OTHER BACTERIAL DISEASES OF PLANTS. 
305 
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. Be tee. 
Soft rot of onions is also caused by bacteria, and there are some 
other diseases less well known. 
The Tubercular or Tumor Diseases. The Olive Knot (B. 
savastanoi). This disease, first studied in 1886, and attributed 
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. Injhe 
peach it commonly produces an enlarged growth at the crown of 
26 
FIG. 54. The black knot 
of the olive. 
