38 



THE FUNGI WHICH CAUSE PLANT DISEASE 



B. amylovorus (Burr.) De Toni. (Group number 221. — .) 



Bacillus in broth, 0.9-1.5 x 0.7-1.0 fi, longer when older. 

 Gram positive; no capsule; flagella several; no spores; broth 

 clouded, pellicle slight. Gelatine shows slow, crateriform lique- 

 faction. Agar, buried colonies white, surface 

 colonies elevated, circular wet-shining, margin 

 irregular. Milk coagulated in three-fourths of 

 a day, later digested to a pasty condition. 

 Opt. 25-30°. T. D. P. 43.7°, 10 min. Faculta- 

 tive anaerobe. Indol produced; no gas; no pig- 

 ment. 

 Bacteria were noted in blighted pear twigs by 

 Fig. 23.— b. amyio- BuTrill in 1877.*'' *' In 1880 he ^* demonstrated 

 rn"'by'"fisifon? *^^ communicability of the disease by intro- 

 After whetzei ducing the bacterial exudate into healthy pear 

 trees as well as into apple and quince trees. 

 This constitutes the first case of plant disease definitely at- 

 tributed to bacteria. Burrill's results were confirmed by Arthur 

 in 1884 *^ by one hundred and twenty-one puncture 

 inoculations, using the exudate, also a bacterial 

 suspension from diseased twigs. He further demon- 

 strated the susceptibility of Juneberry and haw- 

 thorn. Usually the disease appeared about a 

 week after inoculation. Attempted raspberry and 

 grape inoculations failed. 



Arthur placed the whole matter on a firm foun- 

 dation by passing the bacteria through a long 

 series of artificial cultures and then by'inocular 

 tions, showing that they were capable of causing 

 the blight.*^' «' He further demonstrated that the 

 bacterial exudate from the tree, when freed of 

 bacteria by filtration, could not produce disease. 

 The results of an extensive study of the bacteria on 

 various media; of their morphology and stain 

 reactions were pubUshed by Arthur in 1886.«* Bacteria were 

 shown to penetrate twigs 3-4 dm. beyond their area of visible 

 effect.^"' 



In 1902 Jones ^ isolated an organism from blighted plum trees. 



Fia. 24.— Claw 

 from bee's foot 

 with blight 

 bacteria on 

 and about it 

 showingthe 

 relative size. 

 After Whet- 

 zei and Stew- 

 art. 



