8 BULLETIN 64, U. S. DEPARTMENT OF AGRICULTURE. 
cultures on potato and sixteen on agar were made, 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, growing directly out from the blackened bundle, and spreading 
into the media. Forty-two cultures on potato and four 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 Swingle 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. triothecioides Wr., F. discolor var. sulphureum Schlecht, 
F. ventricosum App. and Wr.; and probably sometimes also the less 
parasitic F. gibbosum App. and Wr., and F. subulatum 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 such 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 wilt 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, wilt 
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 wilt 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 different 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. 
