124 MASSACHUSETTS HORTICULTURAL SOCIETY. 



and in some cases involving the entire tree and killing it. It is this 

 destructive form of the disease that has earned the name "fire 

 blight." 



There is another form of the disease quite commonly overlooked 

 or not understood by the grower. I refer to the cankers formed on 

 the body and main limbs of the trees and known as "blight cankers " 

 or "body blight." These cankers are for two reasons perhaps the 

 most dangerous form of the disease. First, because they may of 

 themselves kill a limb by girdling it or what is more often the case 

 not kill it directly but serve as infection courts or avenues for the 

 entrance of rot-producing fungi that soon destroy the tree by rotting 

 the wood; and, second, because as I shall explain more fully later, 

 they serve to carry the bacteria over from one season to the next. 

 There are several kinds of cankers that occur on apple and pear 

 trees. A canker may be defined as a dead spot or area in the bark 

 of the tree. It may be rough and swollen or smooth and sunken. 

 Blight cankers are always when first formed smooth and slightly 

 sunken and sharply defined by a distinct crack between diseased 

 and healthy bark. They commonly occur on the main limbs and 

 branches of the tree. Young apple trees just coming into bearing 

 are more commonly affected with this form of the blight than are 

 older ones. Blight cankers vary in size from spots no larger than 

 a dime to areas a foot or more in length and sometimes encircling 

 large limbs. On the main limbs and upper part of the body small 

 cankers are frequently formed. These I have called "pit cankers" 

 from the fact that the healing callus soon forces out the dry dead 

 bark of the diseased spot leaving a depression or pit, extending 

 into the wood. Such cankers are dangerous only in that they 

 serve as a point of entrance for rot fungi. Sometimes the bacteria 

 get into the crotch of the main or secondary branches forming 

 "crotch cankers." 



These cankers just described are seldom the result of the direct 

 introduction of the bacteria into the bark by some infecting agent. 

 The chief avenues of entrance of the bacteria into the body of the 

 tree are I believe through blighted spurs and water sprouts. An 

 examination of a number of these cankers during the time when 

 they are being formed will shoAv at the center of almost all of them 

 a blighted spur or shoot. The bacteria may also be introduced 



