MAINE APPLE DISEASES. 375 



which has been reported as causing a great amount of damage 

 in apple orchards in other states, has not been found in Maine, 

 though careful search has been made for it. Almost none of 

 the characteristic twig blight or "fire blight" on the pear which 

 is a good indication of the presence of the organism has been 

 seen. If this disease occurs on the apple in this State, it is of 

 very rare occurrence. 



Crown Gall. Apple trees, particularly nursery stock, some- 

 times have galls or knots which are usually located near the 

 surface of the soil in the region of the collar. These galls are 

 often covered with many fine roots giving them a hairy appear- 

 ance. Such growths have been reported on a number of plants 

 which are closely related to the apple and also on other plants 

 which are not closely related. 



In the earlier studies of this disease the cause was not under- 

 stood. Injuries to the roots and unfavorable conditions of soil 

 and moisture were advanced as causes of the trouble. Experi- 

 ments were carried on in a number of places, however, which 

 demonstrated that the disease is communicable. In 1900, Tou- 

 mey* published an account of his studies of crown gall in which 

 he reports the results of extensive inoculation experiments. He 

 concludes that the disease is infectious and is caused by a slime 

 mold. The nature of this organism made impossible the use 

 of pure cultures in inoculations. 



More recently Smith** and Townsendt have studied crown 

 gall on a number of plants and they have been able to prove 

 quite conculsively that at least a part of the crown gall of the 

 apple is of bacterial origin, caused by the organism Pscndomonas 

 tumcfacicns Erw. Smith and Townsend. 



The organism was first isolated from galls on the Paris daisy 

 and inoculations showed that it could produce the disease. 

 Inoculations of tomato, tobacco, potato, sugar beet, grape, car- 

 nation, raspberry, peach and apple were also followed by the 

 development of galls. This led to the isolation of organisms 



* Tourney, J. W. Ariz. Exp. Sta. Bui. 2,?>- 1-64. 1900. 



*=>= Smith. Erwin F. and Townsend, C. O. A Plant Tumor of Bac- 

 terial Origin. Science, N. S. 25: 671-673. 1907. 



t Townsend, C. O. A Bacterial Gall of the Daisy and Its Relation 

 to Gall Formation in Other Plants. Science, N. S. (Abstract) 29: 273. 

 1 00 J. 



