BACTERIAL WILT OF CUCURBITS. 13 
March 26, 1917. Some soil in a greenhouse bed was inoculated to the consistency 
of thin mud with a thick, milky suspension of wilt bacteria. After 12 hours 10 young 
cucumber plants were thoroughly wet down with a tap-water suspension of this soil 
and the leaves all needle punctured. No wilt occurred in any case, although the 
six control plants inoculated with the original bacterial suspension promptly wilted. 
For some reason the bacteria placed in our greenhouse soil have 
not retained their power to infect. This might be due to a too-great 
dilution of the bacteria, to their adsorption by the soil particles, or 
to injury or death from other antagonistic organisms, or from toxic 
substances in the soil. This phase of the problem is being further 
investigated. 
DO INSECTS BRING WELT FROM THE SOIL TO THE PLANT? 
Although cucurbit plants do not contract wilt directly from the 
soil under field conditions, the question was raised whether the wilt 
organism might not be brought up from the soil on the bodies of 
insects and introduced into wounds made by insects or other agencies. 
Such a method of infection is against conclusions drawn from careful 
field observations during several seasons in many localities. Fur- 
thermore, insects other than the Diabroticas have in all our tests 
failed to transfer the disease; and mechanical injuries to the vines 
resulting from storms, cultivation, and other causes in fields badly 
infested with wilt during the current and preceding seasons have 
shown no relation to wilt infection. However, for the sake of clear- 
ing up this point definitely, the following greenhouse and field exper- 
iments were made. 
October 15, 1916. The soil in a large greenhouse bed was divided 
into eight compartments, each approximately 4 feet square, with solid 
board partitions at the base extending 2 feet into the soil and each 
compartment covered with 18 mesh wire netting over a skeleton 
frame (PI. III). The soil was sterilized for one hour at 15 pounds 
steam pressure by the steam-pan method, to kill all insects present. 
This sterilization was repeated one week later to make the result 
doubly sure, and care was taken that every part of the soil was 
reached. The soil was allowed to stand three weeks and was then 
raked over with sterilized tools and thoroughly wet down in seven 
compartments with a heavy tap-water suspension of Bacillus tra- 
cheipliilus from 1 -week-old beef-agar cultures grown in large flat cul- 
ture flasks. The soil in compartment 4 was sprinkled with tap water 
only and held as a control. In the inoculation suspension 10 differ- 
ent isolations of the wilt organism were used. Before inoculation of 
the soil the virulence of this suspension was proved by needle-prick 
inoculations in the leaves of 13 potted cucumber seedlings, all of 
which promptly wilted. Arlington White Spine cucumber seeds were 
