These citations are enough to show that the disease is of special 

 economic importance and greatly dreaded by many fruit growers. 



Symptoms. The first indication of fire blight is seen either in 

 the browning and subsequent blackening of the leaves or of the 

 young twigs or of the tender shoots. When the twigs or shoots are 

 the principal parts affected the disease is spoken of as twig blight. 

 Pears show the presence of the disease more frequently by the 

 blighting and blackening of the leafy tufts of the spurs, and show it 

 especially by the darkening of the blossom clusters on the larger 

 clusters, while, later, the branches themselves become blackened 

 The progress of the disease is always downward — an inch or more 

 each day, depending upon the season, until the larger branches are 

 infected. In the more susceptible varieties it spreads more quickly, 

 involvino- the whole tree; but in the more resistant varieties the 

 progress of the disease is not so fast. When the disease is active 

 the bark of the diseased branches cracks, and a thick, blackish, gummy 

 fluid exudes, and later the infected bark becomes hardened, dry and 

 shrunken. The disease occasionally appears on the larger branches 

 and trunks of fruit trees when these have been bruised or otherwise 

 injured, when its appearance is similiar to the injury known as "sun- 

 burn " or " sun -scald." This disease of the trunks or larger branches is 

 sometimes spoken of as "body blight" or "rough bark." The inner 

 bark and cambium layer of the limbs and trunk are the most 

 important parts of the tree killed by the blight. Instances are known 

 of its attacking the fruit, producing watery ulcers accompanied by 

 brown discoloration and decay. The disease may be known by its 

 peculiar odor, said by some writers to resemble putrefaction. 



When the disease is in progress, the discolored blighted portion, 

 blends gradually into the color of the normal bark, but when th& 

 disease has stopped there is a sharp line of demarcation between the 

 diseased and healthy portions. (Waite). 



Microscopic Appearance of the Diseased Tissues. The most con- 

 spicuous change in the tissues affected with the blight is the dis- 

 appearance of the stored starch, and on account of this peculiarity 

 the organism has been named the " starch destroying bacillus " 

 (Bacterium amylovorum). The germ penetrates from one cell to 

 another and produces a gummy or mucilaginous matter which is 

 found on the exterior of the affected parts. The microbe is found, as 

 a rule, only in the inner bark and the actively growing tissues 

 (called the cambium, which produces wood on the inner side and bark 



