BLIGHTS. 



497 



blight existed many years before this in eastern North America on some 

 of our native wild crabs, hawthorns, and wild plums, and with the intro- 

 duction of cultivated varieties, it found a new field for attack. As the 

 farming communities became more thickly populated, and the orchards 

 more numerous, it has spread gradually westward over the Allegheny 

 Mountains into the Mississippi Valley, across the Great Plains, and over 



FIG. 92. Two pear twigs. The upper one affected with Fire Blight, the lower one 

 healthy. (After Sackett, Mich. Agr. Exp. Sta.} 



the Rocky Mountains to the Pacific Coast. So generally is it distributed 

 over the United States and Canada that a blight-free orchard is, indeed, a 

 rare sight. The disease has progressed with such severity that, to-day, 

 commercial pear growing in Colorado has been practically abandoned, 

 and the industry in California is being threatened with destruction. So 

 far as our present knowledge goes, the blight is of American origin and is 

 confined to North America. 

 32 



