SCABBINESS OF TUBERS. 15 



from seal)." Since this is often on rich and heavy land, such as would 

 develop scab under like treatment in America, the European experi- 

 ence is diihcult to understand. Does not our type of disease exist 

 there, or is it less virulent because of some difference in the climatic 

 and soil conditions? The writer is not prepared to answer with full 

 contidence, but his judgment favors the second suggestion. 



Europeans, both pathologists and practical men, recognize more 

 than one form of disease under the name of scab (the German 

 " schorf ," Dutch " schurft," French ''la gale "). Frank's subdivisions* 

 of "schorf into four kinds — flach, tief, buckel, and buckel-tief 

 schorf — were familiar to the continental pathologists interviewed, but 

 the general opinion is that these are simply forms of one common dis- 

 ease, the variations being attributable to the season of attack or to 

 varietal or vegetative conditions of the potato. Frank's specimens of 

 " tief -schorf " were seen in the museum of the board of health at Berlin 

 and have the appearance of the common American scab. 



As to the cause, opinions differ.'" The German pathologists who have 

 given most attention to this disease consider the commonest German 

 form to be due to a fungus similar to Thaxter's Oospora scabies^ but 

 perhaps not identical with it. In Holland doubt was expressed as to 

 the common Dutch form of potato scab being a fungous disease at all, 

 while in Belgium and France it is considered a parasitic disease, but 

 due to bacteria {Micrococcus pellic id us Roze) rather than to fungi.'' In 

 England Oospora scabies is held responsible for only the minor part of 

 the trouble, Sorosporitmi scabies Fisch. being the commoner parasite. 



VARIETAL RESISTANCE TO SCAB. 



As already stated, none of these scab diseases has proved of suffi- 

 cient economic importance to attract much attention from practical 

 potato growers in P^urope. Probabl}^ most of the diseases would yield 

 to the seed-disinfection treatment practiced for potato scab in America, 

 yet this is nowhere used by European growers, so far as learned. 

 The only valuable data as to the relative susceptibility of varieties to 

 scab are those furnished by the reports of Professor Eckenbrecher,^ 

 whose results point to certain newer varieties as being comparatively 

 free from scab, while others are quite susceptible. Age of the variety, 



«See Sutton, A. W., Potatoes, Jour. Roy. Soc, XIX, pp. 387-430 (1896). 



^Kampfbuch, p. 170. 



'These conclusions are the result of conferences with a number of men and reference 

 to the publications of others. Among those who have given this disease careful con- 

 sideration in their respective countries and whose opinions were learned are Professors 

 F. Kriiger, Berlin; Ritzema-Bos, Amsterdam; Marchal, Gembloux; Roze and Dela- 

 croix, Paris; Massee and Cooke, England. 



''Roze, E., Histoire de la pomme de terre, Paris, 1898, p. 275. 



«C. von Eckenbrecher, Berichte Deutsch.-Kart.-Kult.-Stat., 1903 and earlier. 



