ON POTATO " LEAF BLOTCH " AND " LEAF CURL." 



623 



Leaves rolled, curled 

 ' - or partly folded 



Massee states that Blackleg is at present rare in Britain, but that 

 it is very destructive in its effects. 



A rolHng or curling of "the leaf, indistinguishable from that associated 

 with Blackleg in the Cleadon district, is frequently exhibited by plants 

 possessing no other visible symptoms of disease. For example, in 

 1910 I observed a number of young plants among those in my experi- 

 mental plots at Newcastle-upon-Tyne, *with leaves badly rolled or curled 

 (fig. 182) and sometimes wrinkled. Several plants were dug up, and in 

 most cases the subterranean stem had been cut by the hoe or presented 

 an unhealthy appearance. There were, however, no cases of Black- 

 leg. In other examples, there seemed no injury of any kind sufficient 

 to account for the condition of the foliage. 



The phenomena of the rolling or curling of the leaves of the potato 

 plant may occur, therefore, under the following circumstances : — 



( associated with no visible symptom of 

 disease. 



with accidental injuries to the 

 haulm. 



-{ ,, with a brownish discoloration 



of the subterranean stem, 

 with Blackleg. 



with a spotted or blotched con- 

 dition of the leaf. 



P. de Galuwe''' (1908), in Holland, and Eemy and Schneiderf 

 (1909), in Germany, give accounts of the prevalence of Leaf curl " 

 in their respective countries, where it appears to have become destruc- 

 tive to crops. If the state of affairs on the Continent be as bad as it 

 appears from published accounts, and if forms of disease which come 

 under the category of " Leaf curl " and " Leaf blotch " be imported 

 from the Continent, there is every reason to suppose that, sooner or 

 later, ** Leaf curl " and *' Leaf blotch," will be prevalent and destruc- 

 tive in Great Britain also. 



I desire to acknowledge my indebtedness to the Eoyal Society for 

 a Governm^ent grant in aid of the investigation of the more obscure 

 diseases of potato. 



* P. de Caluwe. Handel. Vlaamsch. Natuur en Geneesh. Cong. 12 (1908), 

 No. 2, pp. 195-200. 



t Eemy and Schneider. Fuhling's Londw Ztg., 58 (1909), No. 6, pp. 201-19. 



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