WILT OF CUCURBITS. 243 



(9 2 . 93. 94. 95-) Tomato. Vines 8 to 10 inches high and pricked many times, 2 in stem and 

 2 in the blade of one leaf. 



No results. 



(96.) Cucumber (Cucumis sativus). This was a vine about 10 inches high with three good leaves. 

 The uppermost one was given many pricks. By the seventh day (9 a.m.) this vine had contracted 

 the wilt very decidedly on the terminal (pricked) portion of the leaf (apical two-thirds of the blade). 

 The preceding day there were no signs of the disease. The wilted portion of the leaf hung down 

 flabby while the rest of the plant was turgid and healthy except for a little superficial mildew. It 

 had taken six days for the disease to develop. It was plain from the different aspect of various parts 

 of the wilted portion that the wilt began in a V-shaped apical portion within the pricked area. By 

 2 p.m. the leaf blade was wholly flabby. The following morning the petiole was still rigid and normal. 

 At 9 a.m. of the eleventh day the whole of the small top above the pricked leaf was wilted. This top 

 was normal in appearance at 5 p.m. of the preceding day. The leaves below were still turgid as was 

 also the case at i h 3O m p. m. of the same day. The twelfth day (9 a.m.) the first leaf below the pricked 

 one was wilted. It was normal at 5 p.m. the preceding day. The following noon the first leaf below 

 had begun to dry out and the second leaf down was flabby. 



The fourteenth day the vine was brought into the laboratory and thin sections from the lower 

 part of the first internode below the pricked leaf were examined. The lower portion of the internode 

 was turgid but the upper part had begun to shrivel. The tissues examined were full of bacilli. There 

 was considerable variation in the breadth of the rods and some were much longer than others (samples 

 were put into alcohol). The bundles were much broken down so that a large cavity had formed. 

 None of the rods were motile. Five inches farther down (under the second leaf below the pricked 

 one, i.e., the leaf which had wilted the preceding day) the vessels of the bundles were gorged. The 

 tissue here was but little broken down and the parenchyma was nearly free from bacilli. A small 

 portion of the rods were actively motile. One and one-fourth inches farther down (in the hypocotyl) 

 the bacteria were confined to the vessels and a portion of them were motile. The bacilli strung up 

 from the cut stem 2 to 6 cm. when touched with a needle. Beef-broth-cultures were made December 

 24 from the interior of the stem where some of the bacilli were observed to be motile. Potato-cyl- 

 inders inoculated from one of these broths (December 27) yielded in four days a rather scanty, wet- 

 shining, white growth. 



(97.) Extra early Hackensack cantaloupe (Cucumis melo). This plant was 3 inches high and 

 had two small leaves besides the cotyledons, which were still green. Many pricks were made on the 

 first true leaf, the blade of which was about 1.25 by 0.75 inch. The eighth day (9 a.m.) the pricked 

 leaf was almost wholly flabby. It was normal at 2 p.m. the preceding day. The ninth day the vine 

 was wilted and was brought into the laboratory and examined microscopically. Many bacilli were 

 present in the vessels, but there were not so many as in 75 and 77, inoculated 4 days earlier, and 

 examined the same day. 



Remarks. This series of inoculations, and that of December 6, settled the fact that 

 the muskmelon disease is identical with that of the cucumber. I was in much doubt 

 about the squashes. Only one plant (No. 79) had contracted the disease while all the 

 squashes in this series and those in several other experiments (November 26 and December 

 6) refused to take the disease. I then interpreted these results as perhaps due to individual 

 or varietal resistance on the part of the squash-plants experimented with since subsequent 

 experiments performed in the same way gave positive results (see Nos. 215, 216, 217, 218, 

 and 220). 



No. 91 was very instructive in that it confirmed two suspicions: (i) The number of 

 motile bacilli increases as one gets farther and farther away from the point of infection 

 (i. e., among younger rods) ; (2) The organisms pass down the vessels a long distance ahead 

 of the signs. In this case the inoculated leaf was certainly removed within less than 22 

 hours and probably within 12 to 18 hours of the appearance of the first signs, while the 

 greater part of the blade of the leaf (at least five-sixths of it) was still apparently sound and 

 while the stem was still separated from the nearest wilted part by a distance of 5.5 cm. 

 Nevertheless the bacilli had already passed down into the stem, so that the progress of the 

 disease was but little if any slower than it would have been had the leaf not been cut away. 



