POTATO WILT, LEAF-EOLL, AND RELATED DISEASES. 17 



seen in Germany appears to be slower in causing the death of the 

 plants, a difference possibly attributable to temperature and rainfall 

 factors. The browning of the vessels is also marked, often extend- 

 ing to the tips of the stems and into the leaf petioles. There has " 

 been also a pronounced discoloration of the stem end of the tubers 

 in all the cases observed. 



Verticillium wilt is often not strikingly different from Fusarium 

 wilt in outward appearance, though it may induce a more rapid 

 wilting. The presence of the mycelium and vascular browning in 

 the upper portions of the plants is indicative of Verticillium, as Fusa- 

 rium does not usually extend into the tips of the stalks. The profuse 

 production of conidia on the stalks, often before they are entirely 

 dead, is still more characteristic. The stain in the stem end of the 

 tubers is blacker, and in cross sections under the microscope the 

 vascular bundles are found to contain hyaline mycelium smaller 

 than that of Fusarium oxysporum. The final proof of the identity 

 of the disease comes, of course, when cultures made from the internal 

 mycelium yield Verticillium albo-atrum. 



So far as observations go, Verticillium wilt occurs in scattered hills 

 here and there over the fields. The destruction of entire crops, such 

 as is frequently caused by Fusarium oxysporum, has not been seen. 



GEOGRAPHIC DISTRIBUTION. 



VerticUlium wilt has been collected by the writer since 1909 from 

 the State of Washington (La Conner) to Maine, but only in the more 

 northern States. It has been seen in Vermont (Franklin County) 

 and western New York, but in neither case in abundance. The vari- 

 eties most attacked were Factor and Up-to-date, from seed originally 

 from England. It is believed that the Verticillium infection came 

 with the seed potatoes. The same fields planted to other varieties 

 in 1913 were free from wilt on August 1 and 4. 



The writer collected the same disease in Olmskirk, England, Sep- 

 tember 11, 1911, and the fungus was isolated from a tuber (said to 

 have come from Scotland) found in Reading, England. Its occur- 

 rence in Ireland is vouched for by Pethybridge (1911). It appears 

 to be common in Germany, judging by the frequency with which it 

 is mentioned in connection with leaf -roll investigations there. In- 

 deed, it was described by Reinke and Berthold as long ago as 1879, 

 and the writer saw it at Munster in Westphalia in October, 1911, 

 where it was studied by Spieckermann (1911), who pointed out the 

 difference between this wilt and the fungus-free leaf-roll. Verti- 

 cillium wilt is apparently a northern disease as compared with 

 Fusarium, though the ranges of the two undoubtedly overlap. 



Pethybridge (1911) in Ireland describes this disease under the 

 name '' leaf -roll, " distinguishmg it from "curl," the latter being the 



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