oct. 30,1916 Spongospora subterranea and Phoma tuberosa 
243 
the market, but it may be followed by a rot which will render the tuber 
worthless for either table or seed purposes. 
Naturally the question arose as to whether tubers infected with Spon¬ 
gospora subterranea harvested while immature will rot more than such 
tubers harvested when mature; and in order to get light on this phase of 
the subject, experiments were carried on with the crop of 1914. About 
two weeks before the harvest season, or on September 9, 91 tubers were 
dug from the experimental plots and examined. Out of the total num¬ 
ber, 67 showed various stages of infection, ranging from a few small, 
immature pustules to a generous sprinkling with sori, while 24 were free 
from the disease. After this the diseased tubers were placed in one sack 
and the healthy tubers in another, and both sacks were placed in a potato- 
storage cellar, such as is commonly used in northern Maine. On June 15, 
1915, both sacks were examined, and it was found that of the 61 tubers 
in the sack containing the infected potatoes 31 were two-thirds or wholly 
rotten, 4 had rotten spots from 2 to 4 cm. in diameter, and 32 had rotten 
spots from 1 to 2 cm. in diameter. With one exception, which was per¬ 
fectly sound, the sori apparently having corked over perfectly and pre¬ 
vented the entrance of fungi, all the tubers generally infected with 
sori of S. subterranea were rotten. The 32 tubers with small dryrot spots 
consisted of those which showed few small sori of 5. subterranea . Of the 
24 tubers in the sack containing the healthy potatoes, 3 were two-thirds 
or wholly rotten, 1 had a rotten spot 2 cm. in diameter, and 20 were 
sound, except in the case of 2 which were infected with common scab. 
In another case 1 bushel of powdery-scab-infected tubers was col¬ 
lected from a field at the beginning of harvest, or on September 24. At 
this time the tubers were not fully mature, and the sori in most cases 
had not ruptured the epidermis; but the badly infected specimens 
showed brownish purple areas. These potatoes, together with others, 
were placed in storage. When examined for the development of the 
rot, on June 10, 1915, 63.9 per cent of the tubers were found to be 
decayed two-thirds or more, and the collection was in such a condition 
that it could scarcely be handled. In every case the sound tubers were 
those which showed but little powdery-scab. 
From these results it is evident that powdery-scab dryrot becomes 
much worse on potatoes harvested early than on those harvested after 
the tubers are fully mature. 
In another case 620 tubers, the progeny of no hills in a field infected 
with powdery-scab, were harvested on November 7, 1914, the potatoes 
being dug by hand. Each tuber was carefully examined, and it was 
found that 63 per cent of the lot by weight was infected and that the 
progeny of only two hills was free from the powdery-scab. The healthy 
tubers, numbering 295, and the tubers infected with S. subterranea , 
numbering 325, were put in separate sacks and placed in storage on 
November 9, 1914. When taken out and examined, on June 14, 1915, 
55859°—16-3 
