CHAPTER XXIII 

 Bacterial Diseases of Plants 



THE microscopic one-celled plants called Bacteria or 

 Microbes are now known to be the cause of some of the 

 most destructive plant diseases. In a way the life history 

 of these bacteria is simpler than that of many of the fungi 

 affecting growing crops. The bacteria multiply chiefly by 

 a simple division of the cells, each single cell dividing into 

 two cells. This is a very rapid process, however, so that 

 when once within the tissues of a plant the disease-pro- 

 ducing microbes spread very quickly. Consequently, these 

 diseases are often called Blights. Another appropriate 

 name for some of them is Bacteriosis. 



PEAR BLIGHT 



One of the best-known and most characteristic of these 

 bacterial diseases is the Fire Blight of the Pear, Quince, 

 and Apple. The leaves on the branches affected by this 

 malady suddenly turn black as if injured by fire and hang 

 upon the twigs in this blighted condition for some time. 



This Blight affects pear trees much more than apple 

 trees and is the most serious obstacle in the way of suc- 

 cessful pear culture. It is very generally known simply 

 as the Pear Blight. It has been carefully studied by many 

 scientists, so that the characteristics of the disease are well 

 known. The microbe causing the malady was named 

 Bacillus amylovorns by Professor T. J. Burrill of Illinois. 



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