A. S. HoRNK 203 



has been up to the present in Europe, it would be rated as a disease of 

 secondary importance as compared with late-blight or with Fusarium 

 wilt. But there are reasons for fearing that it may become more pre- 

 valent here It quite often occurs that introduced parasites are more 



destructive in a new habitat than in their native environment. Likewise 

 it is not impossible that Spongospora may find the American varieties 

 of potato more susceptible than the European sorts." 



The prevalence of canker in many European countries and the 

 Dominion of Canada has prompted the Department of Agriculture in 

 the United States to extend for a time the Quarantine on foreign potatoes. 

 The attitude of the United States in this matter may render it advisable 

 to ascertain the distribution of canker in Britain as in the case of the 

 tumour parasite, but statistics would be difficult to obtain and the process 

 of recording would need to be spread over several years for numerous 

 and obvious reasons. 



The symptoms of canker have already been fully described by the 

 writer^. The organism Spongosjjora solcmi Brunchorst, as in the case 

 of Chrysophlyctis, can rest in the soil and there seems little immediate 

 prospect of arriving at a soil remedy. Both organisms form resting 

 bodies which are said to be capable of remaining for many years in the 

 soil, but whether there is any other mode of subterranean existence is 

 as yet quite unknown. Neither is it known exactly how the process of 

 infection is carried out, whilst we are almost entirely ignorant of the 

 conditions that favour or inhibit infection. 



Some varieties of potato, which are more susceptible than others 

 in a certain district, in other districts may be almost immune. There- 

 fore generalisations from experiments in one locahty only should be 

 avoided and tests established at several experimental stations. 



^ A. S. Home in Jour. Roy. Hort. Soc. xxxvii (1911). 



Ann. Biol. i. 14 



