256 BACTERIA IN RELATION TO PLANT DISEASES. 



specimens of Diabrotica vittala were turned loose on them after the insects had been thoroughly 

 sprayed with the dilute broth and left to crawl about in the infected liquid half an hour. Many of 

 the leaves were already whitish on the margins and there were brown spots on the others and some 

 mildew (Eryslphe chicoracearum). July 16. The experiment failed. 



(196 a to g.) Cucumbers. Three pots containing seven plants much like those just described 

 were placed in an insect-cage. The lower leaves were injured more than the preceding and there were 

 large dead patches on the margins of some of the leaves and others were becoming whitish probably 

 from malnutrition. The soil outside and in was thoroughly wet down and the wire of the cage was 

 also wet so as to keep the air inside moist for the next 24 hours. The surface soil of the pots was then 

 slightly sprayed with the dilute broth and also, thoroughly, every part of each plant stems, young 

 fruits, open flowers, old and young leaves (both sides), and the buds and leaf axils, so to as cause the 

 disease if possible. The infectious material was from the same tube as that used for 195. Almost all 

 the aphides were removed but not quite all. The broth used for infection was not very satisfactory . 

 It was not swarming with rods, i. e., there was only here and there one in the hanging drop although 

 of course where so much fluid was sprayed on, the aggregate number of rods was large. The inocu- 

 lations were made on a cloudy, cool, rather damp afternoon. The plants in this cage were to be held 

 as a check on the preceding. July 16. There was no result from the inoculation. 



INOCULATIONS OF JUNE 15, 1895. 



Squash-vines (Cucurbita sp.) and pumpkin-vines (Cucurbita pepo) were pricked and 

 inoculated at noon with sticky bacterial ooze directly from the interior of a petiole of the 



inoculated cucumber-vine 190. Two cucumbers (Cucumis 

 sativus) were inoculated as checks. The day was sunny 

 and hot. There is no statement as to the number of needle- 

 punctures, but only that the checks were inoculated in the 

 same way as the others. 



(197.) Cucumber. This vine was inoculated as a check. No 

 record of where inoculated but undoubtedly on some leaf -blade. 

 The fourteenth day (noon) half of the foliage had collapsed. Two 

 days later the vine was brought into the laboratory and examined. 

 From the cut end of the stem there oozed a sticky white bacterial 

 slime, drawing out in slender threads, and a microscopic exami- 

 nation showed that the vessels contained great numbers of a 

 bacillus morphologically like B. tracheiphilus. 



(198.) Squash. Two terminal small leaves were pricked. 



No result. 



(199.) Cucumber. This vine was also inoculated as a check. On July 9 some of the leaves were 

 wilted. It was brought in and examined microscopically. The vessels were found to be full of 

 bacilli of variable size (fig. 70.) 



(200.) Squash. The third leaf from the tip was pricked and inoculated. 



No result. 



(201.) Pumpkin. The stem was pricked. 



No result. 



(202.) Pumpkin. The stem was pricked. 



No result. 



(203.) Squash. The stem was pricked. 



No result. 



(204.) Pumpkin. A leaf was inoculated. 



No result. 



Remarks. The squash-plants and pumpkin-plants were kept under observation for 

 38 days. The squashes were grown from seeds planted March 12. Here again cucumbers 

 contracted the disease while squashes and pumpkins resisted it. 



*FiG. 70. Bacteria, especially aberrant forms, from interior of cucumber-vine No. 199, inoculated with B. 

 tracheiphilus. The common forms are 1.8 to 2.5 by 0.6 to 0.7*1- About i :ioooori : 2000 is much larger, but transition 

 forms were observed. Rarely one with a distinct capsule was seen. Cover-glass preparation stained by van 

 Ermengem's nitrate of silver method. July, 1895. 



