366 



BACTERIAL DISEASES OF PLANTS 



Fig. 281. — (irowinj^ shoot of Clapp's Favorite pear inoculated 5 days with a 

 pure culture of Bdcillus amylovorua plated from an apple twig. Bark blighted 

 and exuding drop.s of bacterial slime. Blight running out on petioles (a, a. a) 

 and on leaf-blade (6). Terminal leaves still green and turgid but in another 24 

 to 48 hours they would have become brown and shriveled. Lowest visible blight 

 at X. Internally the bacteria were traced under the microscope 3 inches farther 

 down the stem. May, 1915. The blue-black stripe of blighted bark and the pale 

 green of the normal part of the shoot photographed exactly alike, both with Ham- 

 mer's double-coated orthochromatic plates and with W. and W. panchromatic 

 plates. The eye-contra.st was finally obtained on the latter plate by using a green 

 color screen. 



