88 Scientific Proceedings, Royal Dublin Society. 



shows that the disease is characterized by the degeneration of the phloem 

 elements in the vascular tissue of affected plants, and he, therefore, uses the 

 term " phloem-necrosis " to describe it. What the exact cause of this lepto- 

 necrosis (as it might also possibly be termed) may be is not yet understood ; 

 but further investigation will, no doubt, yield interesting and possibly far- 

 reaching results. 



The conclusion as regards the Verticillium disease is, however, a clear 

 one, viz., that it is a specific disease caused by a definite parasitic fungus, 

 and, as such, it is not for the future to be classed under either of the some- 

 what indefinite terms " Curl " or " Leaf- Roll," but rather to be regarded 

 as a specific type of hadromycosis. 



IX. Distribution of the Disease, Losses caused by it, and Suggested 



Preventive Measures. 



The Verticillium disease of the potato seems to be fairly widespread on 

 the continent of Europe, and is present in the United States of America. It 

 is probably more or less prevalent in Great Britain, although, so far as I am 

 aware, no British mycologist has reported its presence there. 1 Marshall Ward 2 

 published many years ago a preliminary description of a disease which 

 very possibly may have been this particular one ; but apparently the matter 

 was never thoroughly investigated. Orton, 3 however, definitely states that he 

 obtained specimens of the disease in England from Ormskirk and Reading. 



Until the season of 1915, when two other cases of it came under my 

 notice, both of them in early potatoes of the variety Beauty of Hebron, the 

 only case of this disease which I had observed was the one found in 1909 and 

 propagated ever since then at the Clifden Investigation Station for purposes 

 of study. It should be stated that no special means have been taken to 

 ascertain to what extent exactly it may be prevalent in Ireland, and it may 

 possibly be commoner than one supposes. On the other hand, if it were 

 really common, and if it caused appreciable losses, it is most unlikely that its 

 presence in this country would have escaped the attention of the very 

 numerous agricultural Inspectors, Instructors, and Overseers who are in 

 such constant and close touch with our farmers. 



1 As has already been pointed out, the species mentioned in Miss Dale's paper was 

 probably not Verticillium albo-atrum, but some allied species. 



2 Ward, H. M., A Potato Disease. Rep. British Assoc, for Adv. of Science, 1898, 

 p. 1046. 



3 loc. cit, p. 87. 



