86 Scientific Proceedings, Royal Dublin Society. 



was then prevalent in Germany and some of the neighbouring countries. 

 The disease was stated to be by no means a new one, but rather one which 

 had hitherto been included amongst that congeries of diseases known as 

 " Curl " (Krauselkrankheit). To this particular form of disease the name 

 Blattrollkrankheit (" Leaf-Eoll " disease) was given, and one or more fungi 

 (not specifically named) belonging to the genus Fusarium were said to be 

 the cause of it. 



This publication may be looked upon as the first of a long series of others 

 which followed dealing with "Leaf-Eoll." In some of these Appel's results 

 are confirmed, and to some extent amplified. Thus, not only was a Fusarium 

 found to be the cause of the disease, but in many cases the parasite was found 

 to be Vcrticilliwm albo-atrum. 1 On the other hand, many students of the " Leaf- 

 Eoll " disease stoutly maintained that it was not due to a fungus at all, for the 

 simple reason that the presence of a fungus in the vessels (as described by 

 Appel) was by no means a constant or, in some cases, even frequent symptom 

 of the disease. Thus arose a controversy between those who regarded this 

 disease as of parasitic origin and those who maintained the contrary, 

 and who explained it as being due perhaps to the upsetting of enzymic 

 equilibrium, or some other such occult cause. It is not necessary to deal 

 here with the literature which this controversy brought into existence ; 

 suffice it to say that had the upholders of the non-fungus theory of the cause 

 of " Leaf-Eoll " been acute enough to realize that the disease with which they 

 were dealing was not the " Blattrollkrankheit " as first defined by Appel at 

 all, but something quite different, the controversy would probably never have 

 arisen. However, the development of this controversy need not be regarded 

 as having served no useful purpose, for it has certainly been the means of 

 stimulating research into some of the more obscure diseases of the potato, 

 from which good results have followed. 



It will be seen then that just as the term " Curl " is not applicable strictly to 

 any one specific disease, so the term "Leaf-Eoll," although introduced to apply 

 to the specific disease caused by species of Fusarium invading the wood 

 vessels, came to connote not only this disease, but also a similar one due to 

 Vtrticillium albo-atrwm, and, further, another (or possibly others, for the 

 matter cannot yet be regarded as definitely settled), the cause of which 

 is still not sufficiently well understood. 



A distinct step forward in the direction of a clearing up of the prevalent 

 confused ideas concerning Leaf-Eoll was the publication in 1914 of a 



1 Appel, O, " Einiges iiber die Blattrollkrankheit der Kartoftel. " Jahresber. Ver. 

 Angew, Bot., vi, 1909, p. 259. 



