136 BACTERIAL DISEASES OF PLANTS 



Bunsen flame, or slowly in the flame of an alcohol lamp, so 

 as to singe the surface without cooking the interior. Place 

 the flamed part on a sterile surface (a strip of -glass or a clean 

 board passed repeatedly through the Bunsen flame, or the in- 

 side of a baked Petri dish) and cut crosswise with a red-hot 

 knife. If you have any doubt as to the sterility of the cut 

 surface, i.e., if you have accidentally touched it with your 



1 



. 



f; 



FIG. 68. FIG. 69. 



FIG. 68. Flagellate rods of Bacillus tracheiphilus stained by van Ermengem's 

 silver nitrate method: a, b, stained arid photographed by the writer in 1904. The 

 original negatives are X 1000, but the picture here shown has been made X 2000 

 to bring out the flagella more distinctly; c, stained by Mary Katherine Bryan, in 

 1915, and photographed by the writer. X 1000. 



FIG. 69. Agar poured plate smooth surface colony of Bacillus tracheiphilus 

 enlarged 25 times and photographed by transmitted oblique light to show internal 

 markings; 5th day, 1919. 



fingers or have dropped it, press the hissing hot knife firmly once 

 or twice for a moment or two on the cut end of the stem. Sur- 

 face organisms are thus excluded. Then squeeze the stem, 

 forcing bacteria from the unheated part to the cut surface for 

 your cultures. 



The slime of this organism within the vessels of the stem 

 is usually so viscid that plate cultures made from it frequently 

 miscarry. Along with this method, therefore, try a second, i.e., 



