14 DISEASE EESISTANCE OF POTATOES. 



and termed eaHy-blioht in America. It is known, therefore, that it 

 occurs in Europe, but it can not be as common and destructive as it is 

 here, for no trace of it could be found in an}- of the fields visited. 

 Much was seen, however, of a leaf-spot disease which bears a super- 

 ficial resemblance to it. This was shown us first by Dr. Otto Appel in 

 the experimental fields of the board of health at Dahlem, near Berlin. 

 Later it was seen elsewhere in Germany and in Eno-land. Apparently' 

 there has lieen a confusion of this Avith our American early-blight," 

 but both Doctor Appel and Professor Sorauer stated that there was no 

 fungus present in this leaf-spot disease, and the writer's examinations 

 confirmed this. The cause of this trouble has not as yet been clearly 

 established, but since Appel and Sorauer both have it under observa- 

 tion, further advice may be expected upon it in the near future. 

 Opportunit}' was presented to compare the relative development of 

 this trouble on difi'erent varieties in the trial grounds of the University 

 Farm, Cambridge, England, in the latter part of the summer. There 

 was a considerable difference in the amount of spotting of the various 

 varieties, but none was altogether free from it. 



SCABBINESS OF TUBERS. 



POTATO SCAB. 



Scab-like diseases, i. e., those characterized by surface erosions of 

 the tubers, are frequent in Europe and apparently more varied -in 

 nature than is recognized to be the case in America. Yet nowhere 

 does injury to the crop from such diseases approach that which is 

 common in this country. This is in some ways surprising and unex- 

 plained. A disease closely resembling in appearance the common 

 American type of scab was frequentl}^ seen, but growers everywhere 

 in Germany, France, and Great Britain testified that it is not common 

 or destructive enough to be of much practical importance. Scientific 

 men are not agreed either as to the cause of the disease or as to the pos- 

 sibility of benefit from seed disinfection. But few recommended this 

 treatment, and no practical potato grower was met who practiced it. 

 The most puzzling thing, in the light of American experience, is that 

 potatoes are grown year after year continuously or in the shortest of 

 rotations on the same soil without increase of scabbiness. In each of 

 these countries potatoes are often grown on the same soil for ten or 

 twenty or even forty successive years with practically no trouble 



«See Frank, Kampfbuch, p. 220. Apparently the disease mentioned above is the 

 same as Frank's " Pockenfleckigkeit. " Frank was altogether mistaken in consider- 

 ing it the same as the American "early-blight," as Sorauer subsequently showed. 

 See also Bahna, J. J., Blattbraune der Kart. ; Zeitsch. f. Land. u. Fortwirtsch., 2: 113 

 (March, 1904). Prof. C. von Tiibeuf comments upon this article and reviews the 

 literature in the June, 1904, number of the same journal. 



