Oct. 30,1916 Spongospora subterranea and Phoma tuberosa 
249 
never been able to produce larger lesions, which is significant, as in nature 
larger lesions are rarely found unless other wound parasites have entered. 
A tuber from one series of inoculations in which lesions are only 6 mm. 
in diameter are shown in Plate 13, figure E, and a series which produced 
much larger lesions in Plate 13, figure C, and for comparison tubers 
naturally infected are shown in Plate 13, figures A and B, and Plate 11, 
figure A. A tuber injured but not inoculated is also shown in Plate 13, 
figure D. 
Table XV gives the results of a series of inoculations made during the 
course of the work. 
Tabi^E XV .—Results of inoculating potato tubers with Phoma sp. in 1915 
Date of inoculation. 
Number 
of inocu¬ 
lations. 
Percent¬ 
age of in¬ 
fection. 
Condition of 
control. 
March 26. 
18 
88 
Healthy. 
Do. 
April 3.. 
18 
IOO 
April 13... 
6 
66 
Do. 
April 23.. 
24 
6 
9 ° 
66% 
66% 
5 o 
90 
Do. 
May 1 . 
Do. 
May 10. 
Q 
Do. 
May 15 . 
7 
8 
Do. 
May 27 . 
10 
Do. 
In the series of inoculations made on May 1 new potatoes were used. 
The fungus was able to produce very slight infection on these new pota¬ 
toes, but the lesion never exceeded 3 mm. in diameter. The tubers inocu¬ 
lated May 10 showed only a slight infection. These tubers were held in 
the moist chamber until May 25, when they were examined. The in¬ 
fected area at this time measured 3 mm. in diameter, and in one inocula¬ 
tion scattered pycnidia could be seen with the naked eye and were as 
abundant near the edge of the spot as in the center. Reisolations were 
made on poured plates of potato agar from the inoculations made on 
March 26, April 3, and May 27, and in every case a pure culture of a 
fungus, macroscopically and microscopically identical with the culture 
used for inoculation, was obtained. Plate 14, fig. B, shows a section of 
one of the inoculated tubers. Most of the mycelium of Phoma tuberosa 
is beneath the epidermal cells. This mat later gives rise to the pycnidia, 
which grow towards the surface of the tuber. 
CULTURAL CHARACTERISTICS 
Tests made with the fungus on a number of media showed that it 
grows well on sterilized sweet-clover (Melilotus alba) stems, potato hard 
agar, potato cylinders, corn meal, and Beyerinck’s agar. The luxuri¬ 
ance of its growth on all of these leaves no doubt that it is able to grow 
