28 BULLETIN 64, U. S. DEPARTMENT OF AGEICULTUKE. 



from whom so much, has already been drawn, the ones deserving of 

 special mention are those of Dr. Schander, in the Kaiser WUhelms 

 Institut fiir Landwirtschaft in Bromberg and of Dr. Spieckermann 

 in Muenster. So many others have ^vritten on this subject that it is 

 possible only to refer to the extensive bibhographies of Appel and 

 Schlumberger, 1911, of Kock and Kornauth, 1911 and 1912 

 (Mitteilungen des Komitees zum Studium der BlattroUkrankheit, 

 Nos. 2 and 5), and of Himmelbaur, 1912. 



GEOGRAPHIC DISTRIBUTION OF LEAF-ROLL. 



Much is lacking in the knowledge of the exact distribution of the 

 leaf-roll diseases, but it begins to appear that it is now, or soon will 

 be, a factor in potato culture wherever this crop is grown. Its 

 occurrence is certain in Germany, Austria-Hungary, Switzerland, 

 the Netherlands, Denmark, and Sweden, as well as in the United 

 States. It is probably in Norway, Russia, Bulgaria, and Roumania. 

 That it has not been reported in France, Belgium, and England may 

 be because of lack of sufficient observation. The somewhat Hmited 

 observations of the writer in these countries in 1911 failed to disclose 

 any true leaf-roll. The disease reported under that name from 

 Ireland is the VerticiUium wilt. 



In Germany the leaf-roll has been most widespread and injurious 

 in the west, e. g., in Westphalia and the Rhine provinces, though 

 since its first outbreak in 1905 the introduction of healthy seed stock 

 from other districts is reported to have restricted its spread. Leaf- 

 roll has been observed in nearly aU parts of Germany, but in most 

 cases only scattered fields suffered. 



In Austria, also, the disease seems to be present in nearly all dis- 

 tricts, including Hungary, though not always to a destructive degree. 



OCCURRENCE OF LEAF-ROLL IN THE UNITED STATES. 



Two developments of leaf-roll in this country have been studied 

 by the writer. One was in a collection of seedlings grown by Prof. 

 Wilfiam Stuart, of the Bureau of Plant Industry, and the other was 

 a destructive outbreak in eastern Colorado and western Nebraska 

 during 1911 and 1912. The leaf-roU in the seedhng collection, while 

 not of direct economic importance, afforded an opportunity to 

 <liagnose the trouble and differentiate it from others and also sug- 

 gested a probable solution of the problem of control. 



The western outbreak was, on the other hand, the cause of immense 

 losses and brought the leaf-roll problem, for the first time, to the 

 forefront in this country. That it will continue to be an important 

 economic factor in American potato production is indicated by its 

 discovery in two new locaHtics in 1913. The writer found a field of 

 Irish Cobbler near Onlcy, Va., with well-marked leaf-roll character- 

 ized by rolled leaves Avith a reddish tinge and stunted growth. The 



