CONTRIBUTIONS FROM THE WISLEY LABORATORY. 



385 



peculiar distribution of Spongospora have been reported from gardens, 

 but the information available is too indefinite to be of service. It is 

 by no means an unusual experience in potato fields where a regular 

 rotation takes place to find that a particular disease — known to occur 

 upon the fields used for potato-growing — which was prevalent in one 

 year does not appear, or not to any extent, on the same farm in the 

 following year. This happened in connexion with Pliytoplitlionv at 

 Cleadon, but the seasonal conditions in this district in 1909 differed 

 from those obtaining in 1910. It is a common experience witn 

 " Sprain." Thus a number of factors would have to be considered 

 before it could be stated that Spongospora does not exist upon a par- 

 ticular field or farm. The above-mentioned observations emphasize the 

 importance of exercising a considerable amount of caution in the inter- 

 pretation of the results of field experiments carried out over a limited 

 period of time within a limited area. 



The use of lime has been advocated as a remedy for the disease, 

 and in Mas see's Diseases of Cultivated Plants and Trees the following 

 advice is given: "Infected land should be dressed with quicklime, 

 preferably in the spring, when the spore-balls are germinating in the 

 soil." The experimental rows at Oleadon extended twenty-eight yards 

 down the field, and these received a light dressing of lime fourteen 

 yards down, so that half the quantity of each variety was planted in 

 limed, the other half in unlimed, soil. In some cases liming the soil 

 appeared to have a beneficial effect upon the foliage, but in almost 

 every instance it brought about an increase in the amount of disease. 

 A similar result was obtained by G. H. Pethybridge in experiments 

 conducted at Glifden, and near Belmullet, in Ireland. 



[I wish to express my thanks to Professor J. B. Farmer, F.E.S., 

 and to Mr. F. J. Chittenden, F.L.S., for valuable advice and criticisms 

 in connexion with thifs paper. I 'also desire to acknowledge my 

 indebtedness to the Eoyal Society for help from a Government Grant 

 in aid of the investigation of the more obscure diseases of the potato. ] 



Summary OF Observations. 



1. The field crop and a number of experimental rows of potatos 

 grown at Cleadon in 1910 were affected v/ith potato canker. It is 

 extremely improbable that the disease in this case was introduced by 

 infected seed in 1910, for the following reasons: — 



(a) The seed had been derived from several different known 

 sources. 



(b) The potatos planted in the experimental rows had been care- 

 fully selected. 



(c) The land was found to be uniformly infected. 



2. A particular variety, the 'King Edward VII.,' was badly 

 diseased in some districts but only slightly affected, or not at all, in 

 >thers, although other varieties in the same fields were diseased. 



VOL. XXXVII. C C 



