OTHER BACTERIA DISEASES OF PLANTS 329 
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 characteristic 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 pro- 
fusely than common, producing a swollen 
growth on the stem which is called the 
olive knot (Fig. 53). 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 Cali- 
fornia. 
The Crown Gall of the Peach and Other ns. 53 the ove. aot 
Planis (B. iumefaciens)—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 
the plant, between the stem and the root. The parasite that 
causes it has the power of growing upon a large series of plants, 
producing tumors in various parts of the plant which injure it 
more or less, according to the extent of the infection. Among the 
plants that may be infected with it are the raspberry (Fig. 54), 
the daisy, the hop, the radish, the cabbage, the tobacco, the sugar 
bect, the grape, the tomato, the oleander, the apple, and some 
others. It is unusual for a parasite to have such a long list of 
possible hosts, but in all these plants it has been demonstrated by 
Smith that tubercles will be produced by the inoculation of pure 
