410 



PLANTS AND MAN 



fatal, general inflammation of the abdominal lining known as 

 peritonitis. 



The spiral bacteria, or spirilla, are less important as disease 

 producers than either of the other two groups. However, some 

 diseases, notable among them cholera, result from spirillum in- 

 fections. The cholera spirilla destroy the red blood corpuscles, 

 in addition to producing extremely virulent toxins. 



Plant Disease 



Not so close to our personal welfare, but none the less of vital 

 importance, are the bacterial diseases of plants. First demon- 



FiG. 253. — Some bacterial diseases of plants include (A) crown gall and (B) 

 fire blight of pears and apples; G shows bacteria of fire blight in cells of the 

 flower. 



strated as plant pathogens only sixty years ago, bacteria today 

 are credited with causing many serious diseases of plants, out- 

 standing among these being the fire blight (fig. 253B) of pears, 

 apples, and quinces. This disease, in addition to occurring on 

 the hosts mentioned above, is found on many other cultivated 

 and wild plants of the Rose Family. It was probably native to 

 America but has spread to the Old World, outbreaks of the 

 disease having occurred in Italy and in New Zealand. Fire 

 blight is caused by a member of the bacillus type of bacteria, 



