CONTRIBUTIONS FROM THE WISLEY LABORATORY. 



383 



Table I. — (continued). 

 Variety. Source of Seed, etc. 



10. Langworthy . . . Purchased from another source. 



11. Sutton's Abundance . . „ ,, „ „ 



(Bishop Auckland, 1908; seed from these grown 



12. British Queen . . .J partly in Devon and partly in Newcastle, 1909 



[ seed from these planted at Cleadon, 1910. 

 13 Un-to Date 1 ( 1^^^^^^' ^^^^ ' Cleadon, 1909 ; selected tubers 



14* Dalhousie J ' ' ] through the winter at Newcastle and planted 



/ Dunbar, 1908 ; Cleadon, 1909 ; selected tuberg left 

 in the soil of the farm and others in the manure 

 15. Up-to-Date and Dalhousie . A ^gg^ ^^xe farm through the winter, and planted 



( 1910. 



In 1910 the loss occasioned through Fhytoplithora-was shght, but 

 a " new " disease — potato canker — manifested itself. This disease 

 was first detected towards the middle of September, when some plants 

 of the variety ' King Edward VII.' were lifted and found to exhibit 

 incipient stages of canker. Thinking that the disease might be con- 

 fined to this variety, it was decided to dig up all the tubers and remove 

 them from the soil at once. Soon afterwards, however, it was dis- 

 covered that not only were the remaining experimental rows attacked, 

 but that the main crop was slightly affected, so that it was not possible 

 to eradicate the disease. The potatos were lifted by the middle of 

 October, and by this time the reproductive bodies of the parasite had 

 been formed, which, falling from the diseased tubers, remained to 

 infect the soil. 



It is perfectly clear that the parasite was not introduced on the 

 land— which was uniformly infected — in 1910 by means of infected 

 seed, since the seed came from several different sources (as shown by 

 the table) and was carefully examined; moreover, tubers from every 

 sample grown at Cleadon were planted in the Armstrong College 

 garden, and others, from a few samples, were sent to Devonshire, 

 but not a single case of canker occurred in those places. 



I am indebted to Dr. W. G. Smith, of the East of Scotland 

 , College of Agriculture, for permission to visit the experimental plots at 

 Prestonpans, where trials were being made of potatos of a given 

 variety grown in different districts in the previous year. All the 

 rows were equally affected, but very slightly, with Spongospora. The 

 varieties of potato and the localities from which the seed was obtained 

 are given in the following table of the additional cases of the occur- 

 rence of canker : — 



Table II. 



Variety. Remarks. 



Grown at Dunbar ; farmyard and airtificial manure 

 1. Navarre . . . . | used. Kotation : potatos, wheat, hay, potatos, 



turnips, barley, potatos. 



Langworthy — 



(1) Seed from Boon. 



(2) Seed from Midlothian. 

 Up-to-Date — 



(1) Seed from East Lothian. 



(2) Seed from Leadburn. 



(3) Seed from Boon. 



(4) Seed from Banffshire 



(coast). 



Grown at Prestonpans ; all slightly affected ; 

 artificial manure used. Kotation : barley, hay, 

 oats, ipotatos. 



