WILT OF CUCURBITS. 



269 



Fig. 75.* 



pricks to the margin. The ninth day (2 p.m.) the wilt involved most of the pricked side of the leaf 

 (fig. 75) and 25 hours later all of the pricked leaf had wilted but the petiole, while the other leaves 

 were normal. The eleventh day all the leaves had collapsed. The sixteenth day the vine had 

 shriveled to the ground. 



(277.) Cucumis melo var. dudaim. This was a small plant. Many pricks were made on the 

 blade of one leaf. The sixth day (10 a. m.) there was a slight wilt and change of color in the center 

 of the pricked area. Twenty-four hours later two-thirds of the pricked leaf was drooping. The eighth 

 day the pricked leaf was turgid with the exception of a wedge-shaped area extending from the pricks 

 to the tip and involving about one-eighth of the blade (fig. 75). The next afternoon there was only 

 a little increase of the wilt, but 25 hours later all of the blade 

 of the pricked leaf was wilted. The petiole was still turgid. 

 The blades of the first three leaves up now showed a slight 

 droop. The twelfth day all the leaves had collapsed and the 

 sixteenth day the vine had shriveled to the earth. 



(278.) Benincasa cerifera. Many pricks were made on one 

 of the leaf-blades of a small plant. On March 3 there were 

 no signs, but 24 hours later there seemed to be a slight droop 

 of the pricked portion. On March 5 there was no clear evi- 

 dence of the wilt, but the following afternoon (end of the eighth 

 day) there was change of color and distinct wilt. These 

 signs were confined to an area of about i sq. cm. from the 

 pricks to the tip, and the most of the pricked leaf was still 

 normal. Twenty-five hours later the wilt was spreading slowly 



in the blade of the pricked leaf. The twelfth day six leaves besides the pricked one (part above it 

 and part below) were wilted, some badly. Four days later the vine had shriveled to the ground. 



(279.) Watermelon (Citrullus -vulgaris). This was a small plant. Many pricks were made on 

 one leaf-blade. On March 3, at 10 a. m., there were no signs of the wilt, but 24 hours later the pricked 

 leaf had changed color and wilted from the pricked area outward to the tip, about one-third of the 

 leaf being affected. The following day the leaf had recovered its turgor except a very small wedge 

 at the tip beyond the pricks. The bulk of the pricked area seemed normal. The next afternoon 



During the next 25 hours there was a slow spread of the wilt and 

 change of color (whiter) in the blade of the pricked leaf. Two 

 days later about one-fourth of the pricked leaf had wilted and 

 dried out. The rest was normal. Up to the seventeenth day 

 there was no change. Four days later the whole of the blade of 

 the pricked leaf, which was a small one, had wilted. The petiole 

 and remainder of the plant were normal. 



(280.) Cucurbita calif arnica. Many pricks were made on one 

 leaf-blade which was 2 inches across. The leaf was almost exactly 

 the shape of a leaf of English Ivy. On March 3, at 10 a. m. there 

 was a slight wilt in the pricked area. Twenty-four hours later 

 about one-third of the pricked leaf had wilted and the following 

 morning fully one-half of the inoculated leaf had succumbed to 

 the wilt (see fig. 76). The next afternoon (March 6) the whole 

 of the pricked leaf had collapsed, also the first leaf below, the 

 neighboring cotyledon, and the first three leaves above. The 

 stem was turgid as were also the fourth and fifth leaves up and 

 the other cotyledon. Twenty-four hours later the signs were 

 much aggravated. The twelfth day the leaves had collapsed 

 including the petioles and the terminal part of the stem. The plant was now removed and put into 

 alcohol. On microscopic examination great numbers of bacteria were found in the vascular bundles 

 of the stem. 



(281.) Datura stramonium. This was a young thrifty plant. Many pricks were made on a leaf- 

 blade. A great quantity of bacteria were put into the leaf, but up to the twenty-first day the plant 

 was growing finely and there were no signs of the wilt. 



*FiG. 75. Left: Leaf of plant No. 276 (Cucumis melo var. dudaim), ninth day after inoculation with Bacillus 

 tracheiphilus, shaded part wilted. Right: Leaf of inoculated plant No. 277 (Cucumis melo var. dudaim) on eighth day 

 after Bacillus tracheiphilus was introduced by needle-pricks. The first wilt was a little earlier (central dark shading). 



fFiG. 76. Leaf of Cucurbita calif arnica (plant No. 280) inoculated with B. tracheiphilus. The needle-pricks were 

 made Feb. 26, 1896, and the wilt appeared in the deeply shaded part March 3. During the next two days it involved 

 over half the leaf-blade as shown by the lighter shading. The whole plant collapsed on the twelfth day. 



there was no decided increase. 



Fig. 76. f 



