[ 6-'3 ] 



VII. 



THE VERTICILLIUM DISEASE OF THE POTATO. 



By GEORGE H. PETHYBFJDGE, Ph.D., B.Sc, 



Economic Botanist to the Department of Agriculture and Technical 

 Instruction for Ireland. 



(Plates 1I-III.) 



[Read December 21, 1915. Published March 22, 1916.] 



I. Introductory. 



During the past seven summers special investigations dealing with various 

 diseases of the potato have been pursued in Ireland, where the potato crop is 

 such an important one. Some of the diseases dealt with have been new, 

 while others, although not new, were more or less obscure and had previously 

 been insufficiently studied, so that it was possible to throw new light on 

 them. 



The results of these investigations have been published annually in the 

 form of general summaries or reports, and in certain eases the diseases have 

 formed the subjects of special scientific papers. 1 



The disease with which the present paper deals has been referred to 

 briefly in these reports from 1910 onwards, but no detailed account of it has 

 yet been given. It is not really a new disease, although up to the time of 

 starting the present investigations comparatively little was known about it, 

 and definite record of its presence in the British Isles had apparently not 

 been made. It has, in fact, long remained incompletely studied and concealed 

 amongst the congeries of diseases passing under the names of Curl and Leaf- 

 Roll, from which, however, it must now be removed and be recognized as a 

 distinct disease of a definite type caused by a specific parasitic organism, as 

 will be clear from the discussion in Section VIII of this paper. 



The reason why the present study of the disease has been a somewhat 

 protracted one is partly because the disease was only one of several which 



1 These reports will be found in the Journal of the Department of Agriculture and 

 Technical Instruction for Ireland, vols, x, xi, xii, xiii, xiv, and xv, 1910 to 1915. 

 References to the special scientific papers mentioned will be found in these reports. 



SOIENT. PKOC. K.D.S., VOL. XV, NO. VII. L 



