22O 



BACTERIA IN RELATION TO PLANT DISEASES. 



(2.) The first signs appeared the fourth day after inoculation, the pricked area being the first 

 part to show the wilt. The fifth day the inoculated leaf was cut away at the extreme base of the 

 petiole. The progress of the wilt had been that shown in the sketch (fig. 56). The wilt did not extend 

 more than 0.25 inch below the pricks and the petiole was 2.5 inches long. It was hoped, therefore, 

 that the bacteria were removed with the leaf and that the plant as a whole, would remain free from 

 the disease. Such was not the case. On the twelfth day one or two leaves showed a slight tendency to 

 wilt. The next day the wilt was more decided although the soil had been watered copiously. On the 

 fourteenth day 6 leaf-blades were wilted and drooping, i below the removed leaf and 5 above. The 

 sixteenth day the plant was dissected and its vessels found to be gorged with bacteria. All the leaves 

 were shriveled, but the stem was still green and turgid. The bacterial ooze from the cut stem was 

 viscid and strung out in delicate cobwebby threads when touched, the same as the slime from which 

 the plant was inoculated. The organism was cultivated out of the interior of this plant and gave 

 rise to a long series of cultures of Bacillus tracheiphilus. Stem, dried for herbarium. The cultures 

 referred to were direct ones (Beef-broth tubes Nos. i and 2, September 1 7). These were feebly clouded 

 on September 19, and looked alike. Each contained an actively motile bacillus. Tube i was used 

 for inoculating plants 12 to 15; the organism was also cultivated out of it on slant agar, yielding 

 typical colonies. Nine of these colonies when transferred to as many steamed potato cylinders 



yielded in 6 days typical gray-white, 

 wet-shining, thin, sticky growths, 

 scarcely distinguishable in color from 

 the potato itself; 6 other cultures 

 were made on September 17 direct 

 from the interior of this vine 3 

 slant agar and 3 potato. Two agars 

 yielded nothing, the other, a single 

 thin-edged, smooth, wet-shining, 

 slow-growing, white colony (diam- 

 eter 2 mm. after 15 days). The 3 

 potato tubes yielded typical growths 

 of B. Irachcipliilus, one of which was 

 transferred to a tube of slant agar 

 on September 23. 



(3.) The pricked area was the 

 first part to show signs of the disease, 

 which it did on the fourth day after 

 the inoculation (noon or earlier) . On 

 the fifth day at 3 p. m., the inocu- 

 lated leaf was cut away at the ex- 

 treme base of the petiole (the petiole 

 was preserved in alcohol along with 

 that of No. 2, and portions of the 

 wilted parenchyma of each leaf). 

 The inoculated leaf resembled that 

 of plant 2 very closely, about one- 

 third of the apical portion being 

 wilted. The wilt did not extend 



more than one-fourth inch below the pricks and the petiole was nearly twice as long as in No. 2. The 

 disease was not cut out, however, by removal of the affected leaf. Like plant 2 the vine showed some 

 signs of disease on the twelfth day and unmistakable ones the thirteenth day. On the fourteenth 

 day 3 leaf-blades, i below and 2 above the removed leaf, were wilted and drooping. On the nine- 

 teenth day after inoculation the plant was about 80 cm. long. All of the leaves to the extreme tip 

 had wilted. The stem was still normal in color and turgid except for a slight shrinking just under 

 the insertion of the inoculated leaf. The vine was now cut and examined in many places. The 

 bundles were gorged with bacteria, nearly every vessel being full of what seemed under the micro- 

 scope to be one kind of organism. Part of these bacteria were motile. As in other vines of this 

 series, the number of motile rods increased toward the tip of the plant, i. e., at more and more 



*Fic. 56. Leaf of Cucumis salmis (No. 2) inoculated with B. tracheiphilus by needle-pricks and shaded to show 

 progress of wilt. First signs on fourth day (Sept. 5): /, 6 a. m.; 2, noon; j, 4 p. m.; 4, Sept. 6, 3 p. m. On this date 

 the leaf was cut away at its base, but the bacteria had already passed down vessels of the leaf-stalk and had entered 

 the stem as shown by subsequent events (petiole 2.5 inches long). Pure cultures yielding a long series of successful 

 inoculations were afterward obtained from interior of the stem of this plant. Drawn by the writer. 



Fig. 56. 



