OTHER BACTERIAL DISEASES OF PLANTS. 



305 



The Olive Knot (B. 

 in 1886, and attributed 



Soft rot of turnips, etc., produced by B. oleracea. 



Soft rot of carrots, produced by B. caratovorus. 



Soft rot of sugar beet, produced by B. tenthium. 



Soft rot of stored celery, caused by Pseud, fluorescens. 



Rot of iris, produced by Pseud, iridis. 



White rot of turnip, produced by Pseud, destructans. 



Gummosis of beet, produced by B. Beta. 



Soft rot of onions is also caused by bacteria, and there are some 

 other diseases less well known. 



The Tubercular or Tumor Diseases. 

 savastanoij. This disease, first studied 

 upon insufficient proof to a bacterial origin, 

 has recently been demonstrated to be a 

 bacterial disease. The bacillus is a motile 

 one with several flagella at one end and 

 grows in .ordinary culture media in the 

 laboratory. Several different bacteria have 

 been found associated with this disease, but 

 the one to which the above name has been 

 given is its cause, as shown by the fact 

 that the inoculation of olive trees with 

 cultures of the organism is invariably 

 followed by the appearance of the charac- 

 teristic symptoms of the disease at the point 

 inoculated. The effect of the bacillus is to 

 stimulate the plants to unusual growth. The various tissues of the 

 stem multiply more profusely than common, producing a swollen 

 growth on the stem which is called the olive knot (Fig. 54). This 

 injures the trees and sometimes kills them. The organism, so far 

 as known, enters- the plant exclusively through wounds. It occurs 

 in the various olive-raising countries of Europe and Africa, and also 

 in California. 



The Crown Gall of the Peach and Other Plants (B. tumifaciens.) 



This disease, until recently attributed to a different class of 



fungi, has now been proved to be caused by a bacterium. In^the 



peach it commonly produces an enlarged growth at the crown of 



26 



FIG. 54. The black knot 

 of the olive. 



