DISEASES DUE TO BACTERIA 123 
a glass jar. Microscopic examination of diseased stems 
shows the large vessels of the wood to be completely 
filled with an incalculable number of bacteria, and the 
wilting is thus brought about by the choking of the 
conducting system. 
The causal organism was first described by Dr. E. F. 
Smith (46), who named it Bacillus tracheiphilus. 
The disease is by no means common in this country, 
but spasmodic outbreaks have occurred with serious 
results. In America the disease is widespread, and 
attacks cantaloupes, cucumbers, pumpkins, and squashes, 
but not water melons, the cucumber being by far the most 
susceptible of these plants. The disease has been found 
to occur in varying intensity from season to season, at 
times only an occasional wilted plant being reported, 
while at others 70 to 95 per cent of the crop has been 
destroyed. Rands and Enlows (41) found that the 
percentage infection and the rate of progress of the 
disease were not determined by weather conditions, 
but were related intimately to the vigour of the plant 
and to the prevalence of cucumber beetles present at 
the time. They demonstrated that the bacteria do not 
winter in the soil in America, and found no evidence 
that they were carried by the seed. Infection does not 
take place through the stomata or breathing pores of 
the plant, but depends upon the introduction of the 
causal bacteria into the inside of the plant by some 
suitable agency, which might well be of the nature of 
an insect. 
In America the striped cucumber beetle (Diabrotica 
vittata) and the twelve-spotted cucumber beetle (D. 
duodecimpunctata) have been shown to carry the disease 
from plant to plant during the growing season, and are 
probably the only means by which the disease is spread 
under natural conditions. Under glasshouse conditions 
in this country it is probable that the cucumber wood- 
louse is instrumental in disseminating the disease. It 
has invariably been found that plants which have received 
