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 oxir 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 WILT 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 de fin itely, 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- 

 cheipMlus from 1 -week-old beef- agar cultures grown in large fiat 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 



