19-20.] 



The Distribution of Wart Disease. 



735 



host plants without being noticeable, or if it completed its life 

 cycle in the soil as a soil organism without attacking any plant, 

 the varieties of potato then cultivated m.ust have possessed 

 the characters of immunity from the disease — or that the fungus 

 only acclimatised itself to live on these potatoes at a later date — 

 but that, as these old resistant varieties were displaced by newer 

 kinds, the fungus, finding in the new^er varieties suitable hosts, 

 gradually adapted itself to these and commenced a period of 

 its life on the potato. 



If, on the other hand, S. endohioticum is not indigenous, how 

 was it introduced into this country? It is hardly possible that 

 it could have been brought with the original potato from South 

 America, as all the varieties from Chili which have been tested 

 have been found to be immune, and in any case, if the disease 

 had been introduced with the original potato, it is probable that 

 the fungus would have made itself evident at a much earlier 

 date, both in this country and in Germany, Spain, Austria and 

 Belgium. 



Tt is a matter of common belief in certain districts that Wart 

 Disease was introduced into this country (with potatoes) from 

 Germany, but there is little evidence in support of this state- 

 ment. Wart Disease is present in Germany to a limited extent. 

 Tt is found chiefly in West Germany (Ehine Provinces), and to 

 some extent near Hamburg, and in Holstein. There are scat- 

 tered cases elsewhere, but there is no evidence that it has been 

 prevalent in the fields until recent years. All the available 

 records go to prove that Wart Disease is more prevalent in the 

 R^'it^'sh Isles than elsewhere. 



Early History of Disease. — Many oardeners and farmers in 

 Lancashire and Cheshire have stated that Wart Disease w^as 

 present in England in the 'seventies, and a number of people 

 appear to have recognised it about that time. 



It is not always wise to accept statements as to the presence 

 of a disease many years 'before, unless the statements can be 

 supported by facts. Wart Disease, however, is so characteristic, 

 and is so different in appearance from other potato diseases, that 

 more value than usual may be placed on the truth of these state- 

 ments. If the statements are correct, it means that long before 

 the scientific world knev>^ of the existence of this disease, it had 

 probably firmly established itself in cottage gardens in Lanca- 

 shire, Cheshire and Shropshire, in North Wales, and in certain 

 parts of the South of Scotland. 



