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Journal of Agricultural Research 
Vol. VII, No. s 
plant. The histology of the galls on all the hosts is very similar and has 
many points in common with Plasmodiophora brassiceae on cabbage. 
(7) The absence of the canker stage of S. subterranea in the United 
States may be due to the short growing period afforded the potato crop 
in infected districts. 
(8) Flea-beetle injury, intumescence associated with the lenticels, and 
certain forms of common scab on the tuber are often mistaken for stages 
of S. subterranea . 
(9) Among the saprophytic fungi found associated with the sori of 
S. subterranea is a species of Papulospora. The “bulbils” of the latter 
are strikingly similar to the spore balls of the former fungus, and this 
similarity may account for the confusion in earlier writings as to its 
identity on the potato tuber. 
(10) A study of early harvesting, seed treatment, varietal response, 
and soil treatment as control measures for the disease was made. This 
suggests that (a) early harvesting may be beneficial certain seasons in 
Maine, but can not be relied on every year; (b) seed treatment with 
certain chemicals will reduce the disease, this being especially true of 
mercuric chlorid and formaldehyde, the hot solutions for short periods 
being probably as efficient as the cold for longer periods; (c) certain 
varieties may escape infection; this may be due not to disease resistance 
but to differences in development at the time infection is most likely to 
take place; (d) the possibility of finding a resistant variety has not yet 
been exhausted; (e) no soil treatment will eradicate the disease, but 
sulphur at the rate of 900 pounds per acre applied broadcast reduces the 
amount of infection by S. subterranea . 
(11) Several types of dryrot follow 5 . subterranea . These, designated 
according to cause, are desiccation, plasmodium, and wound-parasite 
injury. The percentage of these secondary rots as found in nature 
in infected tubers varied from 30 to 73. 
(12) There is a close relation between certain soil types and the 
development of fungus. (See fig. 1.) From the type of soil and its drain¬ 
age it is possible to predict what the development of the disease will be 
in any particular field. 
(13) The dryrot due to a species of Phoma and other wound parasites 
is the most serious of the rots. After a comparison with earlier descrip¬ 
tions of various species of Phoma on the potato, the writers designated 
the species here discussed as “Phoma tuberosa 9 n. sp.” 
