infected tubers were planted. It would 

 seem almost certain that under such conditions the roots on the underground 

 portions of the stalks would be exposed to infection by contact with the 



