6i8 



"Crown-gall" in England. 



[NOV., 



passes on to its free surface, where numerous minute, globose, 

 yellow sporangia or fruit-bodies are formed. If a gall 

 containing the organism in an active, or swarming condition 

 is allowed to dry, the plasmodium concentrates into compact 

 masses, and passes into a resting condition. On the applica- 

 tion of moisture these resting masses of plasmodium 

 gradually expand and assume an active condition, moving 

 from cell to cell through the wall-pits, and consuming the 

 contents of the cells. " Crown-gall" is considered as a very 

 serious disease in the United States. Hundreds of thousands 

 of fruit trees have been killed by it when growing in the 

 best soil, and with the best treatment. The subject has 

 been very carefully worked out by Toumey, who describes 

 the galls as occurring on the following trees : peach, apricot, 

 almond, prune, plum, apple, pear, English walnut and grape, 

 cherry, poplar, chestnut, raspberry, and blackberry. 



Seedlings from one to six months old are most susceptible 

 to the disease. The galls appear in the region of the collar 

 or on the larger roots. A gall commences growth as a very 

 minute, smooth, colourless, wart-like body, often attached 

 to the stem or root by a narrow neck. Growth is rapid, and 

 the surface of the gall becomes nodulose or warted, and 

 darkens in colour. The galls usually decay at the end of 

 one season's growth, and leave an open wound which 

 extends for some distance into the wood. The following 

 spring gall formation commences round the margin of the 

 wound formed the previous season. These galls perish in 

 turn, and the process is repeated each season, resulting in 

 a large, deep wound. When two or three galls are produced 

 on different sides of the stem, it becomes so weakened that 

 the tree breaks off at the injured joint. 



Toumey has proved that the disease is of a contagious 

 nature. Healthy seedlings planted in soil mixed with sliced 

 galls contracted the disease, as did also healthy trees planted 

 in proximity to diseased ones. 



Since the investigations of Toumey were published, Messrs. 

 Erwin F. Smith and E. V. Townsend have devoted a con- 

 siderable amount of attention to the origin and cause of 

 "crown-gall," and have come to the conclusion that the primary 

 cause of these out-growths is a Bacterium, B. tumefaciens , , 



