8 BULLETIN 64, V. S. DEPAETMENT OF AGEICULTUEE. 



cultm-es on potato and sixteen on agar were fnade, and in all but two cases on the potato 

 and in every case on the agar the fungus appeared after a day or two as a white myce- 

 lium, sparse at first, gi-owing directly out from the blackened bundle, and spreading 

 into the media. Forty-two cultures on potato and foiu- on agar were also made from 

 older parts of the discolored ring nearer the basal end, and of these all but one on the 

 potato and all on the agar produced a growth of the fungus. 



The relation of these tuber infections to stem-end dry-rot will be 

 described more fully in another publication. A dry-rot of the tuber 

 was considered by Smith and Swmgle to be caused by the same 

 Fusarium which produces the wilt of the foliage, but the recent 

 studies of Wollenweber (1913) have shown that Fusarium oxysporum 

 is a vascular parasite causing wilt and wintering over in the tubers, 

 where it produces a stem-end vascular discoloration, but no decay. 

 Tuber dry-rot is caused by one or another of the following fungi, 

 which follow F. oxysporum or infect through wounds, viz : F. coeru- 

 leum (Lib.), F. triothedoides Wr., F. discolor var. sulpTiureum Schlecht, 

 F. ventricosum App. and Wr.; and probably sometimes also the less 

 parasitic F. gibbosum App. and Wr., and F. suhulatum App. and Wr. 



SOIL RELATIONS OF FUSARIUM WILT. 



The Fusarium wilts of cotton, watermelon, and cowpea occur 

 principally on sandy- and sandy-loam soils and are practically re- 

 stricted to them. That siich is the case with the potato wilt is by no 

 means clear, though there is evidence indicating that light soils are 

 more liable to infection. The California tule lands, where wUt is 

 perhaps more prevalent, are reclaimed and artificially drained peat 

 islands, with a very light and friable soil, composed almost wholly of 

 organic matter. In Oregon, Utah, and Colorado, however, wUt 

 occurs on heavier soils, varying from sandy loam to clay loam. 

 Potatoes thrive best in light, deep, and well-drained fertile soils, and 

 it appears that the wilt is more likely to develop in any such good 

 potato soils than under conditions unfavorable to the crop. 



THE PARASITISM OF FUSARIUM OXYSPORUM. 



That the fungus Fusarium oxysporum is parasitic upon the potato 

 plant has now been proved with reasonable certainty. Smith and 

 Swingle established the fact of its constant occurrence in the vascular 

 tissues of plants suffering from the wUt disease, by means of very 

 numerous pure cultures. No inoculation experiments were under- 

 taken by them, but successful infections have since been reported 

 by Manns (1911) from the Ohio Agricultural Experiment Station, 

 and cultures of the Ohio strain have been studied by Dr. H. W. 

 Wollenweber in comparison with a large number of others isolated 

 from collections made by the writer from diiferent parts of the 

 United States or sent in by correspondents, and nearly all have 

 proved to be the species we continue to call F. oxysporum Schlecht. 



