WILT OF CUCURBITS. 239 



November 19 (reinoculated November 21) from potato broth No. 2, November 17, which 

 was inoculated from the interior of vine No. 24. The squashes were crowded, two together, 

 in 4-inch pots. 



(57.) Summer Crookneck Squash (Cucurbita sp.) This vine which was growing rapidly was 

 pricked on the first leaf. The seventeenth day the cotyledons were shriveled but there was no result 

 from the inoculation. The thirty-sixth day the vine had lost all its leaves and begun to shrivel. Sec- 

 tions were examined under the microscope but there was no trace of bacteria in the vessels of the 

 stem. 



(58.) Summer Crookneck Squash. The first leaf of a rapidly growing vine was pricked. There 

 was no result from the inoculation. The cotyledons shriveled and after a time (36 days) the vine 

 lost all its leaves and began to shrivel. No trace of bacteria was found in the vessels of the stem on 

 microscopic examination. 



(59-) Winter Squash var. Improved Hubbard (Cucurbita sp.) . The first leaf was pricked. 

 The vine was growing rapidly. There was no result from the inoculation. The seventeenth day the 

 cotyledons had shriveled naturally. Two months after infection the vine was brought into the 

 laboratory and the stem examined in several places. It was green and long and had lost most of its 

 leaves except those toward the apex, where they were normal but small. There was no trace of 

 bacteria. The plant was kept in a small pot. 



(60.) Winter Squash var. Improved Hubbard. The first leaf was pricked. This vine behaved 

 like No. 59. After a time it lost nearly all its leaves but no trace of the wilt appeared. The stem 

 which was still green was examined in several places on January 28, but there was not a trace of 

 bacteria. 



(6 1.) Potato (Solatium tuberosum). This was a small shoot about 3 inches above the ground. 

 Two small leaves were pricked. There was one other leaf lower down. 



Another shoot in the same pot was held as a check. The inoculation 



was without result. In three days the inoculated shoot trebled its size. 



The pricks were now open places and on both surfaces of the leaf there 



was a curious, pale greenish, ringed elevation surrounding each prick and Fig. 64.* 



consisting of an outgrowth of cells from the edge of the wound (fig. 64). 



February 6, the vine was wholly shriveled. It was brought into the laboratory and examined 

 for bacteria but none were found. 



INOCULATIONS OF DECEMBER 6, 1894. 



Five potato, 6 tomato, 7 muskmelon, and 5 squash vines were inoculated in the hot- 

 house with Bacillus tracheiphilus (cucumber-strain) from a motile potato-broth culture 

 (tube 2, December 3). A small steel needle was used to make the punctures. 



(62.) Potato (Solanum tuberosum). Two shoots of a plant 7 inches high were inoculated. On 

 one the stem was pricked, on the other two leaves were pricked. The plant became diseased but 

 not as a result of the inoculation. The foliage was stunted and finally became dry-shriveled. By 

 the twenty-second day the vine was very sickly, both shoots equally so, and without apparent cause. 

 The roots looked healthy and the disease did not seem to have spread from the pricks on stem or 

 leaves. On microscopic examination no traces of bacteria were found in the tissues bordering 

 the wounds. On this date the other inoculated potato shoots were twice as large and looked healthy. 



(63.) Potato. Two of the three shoots of a vine 9 inches high were inoculated. One was pricked 

 on the stem, the other on two leaves. For a time the vine grew rapidly but 40 days after inoculation 

 the tops of the three shoots were dead and shriveling and none of the foliage was vigorous. This 

 weakening had been gradual and had proceeded from the top of the shoots down and not from the 

 pricked parts. The shoot pricked on the stem was now carefully examined microscopically at top 

 and bottom but no fungi or bacteria were present. The pricked portion was sound. That the dis- 

 ease had not arisen from the inoculations was shown by several facts: (i) It did not begin in the 

 pricked parts; (2) no bacteria were present in any part of the stem, at least not in that part which 

 was badly diseased and wilting; (3) the shoot which was not pricked at all and the one which was 

 pricked only on a leaf were as badly affected as the one pricked in the stem. Subsequently the plant 

 was taken out of the pot, the dirt washed off and the root system examined. There was no sign of 

 fungi or decay. The mother-tuber was not rotten or black and it had preserved its original form 

 and appearance. Sections treated with chlorzinc iodide showed that most of the starch grains had 



*Fic. 64. Diagrammatic section of a potato leaf, plant No. 61, showing new tissue formed about lips of needle- 

 wound. Third day after inoculation with Bacillus tracheiphilus. 



