158 



Bulletin 272. 



CgS) has proved that flies and wasps carry the bacteria from oozing 

 cankers to opening blossoms and from these to others, thus spreading 

 the Blossom Blight through the orchards. Our own observations tend 

 to show that the aphides and leaf hoppers are largely the responsible 

 agents in introducing the bacteria into the tips of growing shoots, while 

 the same insects and the curculio frequently introduce them into wounds 

 which they make in the fruit, thus giving rise to Fruit Blight (Fig. 14), 

 Man, himself, may be the unwitting or careless agent by which these 

 minute parasites find their way into cuts or wounds made when cutting 



Fig. 13. — Claw front bee's foot with Bliglii 

 bacteria on and about it to show the rela- 

 tive size. 



Fig. 14. — Blighted apple. 

 Bacteria introduced into 

 fruit by curculio. Note the 

 wound and oozing drops. 



out blighted limbs or in pruning the orchard (Fig. 15.) It has fre- 

 quently been demonstrated that the Blight bacteria may be carried 

 to the healthy trees on pruning tools. 



These bacteria pass the winter in some of the cankers in the bark 

 of the body or limbs of the tree (Fig. 6). The bacteria remain alive 

 only along the margin of the canker next to the healthy bark, and only 

 in those cankers that are more or less protected from drying out. These 

 few cankers in which the bacteria survive the winter are called " hold- 

 over " cankers. There is no way of distinguishing them from the cankers 

 in which the bacteria are all dead. There is some evidence that under 



'98 Waite, M. B. 



Life History and Characteristics of the Pear Blight Germ. 

 Proc. Amer. Assoc. Adv. Sci. 47:427. 



