A. S. HoRNE 201 



For this reason the percentage of bad plants obtained through a 

 particular stock of the President might be greater than that obtained 

 through the use of another stock and the total yield proportionally less- 

 other conditions being similar. 



Canker. 



Owing to the serious notice given to potato canker, in a recent 

 Bulletin issued by the United States Department of Agriculture, 

 investigators in Great Britain may be compelled to devote considerable 

 attention to this disease, although as already pointed out by the writer, 

 the worst cases in this country are to be found in ill-kept gardens, whilst 

 comparatively little damage is done to the potato harvest by canker. 

 The tubers in the field crops are sometimes scabby but the scab is often 

 less noticeable than the brown scab of unknown origin prevalent in 

 many parts of the country. I. E, Melhus^, the author of the United 

 States Bulletin, devotes little attention to the comparatively trivial 

 damage caused by the canker organism in Britain whilst prominence 

 is given to the statements of serious damage to the potatoes in Ireland. 



In Ireland canker is reported as causing considerable loss to the 

 potato crop. Johnson^ states " I have no doubt myself, that this Spongo- 

 spora scab has a good deal to do with the miserable average yield per 

 acre of potatoes in the west of Ireland. It is in some districts of Ireland 

 as injurious to potatoes as finger-and-toe in Turnips," and Pethybridge^ 

 writes of the attacks caused by Spongospora, " they were particularly 

 disastrous on those portions of the land which for special purposes have 

 now been cropped for four successive seasons with potatoes, the can- 

 kerous form of the disease being extremely common." 



GUssow* with regard to canker in Canada states " the disease should 

 by no means be regarded lightly. Severe attacks occur when potatoes 

 are planted year after year in infected land." The disease was also 

 regarded seriously by Pole-Evans, in a circular issued by the Transvaal 

 Department of Agriculture in 1910. 



Pethybridge and Giissow specially note the occurrence of canker in 

 land that has been cropped year after year for potatoes and it seems 

 clear, from the published accounts of its occurrence in Ireland, that the 



1 I. E. Melhus in U.S. Dept. Agric. Bur. PI. Ind. Bull., No. 82 (April 6, 1914). 



2 T. Johnson in Econ. Proc. Roy. Dub. Soc, l (1908), p. 453. 



^ G. H. Pethybridge in Jour. Dept. Africa. Tech. Instnic. Ireland, x\n. No. 3 (1913); 

 p. IG. 



■* H. 'I\ Giissow in Phytopathology, V, 3, No. 1. 



