26 o 
Journal of Agricultural Research 
Vol. I, No. 3 
Pycnidia were abundant on eight of the diseased plants when lifted on April 22. The 
one remaining diseased plant was lifted on April 26, and pycnidia were then present. 
The experiment was terminated April 26, 1913. 
Experiment No. 20.—On March 13 six young sweet-potato plants were inoculated 
by inserting spores and hyphae into the lower part of the stem with organism No. no 1 
(culture No. 3 of Mar. 5). Five plants were left as checks. 
Results.—On April 18 two plants, on April 22 two, and on April 23 one, or a total 
of five plants, were infected. The diseased plants were lifted on April 26, and pyc¬ 
nidia were present on all. None of the check plants were diseased. The experiment 
was terminated April 26, 1913. 
Inoculations in the Laboratory 
Experiment No. 21.—On November 18 eight mature sweet potatoes (not plants) 
were inoculated by inserting pycnospores and hyphae of organism No. 101 (culture 
No. 8 of Oct. 31) into the end of the potatoes. They were placed in cloth bags and 
stored in the laboratory. Four potatoes pricked with a sterile needle were used as 
checks. 
Results.—No infection. The experiment was terminated January 31, 1913. 
Experiment No. 22.—On April 4, 1913, six sound sweet potatoes were prepared 
for inoculation by cutting away the ends of each so as to leave nothing but healthy 
tissue. They were then thoroughly washed and disinfected by treating with mer¬ 
curic chlorid (1:1,000) for five minutes. They were afterwards rinsed in sterile 
water and placed in a moist chamber on filter paper disinfected with corrosive sub¬ 
limate. Three of the potatoes were inoculated at the end and three at the side by 
inserting spores and hyphae of organism No. 108 (culture No. 1 of Mar. 8). Four 
other potatoes pricked with a sterile needle were used as checks. 
Results.—On April 15 no signs of decay had started at the point of inoculation. 
The filter paper appeared a little dry, and sterile water was added. After April 15 
the rot developed and progressed rapidly in all the potatoes from the point of inocula¬ 
tion until by May 1 one potato was completely decayed and the others about one-third. 
Plate XXVIII, figure A, shows a sweet potato inoculated at the end and figure C, 
one inoculated at the side. Figures B and D are sections of figures A and C, respec¬ 
tively, showing the extent of the rot. The potatoes' inoculated at the side decayed 
more rapidly than those inoculated at the end. Mature pycnidia and spores were 
formed on the surface on May 1. The organism was recovered from the pycnidia and 
from the diseased brown tissue of two potatoes. 
The organism causes a chocolate-brown to almost black discoloration of the tissue, 
but leaves it rather firm, even in the later stages. This is not a distinctive character¬ 
istic, since there are a number of rots of the sweet potato, nearly all of which produce 
some shade of brown in the tissue and are in general so similar that it is practically 
impossible to separate them by their macroscopic appearances. All of the check 
potatoes remained sound. 
1 This organism was obtained from plants of Ipomoea coccinea which were inoculated with organism No. 
ioi. 
