290 



with a very fine mycelium. The fungus liad consumed the cell- 

 contents, and thickened cell walls formed a corky layer, which 

 separated the diseased part from the healthy cells. He was 

 unable to obtain any fructifications or other characters to 

 determine the fungus present. He gives diagrammatic figures 

 of the external and internal characters of the " wart." In his 

 report for 1909, Carruthers again mentions the recurrence of this 

 particular form of scab, but makes no further comment. Though 

 the description is not very precise these records have usually 

 been regarded as referring to Skin Spot, and a note by Giissow, 



published last year, proved this assumption to be correct (see 

 below). 



In 1915, Pethybridge, in his Annual Report on Investigation 

 on Potato Diseases for 1914, gives (p. 35), a note on the occurrence 

 of the disease in Ireland, and proposes the name " Skin Spot." 

 He states it was characterised by the presence on the skin of the 

 tubers of rounded depressed areas, about 2 mm. in diameter, dark 

 brown in colour, with a somewhat lighter coloured, rather well- 

 marked margin, the central portion of each of these shallow pits 

 being usually somewhat raised. He obtained a strong growth of 

 a fungus by exposing cut surfaces of spot to a moist atmosphere. 

 The fungus was identified for him at Kew as Siricaria solani. It 

 is possible this species was present, but if so it was probably 

 secondary. No cultural or infection experiments were made. 

 His remarks were illustrated by photographs showing very 

 typical diseased tubers. 



Milburn and Bessey in their work " Fungoid Diseases of Farm 



Blotches 

 evidently 



and Garden Crops, 5 ' 1915, describe under the heading " 

 or pimples" (pp. 90-91), a spot on potato tubers < 

 identical with the present disease. They refer to Carruthers' 

 paper, and give Spicaria timed as the causal organism. They 

 remark that the spots, though visible at lifting time, are more 

 noticeable after storing, and point out that not only do they 

 render the tubers unsightly and thus reduce the market value, 

 but they may destroy the eyes. They further refer to a case of 

 " Evergood " producing a very irregular crop through the eyes 

 being killed. As far as can be seen from their illustrations, the 

 fungus observed was identical with that described in the present 

 paper. Dr. Milburn informs me that the development of the 

 spot during winter was particularly noticeable on the warp soils 

 of Lincolnshire. 



Giissow, in a brief note, describes Skin Spot os occuring in 

 Canada, on potatoes from Quebec (Phytopathology, 8 No. 9, 

 pp. 493, Sept. 1918). He illustrates his remarks with an 

 excellent photograph and states that it is identical with that which 

 he saw in England when working -with Carruthers (in 1904). 

 Although he admits the presence of fungal hyphae in the 

 diseased areas, he attributes the disease to bad ventilation during 

 storage, and considers that it occurs most frequently in those 

 cellars where the potatoes are covered with soil to guard against 

 the effects of frost. 



In the first Annual Report of the Plant Disease Survey, under- 



taken by the Food Production Department of the Board of 



• 





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