PEAR BLIGHT 347 



organism. Efforts are being made to increase and extend 

 this natural immunity. Much more can be done in an ex- 

 perimental way in the breeding of resistant varieties of 

 plants than can be done with animals. 



Pear blight. The most important of the blights is that 

 which affects the pear and apple, and to a lesser extent the 

 quince, apricot, and plum, h was first observed in 1780 

 in the Hudson River valley, and as orcharding has spread 



Fior. 63. Pear Blight 



Normal fruit is shown on the ri^ht and diseased fruit on the left. In the 

 center one of tU- pears is healthy, the other is affected 



westward, the disease has developed, until it is now found in 

 all parts of this country and Canada. In Colorado it found 

 such favorable conditions that it has caused the abandon- 

 ment of commercial pear-growing. It has also caused great 

 losses in California. As far as our present knowledge goes, 

 the blight is of American origin and is confined to North 

 America. 



Thfc disease is readily recognized by the' fact that the 

 young twigs appear to have been injured by fire. This 

 condition has given rise to the common name of fire blight. 

 The loaves of the affected parts turn brown or black, and 



