16 BULLETIN 64, U. S. DEPAETMENT OF AGKICULTUEE, 



It is the writer's opinion that under present conditions this is not 

 a quarantinable disease. It is ver}'- widely distributed in the United 

 States, as already shown. It would be difficult to establish the 

 boundaries of infected areas, and almost impossible to apply quaran- 

 tine restrictions without serious injury to commerce. Nor is it 

 certain that the aim desired would be accomplished in this way. 

 There are so many avenues for the sj)read of plant diseases that it 

 often seems as if onh^ ocean barriers were of avail. (Lounsbury, 

 1909, 1910.) 



OCCURRENCE OF AMERICAN FUSARIUM WILT IN EUROPE. 



The bulletin by Smith and Swingle had its influence on European 

 patholog}?-, inasmuch as the leaf -roll epidemic, which began in 1905, 

 was at first believed to be a Fusarium disease. The fact that none 

 of the European workers had seen the American disease and that no 

 American pathologist famihar with wilt had seen the leaf-roll in 

 Europe led to further confusion. 



The writer now beheves that there is no evidence that the American 

 wilt disease occurs in Europe. This statement is based on observa- 

 tions made in the course of a study trip through Germany, Austria, 

 and England in 1911.- No cases of typical Fusarium wilt were seen. 

 Furthermore, Dr. . Wollenweber, in the morphological studies later 

 mentioned, has been able to differentiate the Fusarium oxysporum of 

 Smith and Swingle from other potato Fusaria, and he finds this to be 

 distinct from any Em'opean form. Inasmuch as he studied critically 

 the Fusaria isolated from leaf-roU material while at Dahlem, Berlin, 

 this result is very significant and goes far to explain the difficulty 

 German workers have had in verifying the observations of Smith and 

 Swingle. Himmelbaur (1912) reports Fusarium to occur in much of 

 the leaf-roll material studied by him in Austria, but he has not 

 identified the species, and until this is done his results can not be 

 correlated with the results of American workers. 



VERTICILLIUM WILT. 



DESCRIPTION OF THE DISEASED PLANTS. 



The Verticillium wilt of potatoes is characterized by a wilting or 

 blighting of the foliage, resulting in the premature death of the hill. 

 The vascular bundles of the stem, the stolons, and usually of the 

 tubers, are filled with the mycelium of Verticillium alho-atrum. The 

 spores of this fungus often cover the dead stalks, so that they 

 become conspicuous from their gray color. 



As observed by the writer in this country and in England in 1911, 

 plants attacked by Verticillium wilt generally die quickly. There 

 may be yellowing of the foliage, but the drooping and wilting has 

 been pronounced in most of the cases observed. The Verticillium wilt 



