532 Scientific Proceedings^ Royal Dublin Society. 



On the other hand, it is practically certain that Bhizoctonia violacea Tul. is 

 an actual parasite of the potato tuber. It is present on and in tubers which 

 in the west of Ireland are said to be suffering from "moss-burning," a kind of 

 rot proceeding from without inwards ; and although absolutely convincing 

 evidence has still to be obtained from inoculation with pure cultures, yet from 

 the penetration of the mycelium through the skin of the tubers by means of 

 the so-called corps miliaires, and from its copious growth within and the 

 accompanying collapse of the tissues, there can be little doubt of its parasitic 

 nature. 



Frank (9a) credited the fungus which he provisionally named PheUomyces 

 sclerotiophonis with the power of causing a rot iu potato tubers ; but the 

 investigations of Appel and Laubert (1), who discovered that the fungus was 

 identical with Spondylocladium atromrens Harz., show that this is not the case, 

 and that under ordinary circumstances this fungus is not capable of invading 

 the healthy tissues of potatoes, nor has it any serious significance as an agent 

 in the destruction of the tubers. 



Potato tubers are found not infrequently iu which more or less localized 

 portions of the internal tissues are seen to be browned and the cells dead, 

 although the affected tubers themselves often (but not always) appear 

 externally to be perfectly healthy ; and they can scarcely be said to undergo 

 rotting. This trouble has received various trivial names, such as " Sprain," 

 " Internal Disease," " Streak," " Eisenflecldgkeit," " Buntioevden" " Maladie 

 des Taches en Couronne," " Sulirose," &c. ; and it is, of course, possible that it 

 is not always of exactly the same nature or due to the same cause. 

 Swellengrebel (26) maintains that certain common soil bacteria are 

 responsible for this disease, or for one form of it ; but it must be confessed 

 that the evidence which he brings forward in support of his view is not 

 very convincing. Home (14) claimed to have discovered a parasite associated 

 with " Internal Disease," which he provisionally regarded as a Chytridiaceous 

 fungus of new generic rank ; but it is highly improbable that the bodies 

 which he described were indeed organisms of any kind. The majority of 

 investigators who have studied this disease have failed entirely to find any 

 organisms associated with it; and it is generally regarded as being due to 

 some physiological disturbance iu the tissues of an unknown nature. 



The present paper deals with a new and highly characteristic type of 

 tuber-rot which occurs in Ireland (and which will probably be found to occur 

 elsewhere), caused by a new species of fungus closely allied to that causing the 

 ordinary blight of tlie Fotsito, Phi/top/ithora infestaus, and yet differing in certain 

 important essentials from the latter. It was first observed in 1909, in the plots at 



