788 
Journal of Agricultural Research 
Vol. V, No. 17 
Scurf is more prevalent in heavy, black soils and in soils that have 
been heavily manured or contain a larger amount of organic matter than 
in light, sandy soils. 
The loss to the crop caused by the scurf is perhaps small in comparison 
with that caused by some of the more virulent diseases. Nevertheless, 
the actual financial loss throughout the country that can be attributed 
to this disease alone amounts to considerable. Scurfy potatoes do not 
command as high a price in the markets as clean ones, though if otherwise 
sound they are just as good for consumption. The fungus under favorable 
conditions, such as a relatively high humidity and temperature, continues 
to develop under storage conditions to a limited degree. It weakens the 
host, so that during periods when the storage house is rather dry the 
potato loses moisture and becomes shriveled and dried, rendering it unfit 
for sale and at the same time less resistant to the attacks of other para¬ 
sites. Taubenhaus 1 claims that the fungus on the potato is easily killed 
by immersing for io minutes in a solution of mercuric chlorid (i: 1,000). 
ISOLATION OF THE FUNGUS 
Some difficulty was experienced at first in isolating the fungus, since it 
proved to be a very slow grower and developed but little or not at all on 
some kinds of media. After some experimentation with different media 
it was found to make a slow growth in Irish-potato, string-bean, and 
oatmeal agar. By thoroughly washing the potato and disinfecting for 
about one minute in a solution of mercuric chlorid (i: i ,000) and planting 
bits of the tissue in plates of oatmeal agar by means of sterile instruments 
a pure culture could generally be secured. In a week or 10 days transfers 
were made to media in test tubes, usually cooked rice in water or sterile, 
moistened com meal. At the end of three or four weeks on these media 
a matted growth of dark-brown hyphae developed. Hyaline spores are 
produced in abundance on long, stout conidiophores in tubes of cooked 
rice. 
INOCULATION EXPERIMENTS 
Inoculation experiments were begun on October 13,1914, and performed 
as follows: Sound potatoes were thoroughly washed in water and placed 
in moist chambers with moistened filter paper in the bottom. They were 
then sprayed with a suspension of spores and bits of broken hyphae of the 
scurf fungus in sterile water and exposed to laboratory room conditions. 
Water was added from time to time, as necessity required, to maintain 
the humidity of the moist chamber. At the end of two weeks small 
centers of infection appeared indiscriminately over the surface of the 
potatoes. These centers gradually enlarged, either by the merging of two 
or more spots or by the enlargement from a single center. There is un¬ 
doubtedly considerable enlarging of the spots in moist chambers from 
1 Taubenhaus, J. J. Soil stain and pox, two little known diseases of the sweet potato. (Abstract.) In 
Phytopathology, v. 4, no. 6, p. 405. 1914- 
