WILT OP CUCURBITS. 219 



one additional vine has sickened naturally since my visit beginning August 22. This was all right 

 until recently having only a few blighted leaves and withering petioles in the center of the hill, but 

 now the whole of the big vine has wilted. 



There was no decided change in No. 10 until September 14, p. m. (after a rain which occurred 

 September 13). Then a whole leaf was found wilted suddenly. This was not the nearest leaf to the 

 one which I had infected and cut away, but the next nearest, i. e., the one on same side of the stem. 

 This vine had been examined at 8.30 a. m. and found all right. At 6.30 p. m. this whole leaf had 

 wilted. All the other leaves on the stem were upright. Turgid sections were cut from the petiole 

 of this wilted leaf and put into a moist place over night and next morning they bore the milk-white 

 drops on the cut ends. Other portions were put into alcohol. [These petioles were examined in 

 February, 1909, in thin sections under the microscope and bacteria were found in the vessels]. 



September 15, 10.30 a. m.: Five additional leaves were found wilted on this stem near the 

 original source of infection, two toward the center of the hill and three beyond the original source 

 of infection i .5 feet. Now the nearest leaf had wilted, i. e., the one on opposite side of stem. 



(n.) September 7: Many beads of the milk-white bacillus, which oozed from the cut end of 

 squash-stems were stirred up in water and three large squash-leaves were pricked with a needle, 

 not the one used for No. 9. These were tied with torn rags to identify them; No. 9, by white 

 cotton twine. On September 14, this plant showed 3 wilted leaves. 



POSSIBLE CARRIERS OF INFECTION OF B. TRACHEIPHILUS. 



The following insects, identified for me by Mr. E. A. Schwartz, were found on diseased 

 cucumber vines in 1 893 and suspected by me at that time of being agents in the distribution 

 of the wilt: Diabrctica vittata Fabr.; Diabrotica 12-punctata Oliv. ; Strigoderma pygmceum 

 Fabr. ; Chauliognathus marginatus Fabr. ; Epilachne borealis Kirby (lady beetle) ; Halticus 

 uhleri Giard = H. minutus Uhler (Hemipter) ; Coptocycla guttulata (not especially devoted 

 to the cucumber) . 



INOCULATIONS OF SEPTEMBER i, 1894.* 



One leaf on each of eight plants of Cucumis sativus, growing in the hothouse, was 

 inoculated with bacteria taken directly from white beads oozing on the cut end of cucumber 

 stems and squash-stems, the foliage of which was flabby or dying from the effects of the 

 wilt-disease. A sterile steel needle was touched to the ooze from a cucumber-stem and 

 twenty or thirty punctures were made in the center of the lamina of each of four healthy 

 leaves. The needle was then flamed and an equal number of pricks was made on the 

 blades of as many more leaves using bacterial slime from the ooze on a diseased squash- 

 stem. Plants i to 4 were inoculated from the cucumber; plants 5 to 8 from the squash. 

 The bacterial ooze from the cut cucumber-stems was so gummy and viscid that it could be 

 drawn out on the end of the needle in a delicate thread over a foot long. The bacterial 

 masses did not dissolve readily in water, not even after several hours, nor with vigorous 

 crushing and teasing. 



The temperature of the hot-house during the early part of the experiment was high, 

 as the following records show: Sept. 5, maximum 100 F. ; Sept. 7, at i h 50 p. m., 99 F. ; 

 Sept. 8, at noon, 98; Sept. 9, maximum 109; Sept. 10, at 2 h p. m. 104; Sept. n at 9 h 

 a. m., 72, noon 90; Sept. 13, at 9** a.m., 72, at noon 90. 



(i.) The first signs appeared the fourth day after inoculation and first in the pricked area. The 

 sixth day the whole blade of this leaf was affected and drooping, and its apex beginning to dry out. 

 All the other leaves remained healthy. The ninth day the blade of the leaf to each side of the pricked 

 one was wilted. On September 1 1 the leaf-blade next above and the one below the pricked one were 

 dry-shriveled, and the second leaf above showed change of color and wilt on one margin at the base 

 of the blade. Twenty-seven hours later one-half of the blade drooped and had changed to that 

 peculiar green characteristic of leaves wilted by the immediate presence of the bacteria. The other 

 side of the leaf was expanded and turgid. The disease progressed more slowly after the plant was 

 brought into the cooler laboratory (September 10). On September 13 the whole of the pricked blade 

 was wilted. On September 15 all of the leaves were wilted, 5 above and i below the inoculated 

 leaf. The sixteenth day after inoculation the whole stem was dry-shriveled except the hypocotyl 

 which was still turgid. 



"Those who wish to have etiologic proof without following all of the inoculations are advised to read only those 

 of July 1 6, 1896, beginning on page 276. 



