CROWN GALL 3 



shaped cell tissues. In its youngest stages the gall is a mass of soft 

 tissue with numerous minute areas of rapidly dividing cells scattered 

 throughout. These areas of sub dividing cells are centers of growth, 

 and as the galls become older these centers increase in size, and others 

 originate in the newly formed cell tissues. Ultimately, these centers 

 of growth become most curiously twisted nodules of woody fibers 

 and similar tissues. The following year, fresh parts of roots become 

 infected from the bacterial germs already in the diseased tissues. 

 It has been shown that the galls developing on the roots of a tree, 

 though separated by some little distance, may result from the 

 original infection. Mr. Erwin F. Smith, of the United States Depart- 

 ment of Agriculture, has called attention to the similarity ol growth 

 and development of crown gall in plants, and malignant tumors, 

 such as cancer, in animals. 



Injurious character. Crown gall, when occurring on the main 

 roots of plants, interferes with the movement of the cell sap and 

 thereby weakens the growth of the tree. This shortens the life and 

 the usefulness of the plant. The tap root and other roots which 

 are attacked are usually killed within a few years. Apple trees, 

 however, seem to be less injured than most other fruit trees. The 

 tissue of the gall decays in time, and this gives opportunity for 

 other parasites, including fire blight and root-rot, to develop 

 and further injure the growth of the tree. When an infected tree 

 dies in an orchard, and is replaced by a healthy one, the latter 

 very commonly develops crown gall, which is evidence that the 

 disease is easily transmitted through infected soil. More than this, 

 diseased trees in an orchard are a means of infecting other similar 

 healthy trees. 



Commoner plants which are attacked. Crown gall attacks practi- 

 cally all stone and pome fruit trees, including cherries, plums, peaches, 

 apricots, quinces, pears, apples, and nectarines, also almonds, wal- 

 nuts, chestnuts, grapes, blackberries, dewberries, raspberries, roses, 

 chrysanthemums, white poplars, willows, hops, and sugar beets. 

 On the grapes it is a very serious disease, one form of which is known 

 as black knot. As early as 1880 it appeared in California vineyards, 

 and later was brought to Arizona. Black knot may be recognized 

 easily on the grape by the large, irregular black knots or galls, 

 occurring at intervals on the vines. In different sections of our 

 country it is quite common on the blackberry and the raspberry, 

 occurring on the canes also. Occasionally it is found growing on 

 alfalfa, haps, and sugar beets, but, excepting upon hops, it is 

 not considered serious. However, such crops as these may be the 

 means of infecting orchard and nursery lands. Little variety 

 resistance has been found thus far among the different kinds f 

 fruit trees, though much work remains to be done in this direction. 

 Important inoculation experiments have been made regarding 

 the bacterium causing crown gall. The results seem to indicate 

 that all forms of crown gall are caused by the same bacterial 

 germ, though the galls often vary in size and shape on different 

 plants. Mr. Erwin F. Smith is of the opinion that the "hairy root" 



