Jan. 24,1916 
Sweet-Potato Scurf 
789 
centers of infection, in view of the fact that conidiophores often 200^ in 
length stand erect or at an angle on the surface of the potato and drop 
their spores, starting new infections outside the point of original growth. 
The spots, however, so far as the writer has been able to determine, do not 
enlarge by the branching and creeping of the hyphae over the surface. 
Repeated inoculation experiments gave similar results. The checks 
remained free from the disease. 
DESCRIPTION OF THE FUNGUS 
The young vegetative growth of Monilochaetes infuscans is hyaline 
and septate. At the end of a few days, however, with the exception of 
the terminal cell of the conidiophore, the hyphae turn densely brown. 
On the host little or no branching of the vegetative growth takes place. 
Although Halsted figured a branching of the hyphae which was hyaline 
in color within the tissues of the host, the writer, after long and detailed 
examination of paraffine sections and sections prepared in other ways, 
has not been able to find a sure example. The sporophores, for such 
they appear to be, arise from the surface of the host and are attached to 
it by an enlarged end cell slightly buried in the cuticle (PI. LVIII, 
F, C, D). Occasionally a second (PI. LVIII, I) or third (PI. LVIII, J) 
enlargement or bulblike growth is found deeper in the host or parallel 
with the surface (PI. LVIII, G), From some of these secondary enlarge¬ 
ments a conidiophore may be developed (PI. LVIII, F, H). Plate LVIII, 
F, C, shows conidiophores bearing conidia produced on the host. The 
brown septate conidiophores vary in length from 40 to 175/i and bear at 
the end a single-celled spore, which on the host is slightly brown or 
hyaline. The conidia are 12 to 20/z in length by 4 to 7 m in thickness. 
This fungus, as might be expected, behaves differently when grown 
artificially. Growth has been carefully observed on a few of the com¬ 
mon media—namely, Irish-potato agar, beef agar, rice agar, oatmeal 
agar, string-bean agar, Irish-potato cylinders, sw'eet-potato stems, and 
stems of Melilotus alba . At the end of 24 days a very slight growth 
appeared on string-bean agar, rice agar, and oatmeal agar at a tempera¬ 
ture varying from 6° to 7 0 C. Conidia were very sparingly produced. 
# At room temperature (23 0 to 26°) growth was visible on all media in 4 
days, except on rice agar and the stems of sweet potatoes and Melilotus 
alba . In 13 days a small growth appeared on rice agar, but on stems of 
sweet potatoes and sweet clover no growth was detected at the end of 
4 weeks. There is very little difference in the gross appearance of the 
growth on any of the media used. Enlargement from a single center is 
very slow, attaining a diameter of about 2 to 5 mm. in 14 days. The 
fungus piles up in an almost black feltlike mass 2 to 3 mm. in height, 
with an entire margin. It penetrates the medium but little. The vege¬ 
tative hyphae in mass are almost charcoal-black, although in gross appear¬ 
ance there is some variation on different culture media. On Irish- 
