Blight Canker of the Apple Tree. 209 



4. Blighted fruit of pear (natural infection). 



5. Blighted fruit of apple (natural infection). 

 (Two cultures from widely separated local- 

 ities.) 



6. Blighted fruit of apple (artificially infected 

 from canker on apple limb). 



The pure ctiltures of bacteria from these dif- 

 ferent sources were each carried through 12 

 differentiating kinds of media (see page 210) 

 and a careftd record of growth, characters and 



reactions made. The comparative study ^^^- ^4- Bacteria directly 



^ . -^ jrom active canker on 



showed the growth on a given medium to be appJe tree. Stained in 



the same for all the different cultures, thus carbol fuchsin. Showing 



various forms oj the or- 

 establishing beyond a doubt the identity of the ganism as they occur in 

 organisms causing the canker on the bodies ^^'^ diseased bark. 

 and limbs of apple and pear trees and the fire- and twig-blight of these trees. 

 A third set of inoculations was made with the bacteria from certain 

 of the above cultures. This was in August and the young shoots of the 

 pear had ceased to grow. The fruits, however, were in just the right 

 stage for infection. The shoots of the apple were still actively growing. 

 Some 10-12 cross inoculations each were made as follows with the 

 bacteria : 



1. From canker to twigs of apples. 



2. From canker to fruit of pears. 



3. From twigs of pears to twigs of apples. 

 All gave nearly 100 per cent of infections. 



12. Notes on the Morphology and Cultural Characters of the 

 Organism, Bacillus amylororus (Bur.) DeToni 



Morphology. — Direct from an active apple tree canker in hanging 

 drop of sterile tap water. Short rods with rounded ends, single in- 

 dividuals nearly oval, 1.5-2 long, a little more than half as thick, oc- 

 curring singly, in pairs, fours or even more, end to end. Many but not all 

 motile. 



The organism was also examined (in hanging drop of beef bouillon) 

 from cultures on the following media: Beef bouillon, agar plate, agar 

 slant, milk and potato plugs. All of these cultures were two days old 

 except the agar plate and milk, which were several days older. The milk 

 had thickened. The organisms varied little in these different media from 

 the form and size observed in those direct from the diseased bark. They 

 occurred singly or in pairs and frequently in short threads except on the 

 potato plugs. There they were nearly all single. They were motile in 

 all of the media examined but exceedingly so on potato plugs where they 

 also appeared to be slightly larger. 



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