XIII. THE OLIVE TUBERCLE 



(Syn. Olive knot) 



Type. This disease is a conspicuous overgrowth. It occurs 

 on wild and cultivated olives, forming large or small, irregular, 

 spongy or cheesy knots or excrescences (Figs. 297, 298) which 

 decay rather quickly. Attacked limbs are dwarfed or killed, 

 and occasionally the whole plant is destroyed, particularly if small 

 and on irrigated land, but more often the trees are only stunted 

 and rendered unfruitful. New outgrowths often occur around 

 the old dead knots, and also similar growths at a distance from 

 them. Roots, trunk, branches, and leaves, are subject. Often 

 when a terminal shoot is attacked it ceases to grow, even if 

 it had been very vigorous (Figs. 299, 300), and the branch 

 is continued by one or more of the lower side shoots, the terminal 

 shoot dying. Once attacked a tree seldom or never recovers, 

 that is, the disease persists from year to year, and invades new 

 shoots and lower parts of the old (Fig. 301). 



No tumor-strand occurs and the secondary tumors have the 

 structure of the tissue in which they are lodged, i.e., the disease 

 is a granuloma. The bacteria are abundant and easily visible, 

 being lodged first between the cells and eventually in intercellu- 

 lar, irregularly branched cavities, around which the tissue often 

 has a water-soaked or brownish appearance (Figs. 302, 303). 

 During rainy weather the bacteria ooze readily to the surface 

 of the tumor in great numbers (Horne) whence they are washed 

 to .other parts of the same tree and carried probably to other 

 trees, entering through wounds to form other tumors. Deep 

 tumors may also arise at a distance from the first tumor and 

 these are due to bacteria which have migrated from the primary 

 tumor by way of the spiral vessels of the inner wood which in 

 such cases are browned, more or less disorganized, and occupied 

 by the gray-white slime of the bacteria (Figs. 304 X, 305). The 

 knot contains or may contain both wood and bark, the vessels, 



389 



