2o8 Bulletin 23G. 



cover) of the bacteria into healthy trees and Umbs also resulted in well 

 developed cankers. To these I have already referred (page 195 j. 



4. Production of twig blight with bacteria from canker (Figs. 67 

 and 69). — At the same time that the inoculations into the bodies of the 

 trees were made, bacteria from the same canker were introduced into 

 blossoms and tips of growing twigs of both pears and apples. These 

 were practically pure cultures, as a sterile needle was used to transfer 

 the bacteria from the canker to the twigs and blossoms. Infection took 

 place from nearly every inoculation, giving well developed cases of twig 

 and blossom blight in 10 to 14 days (Fig. 68). 



In the meantime, pure cultures were secured by dilution in agar plates 

 and also by direct transfer from the diseased tissue of the canker into 

 potato bouillon. A set of inoculations was now made from these pure 

 cultures into twigs and green fruits of both pears and apples. These like- 

 wise- resulted in nearly 100 per cent of infections. 



5. Observations on the formation of cankers. — During the early part of 

 July, twig blight became very common on the apple trees throughout the 

 region about Ithaca. There was also a second severe attack of it during 

 the latter part of the month and the early part of August. The blighting 

 of watersprouts and short shoots on the bodies and main limbs of the 

 trees resulted in the formation of many small cankers. Several of these 

 I carefully observed and photographed at different stages in their de- 

 velopment (Fig. 74). Pure cultures of the bacteria were also secured 

 from these sources. There was absolutely no doubt as to the nature of 

 the organism causing them. 



II. The Identity of the Canker Organism with that of the Fire 



Blight of Pears 



During the epidemics of twig blight just referred to, many of the 

 fruits of both pears and apples were observed to be affected with the 

 disease (Fig. 71). They showed on the surface watery spots which 

 gradually turned brownish, and during cloudy days drops of viscous exu- 

 dation appeared on the exterior. On cutting one of the fruits open the 

 flesh was found to be tough and leathery with a milky sap collecting at 

 the core. Gradually the flesh became brown and the fruit withered, finally 

 turning black, especially in the case of the pear, drying up and falling to 

 the ground. 



Pure cultures were now secured from the following sources: 



1. Active cankers on the limbs of apple trees (natural infection). 



2. Blitrhted twigs of apple (natural infection). 



3. Blighted twigs of pear (natural infection). 



