oct. 3o, 19x6 Spongospora subterranea and Phoma tuberosa 
221 
Twelve plants with strong root systems and from 8 to 10 inches high 
were washed and transplanted from clean to infected land in the field on 
August 5, the day on which root infection was first discovered, and for 
three or four days they were well watered and shaded. On August 19 
three of the plants were taken up and the roots examined, but only one 
gall was found. However, when the nine others were dug, on September 
3, and the roots examined, from 3 to 11 galls each were found on 6 plants, 
which suggests that from 14 to 34 days must elapse after the plant reaches 
a certain stage of development before infection with Spongospora sub - 
terranea takes place. 
A similar experiment was begun on September 7, plants of approxi¬ 
mately the same age as those used on August 5 being transplanted from 
healthy to diseased soil. The plants were dug on October 1 and the root 
systems and tubers carefully examined, but no infection was found. 
The small amount of infection in the case of the first experiment and 
absence of infection in the second is explained by the fact that very few 
infections took place on any of the plants on the plots after August 15, 
as previously noted. 
With a view to determine whether the plant must be a certain age 
before infection can take place, 200 seed pieces were planted on July 26 
in infected soil in the field. On August 20, when the plants were 3 inches 
high and had extensive root systems, 100 hills were dug and examined, 
but no infection was found, although in an adjoining row planted on May 
26 the roots were generally infected, infection having occurred between 
August 1 and 15. On September 24 the remaining hundred hills were 
dug and examined, but no infection was found, although doubtless the 
plants had some roots by August 15, which tends to indicate that the 
host tissue had not reached the susceptible stage. 
Very little is known about the factors that favor infection. Moisture, 
however, is doubtless an important limiting factor. Lime increases the 
amount of powdery-scab on the roots and tubers. Root galls were 
especially large and abundant on the plots that received lime at the rate 
of 3,000 pounds per acre. That injuries also increase the tendency to 
infection was indicated by the finding of numerous galls on lesions 
caused by fungi other than Spongospora subterranea. In one case four 
galls were found on an injured portion of a plant that had been partially 
broken off and had recovered, the indications being that infection had 
taken place after the injury. 
NEW HOSTS OF SPONGOSPORA SUBTERRANEA 
As soon as it was found that Spongospora subterranea infects the root 
system of the potato plant, investigations were undertaken to determine 
whether it infects the roots of other solanaceous plants. Fifty-three 
species of solanaceous hosts were planted at Caribou on June 2, 1915, in 
powdery-scab-infected soil in adjoining beds about 3 feet square, potatoes 
