360 



BACTERIAL DISEASES OF PLANTS 



early autumn, the blight ceases to spread, and the organism, in 

 a majority of cases, dies out of the blighted (killed) trunk and 

 limbs, but in a variable per cent of cases the bacteria persist in 

 certain patches, forming what Mr. Waite, who discovered it, 

 has termed "hold-over blight," and Prof. Whetzel " cankers." 

 From these spots (Figs. 282 and 283), which ooze living and 





FIG. 276. Fire-blight on a pear tree. Healthy and blighted branches, seen close. 



Maryland, July 1, 1914. 



virulent bacteria, especially during the increased sap-flow of the 

 spring, and which are visited by bees and other pollen-gathering 

 and nectar-sipping insects, the exudate being sweetish, accord- 

 ing to O'Gara, the bacteria are carried to the blossoms of neigh- 

 boring trees and a new outbreak is started, the organism, brought 

 by these insects, growing first in the nectar of the flowers or in 



