WILT OF CUCURBITS. 



223 



(15.) The pricked leaf was the first to show signs of the disease. They were noted the eleventh 

 day after inoculation, but as the droop did not seem to proceed from any particular spot I was in 

 doubt as to its cause. The thirteenth day the leaf above and the one below the inoculated leaf showed 

 wilt. The fourteenth day they began to shrivel, the whole blade of the inoculated leaf was dry- 

 shriveled, three additional leaves farther up the stem also showed a decided droop, and a fourth one, 

 still higher up, a slight flabbiness. The rest of the leaves above and below were turgid and showed no 

 sign of the wilt. The disease was moving up faster than down, as in some cases previously recorded. 

 The following day (October 4) three additional leaves nearer the tip were wilted and one more 

 toward the base making eleven in all, to wit: eight above the inoculated leaf and two immediately 

 below it. The remaining basal leaf and the four leaves at the tip of the vine were still turgid. 

 Two of the four noted as having wilted the previous day (the two nearest the point of infection) 

 were then shriveling. The plant was now brought into the laboratory. The seventeenth day the 

 wilt showed on the lowest leaf. All the leaves farther up as well as the stem in places had begun to 

 shrivel. When segments of the stem were examined microscopically, the vessels were found to be 

 full of the bacteria, which varied in size noticeably and looked much larger than usual (involution 

 forms?). In the primary vessel parenchyma were many destructive lesions. The bacillus was also 

 found in a small, green fruit, hanging midway on the stem and looking sound externally. Here it 

 was confined to the bundles in the outer ring from which it slowly oozed on cross-section. The next 

 day (October 7) the cut surface over the affected bundles was covered with a milky and very viscid 

 bacteria] slime which strung out on the tip of a needle a distance of 40 cm. (15.75 inches). The milky 

 beads which oozed from the bundles of the cut fruit yielded a pure culture of B. tracheiphilus. On 

 October 17 a potato cylinder inoculated October 7 was covered, except its edges, with a thin, gray- 



Fig. 58.* 



white, wet-shining layer which followed the irregularities of the surface of the steamed potato but 

 was otherwise smooth, and was almost exactly the color of the potato but easily distinguished by 

 its wet-shining surface. Thirteen days later there was no change in the appearance of this culture, 

 except that it had spread over more of the potato. For the condition of this vine on October 4, see 

 accompanying diagram (fig. 58). 



Inoculations of October i, 1894. 



Two sets of inoculations were made on Cucumis sativus in the hothouse. One plant (18) 

 was infected with a gray-white, wet-shining organism from a potato culture of September 

 23 made from tube 1, September 17, which was inoculated from vine 2. The other two 

 (16 and 17) were inoculated with a bacillus (examined in hanging drop), forming a cloudy 

 growth in a fermentation tube of saccharose bouillon. This saccharose bouillon was inocu- 



*Fig. 58. Diagram showing condition of cucumber-vine No. 15 on Oct. 4, 1894; a, leaf inoculated on blade Sept. 

 19 by needle-pricks. First signs of disease appeared on Sept. 30 in pricked leaf: (1) Position of leaves which showed 

 secondary wilt on Oct. 2; (2) position of leaves which wilted on Oct. 3; (3) position of leaves which showed first signs 

 of wilt on Oct. 4. Z and M, leaveswhich wereturgid on Oct. 4. Z, which was the last leaf to succumb, drooped on 

 Oct. 6. F , a small fruit from the interior of which B. tracheiphilus was obtained in pure culture. Y, lower nodes from 

 which leaves disappeared naturally owing to small size of pot. 



