WILT OF CUCURBITS. 253 



they were lower down than the blade of the second leaf which was wilted. The tenth day the petioles 

 were still rigid but all the blades were drooping except of one cotyledon and on the tiny leaves of the 

 bud which were not transpiring much. The fourteenth day all the leaves were wilted. The petioles 

 and stem were still bright green and turgid. 



The plant was now examined microscopically. The vessels were gorged with the bacillus and 

 there was an extensive degeneration of the spiral vessels and of the primary vessel-parenchyma 

 (slide 210). Portions of this vine were preserved in three different ways to determine the best way 

 to fix the bacilli and slime in the vessels without shrinkage of the tissues of the host: (1) The first 

 lot was put directly into absolute alcohol which began to remove the chlorophyll inside of two hours 

 so that the lower half of the fluid was decidedly green; (2) 75 per cent alcohol which fixed the slime 

 and in two hours had not withdrawn any chlorophyll; (3) 50 per cent alcohol which did not fix and 

 was worthless. In the 50 per cent alcohol the bacilli oozed out within 2 hours in quantity and formed 

 a milky slime in the bottom of the bottle and all over the ends of the segments. There was not 

 much choice between the effect of absolute alcohol and 75 per cent alcohol. 



(168.) Cucumber var. White Wonder. About 20 pricks were made in the center of a leaf-blade 

 about 2.5 inches broad. The pricks were all in an area not over 5 mm. in diameter and each side of 

 the midrib. The eighth day there was no trace of the disease but the following day (11 a.m.) the 

 wilt appeared over an area 5X15 mm. extending from the pricked part outward toward the tip along 

 a side vein. The tenth day there was still no wilt except on the pricked leaf. The narrow oblong 

 area which appeared wilted the day before had now dried out and much fresh tissue was involved 

 in the wilt, about one-sixth of the whole leaf being affected, i. e. , each side of the midrib to the apex 

 and also downward over half-way to the base of the blade. The seventeenth day the vine was 

 brought into the laboratory and dissected. The leaf-blades were all wilted some days before. With 

 the exception of the lowest petiole which was wilted and somewhat yellow at the tip, the petioles were 

 all green and turgid. The stem was turgid and normal in external appearance. There was no rot 

 at the base of the plant. The interior of the vine was full of bacilli. 



No. 168 was the fourth and last check against the squash and pumpkin inoculations, none of 

 which had given any positive results. The internodes of this vine were cut into short lengths and 

 put alternately into two bottles. Those in one were covered for 22 hours with 1 per cent tri-nitro- 

 phenol dissolved in absolute alcohol; the others were put for the same time into absolute alcohol 

 saturated with mercuric chloride. The former proved the best fixative. 



(169.) Tomato (Lycopersicum esculentum). About 20 pricks were made in a green fruit about 

 one inch in diameter. Some of the pricks were shallow and some were deep. Many thousands of 

 the bacteria were put in. The fourth day the fruit was one-third larger. There was a very narrow 

 rim of dead tissue about the pricks and beyond this a narrow ring of tissue which was darker green 

 than natural. This second ring was not over 0.4 mm. broad. On May 9, 24 days after inoculation, 

 the tissue around the pricks was slightly sunken. The immediate border, 0.2 mm. in width, was 

 dead; beyond this for a short distance (0.5 to 1 mm.) the tissue was a little darker green than natural. 

 There were no other signs. The fruit had become three times as big as when pricked and the other 

 fruit on the cluster (earlier set) was ripe. On May 14 the inoculated fruit was ripe. The second 

 ring referred to above, ripened more slowly than the rest and was still greenish. The fruit was sound, 

 normal and well flavored. 



(1 70.) Tomato. A green fruit about an inch in diameter was pricked 12 times and a great many 

 bacteria were inserted. There was no result from the inoculation. The fourth day it resembled the 

 preceding. On May 9 the four fruits in the cluster were all growing finely. The pricked one was 

 exactly like 169 at this date. On May 20 it was fully ripe and was picked and eaten. It was entirely 

 sound. The only result from the pricks was death of ruptured cells and retarded ripening just around 

 the track of the needle. 



Remarks. The following note of June 10, 1895, may be of interest in connection with 

 the observations on Nos. 169 and 170. 



Two small green tomato fruits pricked with a pin some weeks ago have become darker 

 green around the pricks just as did those previously inoculated with Bacillus tracheiphilus. 

 Apparently the phenomenon is the reaction of the plant against the puncture and not against 

 the bacteria. 



This experiment confirmed the earlier ones. Cucumber and muskmelon were found 

 susceptible to the culture used while squash, pumpkin and watermelon were resistant. All 

 of the former and none of the latter contracted the disease. 



