Nov. 8,1915 Dissemination of Bacterial Wilt of (Cucurbits 259 



collected in field No. i , where presumably they had hibernated. Within 

 a week several plants in i of the 2 cages in field No. i into which the 

 beetles had been introduced showed signs of wilt, starting from points 

 in the leaves gnawed by the beetles. Upon cutting ofT the stems the 

 typical stringing out of the viscid white bacterial slime was seen. Cul- 

 tures were made by the writer from one of these plants and subsequent 

 inoculations from these cultures into healthy plants again gave the dis- 

 ease. Other Avilted plants from the same cage were sent to Washington, 

 D. C, and from one of these Bacillus tracheiphilus was obtained and with 

 it successful inoculations were made in cucumbers in one of the Depart- 

 ment greenhouses by Dr. Smith. No signs of vsnlt occurred tit the 3 

 other cages in which beetles were placed, or, with one exception, in any 

 of the 46 other cages. 



Meanwhile in both fields the wilt was beginning on plants between 

 the cages. At first the wilt appeared only on a plant here and there, and 

 then gradually extended throughout the two fields until no portion was 

 entirely exempt. In the two fields together there were in the neighbor- 

 hood of 1,200 hills of cucumbers exposed to attack of the beetles. The 

 cages in field No. i extended approximately a quarter of a mile through 

 the field at equal distances and in field No. 2, which was about two-thirds 

 as large, they were spaced closer. There was a check plot contiguous to 

 each cage. The approximate number of cases on the plants in field 

 No. I during the three months was 600; in field No. 2 it was 200. No 

 counts were made after September i, owing to the appearance of the 

 cucumber mildew (Plasmopora cuhensis). 



In all these cases of wilt in the exposed (uncovered) plants, infection 

 was clearly seen to have started from beetle injury. Careful record was 

 kept throughout the season of every hill and plant showing wilt, and 

 although between the cages the disease was everywhere present the plants 

 within the cages were strikingly free from the disease. The plants in 

 these 50 cages were examined every day from planting time (June 5-6) 

 until September i. In one cage where beetles were not liberated, wilt 

 was noted just starting in the tip leaf of one plant at a point gnawed by 

 a beetle. A careful search in this cage disclosed a striped beetle, which 

 was summarily disposed of. Microscopical examination and cultures 

 from the lower part of the stem failed to disclose any bacteria, showing 

 that the wilt in this case could not have come from the soil and must have 

 been brought in by the beetle, which probably entered through a crack 

 due to warping of the boards. Careful search failed to disclose any 

 further beetle injury within the cage, and, after the removal of the beetle 

 and the one wilting plant, no further signs of the disease appeared therein 

 during the season. With this exception and that of the above-mentioned 

 I cage into which the beetles were purposely introduced, not a case of 

 wilt occurred in any of the 50 cages during the entire season. 



