294 BUSH-FRUITS 



CROWN -GALL (Fig. 47) 



Woodworth, Bull. 99, Cal. Exp. Sta. Smith, Jour. Myc. 7:376. Bailey, 

 Bull. Cornell Univ. Exp. Sta. 74: 383; Bull. 117. Card, Bull. Nebr. Exp. 

 Sta. 39: 131. Selby, Bull. Ohio Exp. Sta. 79: 110; 92: 208; 104: 211. Hal- 

 sted, Kept. N. J. Exp. Sta. 1896: 413; 1898: 354. Tourney, Bull. 33, Ariz. 

 Exp. Sta. 



This disease is characterized by a rough, knotty growth about 

 the stem at the surface of the ground or on the roots beneath. 

 The knots or galls have a granular appearance, somewhat resem- 

 bling, when young, the callus growth at the end of a cutting. 

 When old, they look something like the black-knot of plums, but 

 are not so dark in color. In Germany the disease is known as 

 " Wurzelkropf ." On the Pacific slope it has ruined thousands of 

 trees, for its injury extends to fruit-trees as well as to brambles. 

 It has there been given the name Crown- Gall, which is probably 

 the best name to retain, though the trouble is not confined to the 

 crown of the plant. Although a widespread disease, its cause has 

 been discovered but recently. The trouble has often been attrib- 

 uted to the work of the gall-fly, Ehodites radicum, but the galls 

 made by that insect are very different. Nematodes, or eelworms, 

 have been so frequently associated with the galls that some have 

 been led to think them the cause of the trouble. 



Professor Tourney carried on an extended and careful series of 

 studies at the Arizona Experiment Station which led him to the 

 belief that the disease is due to the presence of a specific organ- 

 ism belonging to the slime-molds or Myxomycetes. Although 

 many species of slime-molds are known in America, but one has 

 heretofore been known to be parasitic, and that one was doubt- 

 fully placed in the group. As a class, the slime-molds belong to 

 a very low order of plant-life and exist chiefly on decaying vege- 

 table matter. The one responsible for the crown-gall is so unlike 

 the others that Professor Tourney thinks it should be placed in an 

 entirely new genus from any yet described. He, therefore, erects 

 a new genus and species, giving the organism the name of Dendro- 

 phagus globosus. 



Professor Tourney's experiments prove, as have experiments 

 made by others, that the disease is readily transmitted from one 

 plant to another. When minced galls were mixed with the soil in 



