WILT OF CUCURBITS. 235 



November 20) diluted with four times its bulk of sterile water. The insects were allowed to feed 

 until 1 p.m. Then the squash was removed and the beetles allowed to crawl over the bottom, top 

 and sides of the moist infected glass dishes. At 4'' 30'" p.m. they were turned loose in the insect- 

 cage. The next morning most of the beetles were at the top of the cage and had eaten but little. 

 At 1 1" 30"' I removed nearly all of the beetles and put them in dry, clean, glass dishes in order to 

 starve them. They were left thus without food for 24 hours. I then sprayed the beetles and the top, 

 bottom, and sides of the glass dish with the contents of a tube of potato-broth (culture of November 

 20) mixed with a tube of sterile potato-broth to which an equal amount of sterile water was then added. 

 The potato-broth-culture was faintly clouded with rolling clouds when shaken. It was examined 

 in a hanging drop and one in perhaps 20 to 50 of the rods on the edge of the drop were found to be 

 motile. At 1'' 30'" p.m. the dish was uncovered in the insect-cage and the beetles turned loose again 

 after wetting down the pots and sand on the bench, inside and around the cage. Four days later 

 (the twenty-sixth day from the beginning of the experiment) there was no trace of the wilt. Some 

 of the Diabrotica vittata were feeding very slowly but most of them not at all. On the forty-first day 

 4 out of 5 leaves on one of the vines were wilted, the lowest leaf and the upper leaves. These leaves 

 had been all right in appearance the preceding day. Diabrotica vittata was still in the cage: 1 or 2 

 had begun to eat a little of late but most of them were hibernating. 



On another plant in this cage the third and fourth leaves up yellowed and shriveled in December 

 from serious gnawings but without suspicious signs. Sometime between January 1 and 4 the second 

 leaf up wilted with signs regarded as suspicious. On the morning of January 4, the fifth leaf up showed 

 a decided droop, although the earth was moist enough. Twenty-four hours later 4 small leaves above 

 the fifth leaf were wilted. The stem was green and turgid but there were no healthy leaves on the 

 plant. The stem was now cut open and examined in several places, but no bacilli were found, and 

 the cause of the wilt of the leaves remained uncertain. Possibly bacteria might have been discovered 

 in the leaves. 



(38 a, b, c.) Three pots containing 3 vines, 6 to 8 inches high, with 12 good leaves besides the 

 cotyledons, were placed in an insect-cage at 1 p.m. with 15 or 20 specimens of the infected cucumber- 

 beetle (Diabrotica vittata). The beetles began to feed at once and all but one or two were taken out 

 at 5 p.m. Holes had been gnawed in the leaves of each vine. The next morning the vines appeared 

 normal, only a trifle gnawed. The second day the vines looked very thrifty. The twentieth day 

 more specimens of Diabrotica vittata were sprayed with a pure potato-broth-culture (tube 2, Novem- 

 ber 20) and introduced into the cage. The next morning the beetles were at the top of the cage for 

 the most part and had eaten but little. At 11'' 30'" a.m. I removed nearly all the beetles, starved 

 them for 24 hours, sprayed them again (with potato-broth-culture of November 20 see 37a, b, c) 

 and turned them loose in the cage as in the preceding experiment. The twenty-sixth day there was 

 no trace of wilt. Most of the beetles were not feeding at all but some were eating slowly. The forty- 

 first day there were still no signs. 



(39 a and b.) A pot containing two vines, 16 and 17 inches high with 7 good leaves besides the 

 cotyledons, were placed under a bell-jar after spraying both surfaces of each leaf. About 4 p.m. 6 or 

 8 cucumber beetles (Diabrotica vittata) were turned loose on them. The next morning all the beetles 

 but two were removed. The leaves were considerably gnawed. One of the remaining beetles was 

 removed the afternoon of the second day and the other the third morning. The twentieth day there 

 were no traces of wilt. (No further record.) 



(40.) One vine 4 inches high with 2 green cotyledons and 3 good leaves was placed under a bell- 

 jar. About 20 specimens of Diabrotica vittata were introduced at 4 p.m. All went to the top of the 

 bell-jar. The next morning all were removed. The leaves were riddled by bites. The seventh day 

 the upper half of the upper leaf hung down flabby but without change of color. This leaf had been 

 gnawed on both margins. Two days later (noon) 2 of the gnawed leaves showed very suspicious 

 signs and the next morning the local wilt and change of color was unmistakable. Both leaves cer- 

 tainly had the bacterial disease. This vine had been sprayed with a pure culture of Bacillus trachei- 

 phihts. The beetles were placed on it November 2, consequently the first unmistakable signs appeared 

 in 9 days. On the tenth day at noon the leaves were more wilted. All the others were turgid although 

 one was as badly bitten. At 4 p.m. a third leaf had changed color and wilted. This had been only 

 slightly bitten. Evidently there were three distinct infections and perhaps more. On the eleventh 

 day the three infected leaves hung down limp. On November 16 the vine had partly damped off 

 at the surface of the earth. This was due to being watered too heavily the preceding day. (It was 

 still under the bell-jar. ) It had been going long enough to give striking results, however. The petioles 

 were still turgid. On November 17, the vine was brought into the laboratory and examined micro- 

 scopically. Bacteria were found in the vessels, and samples of the plant were saved in alcohol. 



Remarks. Up to December 10 only four good cases appeared and all were upon 

 sprayed plants standing under the bell-jars. Three were on plants punctured by the squash- 



