i9o8.] 



"Corky Scab" of Potatoes. 



599 



According to Professor Johnson, practically all the potatoes 

 in the west of Ireland are scabbed, and the planting of scabbed 

 " sets " is unavoidable. 



It may be stated that by soaking diseased potatoes for 

 two hours in a solution consisting of half-a-pint of formalin 

 in 15 gallons of water, the parasite located in the superficial 

 cells of the potato is killed. It is very doubtful, however, 

 whether a plasmodium lying somewhat deep in the tissue of 

 the potato would be affected by this treatment. Under any 

 circumstances it is a very risky and unwise practice to plant 

 diseased " sets." 



It has been definitely proved that the application of lime 

 prevents the disease known as " club-root " or " finger-annd 

 toe " in turnips and other cruciferous plants, and as the 

 organism causing " corky scab " is very closely allied to the 

 " club-root " parasite, it seems possible that the check for the 

 one disease may prove to be a check for the other. 



Bibliography. 



Berkeley, M. J. , Journ. Hort. Soc, 1, p. 9, pi. 4, figs. 30-31 (1846). 

 Berkeley, M. J., Ann. Mag. Nat. Hist., June, 1850, p. 26. 

 Fischer de Waldheim, A., Apercu sy stematique des Ustilaginees (1877). 

 Brunchorst, A., Bergens Museums Aarsberetn., 1886, p. 219. 

 Johnson, T., Economic Proc. Roy. Dublin Soc, I, p. 253 (1908). 



Description of the Figures. 



Fig. 1. — Typical example of scab in early stage of development. 

 ,, 2. — Section of scabbed tuber in early stage of development. 

 ,, 3. —Section through a "scab" showing a mass of spore-balls, also the 



formation of wound-cork below the seat of injury. 

 ,, 4. — The earliest observed condition of4he parasite, under the form of motile 



bodies, in a cell of the host. 

 ,, 5. — A later stage of the parasite, where the motile bodies shown in fig. 3 



have coalesced to form a plasmodium. 

 ,, 6. — The stage following the condition shown in fig. 5'; the protoplasm, owing 



to vacuolation, has assumed the appearance of an irregular hollow 



sphere with several large, irregular cavities in the wall. 

 7- — The stage following the appearance shown in fig. 6; the wall of 



the sphere has become resolved into a series of closely packed cells, 



one layer in thickness, forming a spore-ball. 

 ,, 8-9. — Two mature spore-balls that have become liberated, owing to disintegra- 

 ' tion of the cell-walls of the host. 



10. — A few cells from a spore-ball. Three of the cells still contain their 



contents. Originally one nucleus is present in each cell. The con- 

 tents have escaped from two of the cells. 



11. — Escaped contents of cells, which are at first motile, and soon divide by 



fission. 



j> 12. — Nuclei in a small portion of plasmodium. 

 (Figs. 1 & 2. — Natural size ; the remainder highly magnified.) 



