170 LUTHER BURBANK 



oriental pear, it must be understood that the 

 blight is a malady of such virulent nature that 

 when it attacks the pear tree it very commonly 

 results in killing it outright. This suggests, 

 obviously, a peculiar susceptibility on the part of 

 the pear. Such susceptibility is manifested, un- 

 fortunately, in exceptional measure by the best 

 European varieties, including the Flemish 

 Beauty and the Bartlett. This, presumably, is 

 the penalty of overspecialization in a certain 

 direction, or unbalanced selection. 



Until very recently the cause of pear blight 

 was much disputed, but conclusive proof is now 

 furnished that it is a bacterial disease, due to the 

 presence of a germ that has been named Bacillus 

 amylovorus. 



This germ has close cousinship with the vari- 

 ous tribes of bacilli that cause the contagious 

 human maladies. And there is a curious resem- 

 blance between the assault of the microbes on the 

 pear tree and the corresponding assaults of cer- 

 tain bacilli, for example the diphtheria bacillus, 

 on the human organism. In one case as in the 

 other, the bacilli, once they find a lodging place, 

 multiply inordinately and give out excretions 

 that are virulently poisonous. Located on the 

 flowers and fruit of the pear, or finding their 

 way to the inner bark or cambium layer of the 



