250 



BACTERIA IN RELATION TO PLANT DISEASES. 



The inoculations were made under a newspaper-shade to keep off the direct rays of 

 the sun. The temperature was about 80° F. The vines which were planted March 1 2 were 

 in good condition and had several leaves besides the cotyledons. 



(150.) Muskmelon var. Shumway's giant {Cucumis melo). Many pricks were made in the 

 middle and upper part of a leaf 2.25 inches broad. The morning of the fourth day there was no trace 

 of the disease, but at 2 p.m. there was a distinct wilt covering about i sq. cm. near the apex of the 

 pricked leaf. It was then 4 days and 3 hours since the leaf was pricked. Twenty-four hours later the 



Fig. 67.* 



apical one-third of the leaf-blade had wilted and changed to a dull green verging on slightly yellowish 

 (at 9 a.m. the wilted area was not much greater than on the preceding day). The following day 

 (3 p.m.) two-thirds of the pricked leaf had wilted. The blade of the first leaf below was also flabby. 

 The internode between these two leaves was very short, i.e., not over 2 mm. The temperature in the 

 hothouse was over 90° F. The seventh day the blade of the first leaf above the pricked one had 

 wilted. It was separated from the latter by an internode only 2 cm. long. The second leaf below, a 



*FiG. 67. — Cross-section of extreme top of cucumber-vine No. 149 some days after infection with 5. tracheiphilus. 

 The plant was inoculated on the blade of a leaf by needle-pricks. The bacteria are a long distance from point of inocu- 

 lation and confined strictly to the bundles, all of which are invaded. Drawn from slide No. 205-2 . 



