284 BACTERIA IN RELATION TO PLANT DISEASES. 



now an enormous tangle of foliage and all the inoculated leaves which I could find were the seven 

 diseased ones. Signs appeared only in the pricked leaves. Several of these leaves were being gnawed 

 by the striped cucumber-beetle (Diabrotica vittata) but almost exclusively in the wilted, softened 

 parts. A week later the disease was progressing typically. The blade of the leaf which showed only 

 a tiny wilted area around the pricks on July 18 was now two- thirds wilted. Several of the inoculated 

 pla>nts now showed constitutional signs, i. e., other leaves up and down the stem were flabby or 

 wholly collapsed. One of these plants was brought in and examined under the microscope, bacteria 

 being found in the vessels. The bacteria also strung out one centimeter when the sticky cut surface 

 was touched with the finger. The plant was saved in alcohol. The disease had also been transmitted 

 to at least one healthy vine (one leaf) by the bites of the Diabrotica. This beetle was observed 

 feeding on the wilting leaves the week before and also to a slight extent, on the sound ones and one 

 of the latter now showed several square centimeters of wilt around the bitten part. 



(457-477.) About twenty leaf-blades belonging to several different plants were inoculated 

 directly from muskmelon petioles showing the sticky bacterial exudate. There was no definite result 

 until after the seventh day. On July 25 several plants showed typical signs in the pricked leaves. 



Remarks. This experiment adds another plant to the list of possible hosts. These 

 observations also tend to confirm the belief already expressed that the striped cucumber- 

 beetle prefers the wilted leaves and is consequently admirably adapted to spread this disease. 



The foregoing experiments were all made by the writer. Numerous additional ones, 

 partly by the writer and partly by his assistants (plate 14) have been made since this date, 

 but need not be mentioned here since they are not contradictory. Some of them have 

 already been referred to in the first part of the discussion of Etiology, where also are some 

 important observations on the distribution of the disease by Diabrotica vittata. 



Mention should be made, however, of some watermelon plants inoculated November 

 X 7> I 93- Of these, two plants (No. 530, variety Phinney's Early, and No. 534, variety, 

 Mountain Sweet) showed wilt of the inoculated leaf and were brought in and put into 

 alcohol on December 9 and 10. 



Nos. 526 and 528 (variety, Triumph), inoculated at the same time, showed secondary 

 wilt on December 5 and December 7, respectively. These also were preserved in alcohol. 

 Sections from the stems of the ones last mentioned show the presence of bacteria in all 

 of the vascular bundles. An attempt to plate out the organism miscarried. 



From the foregoing inoculations we may conclude that in wilting cucumbers the organ- 

 ism present in the tissues is sometimes B. tracheiphilus and sometimes B. tracheiphilus L 

 cucumis, whereas in squashes it is always or nearly always the first and more virulent strain. 

 This being true we might then expect some isolations from cucumbers to be infectious to 

 squash and others not, whereas all isolations from squash should infect both cucumbers and 

 muskmelons. 



I can not say whether there are any tangible cultural differences. In one test in litmus 

 milk at the end of two weeks the squash strain looked exactly like the check tubes, while the 

 cucumber strain was slightly darker. I cultivated out both on potato in typical form. 



EFFECT OF WATER ON CUCUMBER-WILT. 



Experiments in the greenhouse in May, 1895, showed that when water is withheld or 

 given sparingly the bacterial wilt becomes visible sooner than when the plants have an 

 abundance. If water be given to such diseased plants in abundance the leaves least wilted 

 will frequently become turgid again for a few hours. The same thing occurs in the field, 

 especially with squashes. 



VARIETIES ATTACKED. 



The writer has observed this disease or received reports of its occurrence in the follow- 

 ing varieties of cucumbers: White Wonder, White Spine, Long Green Japanese, Long Green, 

 Fordhook pickling, Telegraph, Large English (few seeded sort). 



