Oct. 30,1916 Spongospom subterranea and Phoma tuberosa 
247 
ISOLATION STUDIES 
During the past three years a large number of isolations were made 
from the dryrot lesions, and a considerable number of parasitic and 
saprophytic organisms, including species of Coniothyrium, Ramularia, 
Periola, Fusarium, Phoma, Rhizoctonia, Vermicularia, Papulospora, and 
Bacteria, were studied as regards their relation to dryrot. 
A type of spot, which at first had brownish to gray lesions and later 
became hard and dark (Pi. 13, fig. A, B), was found to be very common, 
not only in connection with Spongospora subterranea but also on tubers 
free from this disease, the senior writer (7) having found it in Maine 
before the presence of 5. subterranea had been reported. 
When not associated with any of the fungi above mentioned, the 
rot caused by the species of Phoma under consideration in section is 
slate-colored, dry, and powdery; but when other fungi are associated the 
tissues of the tuber show cavities or chambers and the color is character¬ 
istic of the mycelium or spores of the fungus present—that is, white and 
blue in the case of Fusarium coeruleum , light green or sulphur-colored in 
the case of F. discolor , var. sulphureum , and dark brown when Papulo¬ 
spora coprophila is the secondary saprophyte. The following studies 
indicate the distinctive characteristics of the rot caused by the species of 
Phoma under consideration. 
Twenty tubers showing typical symptoms were selected for these 
studies. These were washed and immersed in mercuric chlorid (1:1,000) 
for 10 minutes, after which the surface tissue was peeled off and plant¬ 
ings made from the newly exposed tissue. In the majority of cases the 
plantings gave a pure culture of a species of Phoma. The isolations 
were made from button-shaped spots associated with and apart from 
Spongospora subterranea , and similar results were obtained in each case. 
In order to get more accurate data regarding the association of the 
fungus with the lesion, a more detailed study was made. Twenty tubers 
having typical lesions were selected on May 17, 1915, an effort being 
made to secure tubers in which no other wound fungi had entered. The 
lesions, which varied from 6 to 25 mm. in diameter, were firm to the 
touch, dark gray, and had the appearance of typical button-shaped spots. 
The isolation from each tuber was made on a separate plate, and 4 plant¬ 
ings were made on each plate, or a total of 80. These were examined on 
May 20, and the number and kind of colonies found on each are shown 
in Table XIV. 
As shown by Table XIV, the 80 plantings produced 6 bacterial and 46 
fungus colonies. Microscopic examination showed that the latter in¬ 
cluded at least three different groups of fungi: One containing 2 colonies, 
one 38 colonies, and one 6 colonies. 
In order to check up the identity of these colonies, 2 transfers were 
made from each of the 46 colonies, to test tubes of potato hard agar and 
