310 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



got into these its spread was much more rapid. Even then it was not 

 so rapid as now, for, speaking generally, the farmer who got infected 

 " seed " only had isolated infected plants, and with a four-year rotation 

 it was eight or twelve years before the disease would attract serious 

 attention, and he would continue to supply local growers without 

 spreading infection to any extent. Of recent years, what with the 

 increased infection of fields, both in England and Scotland, and the 

 greatly increased demand for change of " seed," especially from 

 the North, where it is worst, Wart Disease has had every opportunity 

 for dissemination. During the war,- when the usual methods of 

 transport were upset, and especially in the spring of 1917, when there 

 was a shortage of both " seed " and ware potatos, not only did " seed " 

 potatos come from infected districts into clean, but potatos from 

 infected districts were used for " seed," and this increased the number 

 of infections in the South, which hitherto had been exceptionally 

 free. 



Extent of the Disease. 



The disease has now been recorded from every county in England 

 except Suffolk and Cornwall, but East Anglia and Lincolnshire have 

 few cases, and the South of England generally is but slightly infected. 

 The Midlands, north-western counties, and Wales are badly infected. 

 Scotland has a considerable amount of the disease, especially in Mid- 

 Scotland and the South, but the northern counties appear to be free. 

 Ireland is free but for a small district in the southern part of County 

 Down. Its presence on the Continent and in America has already 

 been mentioned. 



Future of the Disease and the Potato Industry. 



The present extent of the disease and the fact that, notwith- 

 standing the efforts of the Ministry of Agriculture, the fungus is 

 obviously spreading, show that the future of the potato industry is 

 imperilled. Thousands of acres are infected, not necessarily badly, 

 although there are scores of 'fields where a profitable crop of susceptible 

 varieties cannot be grown, and it is only a question of a few years 

 before all are so infected with sporangia that they will be useless for 

 the growing of what are now the popular varieties. With no remedy 

 to hand at present — and if there were, the probability is that it could 

 not be supplied in sufficiently large quantities to eradicate the fungus — 

 it is obvious that the breeding and selection of immune varieties 

 must be continued, so that the present susceptible varieties will 

 gradually die out and be replaced by those that prove immune. Up 

 to the present no variety which has been certified as immune by the 

 Ministry of Agriculture has taken the disease, the reported cases when 

 investigated having been proved to be " rogues " or wrongly named 

 varieties. As both in England and German)' (72) reinfection of the 

 potato occurs at least nine years after the last crop of potatos, not only 



