WILT OF CUCURBITS. 



265 



two next below the pricked leaf. The rest were normal. The twenty-fifth day the apical 10 inches 

 including three internodes below the pricked leaf were dry-shriveled. The wilt was slowly extending 

 downward. Another big leaf-blade, the fourth down, had drooped the preceding day. Farther 

 down were five good leaves separated by long internodes. The stem was horizontal. The whole vine 

 finally shriveled to the ground. 



(246.) Cucumber. The eighth day (10 a.m.) there was wilt of the apex and margins of the pricked 

 leaf, extending outward mostly from the groups of pricks, involving loto 12 sq. cm. The leaf was 4 

 inches broad. There had been no wilt up to the preceding afternoon, therefore the period of incuba- 

 tion was nearly eight days. The tenth day the terminal three-fourths of the pricked blade had wilted 

 and was a dull yellowish green (it was more green than yellow but looked faded). The petiole and 

 remaining leaves were normal. By January 16 the blade of the pricked leaf had shriveled. The upper 

 half of the petiole was flabby and the extreme upper end was shriveling. The terminal six leaves (6 

 inches of stem) had wilted and also the blade of the first leaf down, the separating internode being 4 

 cm. long. The rest were normal. The twenty-first day the upper half of the vine had wilted. It was 

 now brought into the laboratory and by direct transfer four slant agar-cultures were made from it 

 (tubes i to 4, January 21, 1896) as follows: 



No. i from base of wilted part of stem (interior) ; 



No. 2 from interior of a young shriveling fruit 

 near the top of the vine; 



No. 3 from middle of wilted part of the stem 

 which had begun to shrivel; 



No. 4 from interior of stem not far from the 

 lowest external sign of wilt (in leaf) and where 

 the stem was sound externally but sticky within. 

 Nos. i and 4 yielded pure cultures of Bacillus 

 tracheiphilus. 



(247.) Squash. Groups of pricks were 

 made on a big cotyledon. Up to March 4 

 there had been no general wilt. The pricked 

 cotyledon was dead and the pricked part 

 was thicker than the rest as if from develop- 

 ment of cork-tissue. 



(248.) Squash. One of the cotyledons 

 was pricked. There was no result from 

 the inoculation. Even the cotyledons did 

 not wilt. There seemed to be cork in and 

 around the pricked area. 



(249.) Squash. The pricks were made 

 in one of the cotyledons. Up to March 4 

 (63 days) there were no general signs re- 

 sulting from the inoculation, although 22 

 days after inoculation there was a decided 

 wilt at the tip of the cotyledon which con- 

 tinued for several days extending very 

 slowly from the group of pricks outward. 



(250.) Squash. This vine was also pricked on one of the cotyledons but with no result. 

 March 4 the pricked part looked as if cork-tissue had been formed there. 



Remarks. In the cucumbers the bacterial wilt progressed upward faster than down- 

 ward, i. e., two or three times as fast. On the sixteenth day in the squash all the pricked 

 cotyledons were large, thick and green. One of the pricked cotyledons wilted at the tip 

 after 22 days. 



One of the cotyledons, collected March 4 (probably from 247 or 249) was afterwards 

 infiltrated with paraffin and sectioned. Bacteria were present in some of the bundles and 

 some of the latter were a little disorganized but not much. The impression one gets from 

 these sections is that the bacteria have multiplied in the vessels very slowly. A definite 

 corklayer was not made out. 



Fig. 74.* 



On 



*FiG. 74. Leaf of Cucumis salivus (plant No. 245) inoculated with B. Iracheiphilus and shaded to show progress 

 of wilt. The needle-pricks were made Dec. 31, 1895. First sign of disease appeared at apex of leaf on ninth day. 

 About 24 hours later wilt had extended as indicated by lighter shading. Drawn by the writer. 



