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 P. The vines which were planted March 12 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 



o 



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 mternode 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 

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



*F 1C. 67. Cross-section of extreme top of cucumber-vine No. 149 some days after infection with B. 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 



