248 



JOUKNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



occurs on trunks and limbs of apple trees, mostly older ones. 

 Swellings occur on the stems, and roots attempt to break throngh the 

 bark of them but dry up forming small warts upon the surface. This 

 is probably the most common form of " crown-gall " in this country. 



The galls are due to the presence of the bacterium Bacillus tume- 

 faciens (see Journal R.H.S. vol. xxxiv. p. 577). 



The results of numerous experiments are detailed and a large 

 number of observations on the behaviour of trees affected by crown- 

 gall are quoted. 



There appears to be some difference in the degree of susceptibility 

 in the different varieties and it was found that the disease was not 

 communicable to healthy uninjured seedlings but that wounded seedlings 

 were susceptible. The spread of the disease by the use of diseased 

 scions is very frequent, but after the first year the spread is practically 

 negligible and the pruning and grafting knives are not responsible for 

 much of it. 



The author believes the crown-gall organism to be so widely distri- 

 buted in the States that any system of eradication must fail, and as the 

 disease, according to the author, rarely does much harm, and does not 

 greatly spread, he advises leaving affected trees. He recommends that 

 wherever possible trees should be budded instead of root-grafted and it 

 may be that the comparative rarity of the root forms of the disease in 

 England is due to the practice of budding instead of root-grafting. 

 Root-grafting has found favour in the States as a means of checking the 

 ravages of woolly aphis. The use of ordinary calico for wrapping 

 grafts proved much better than anything else except rubber, and the 

 cost of the latter is prohibitive. It was more successful in keeping 

 out the germs of crown-gall than waxed cloth, waxed thread, and 

 so on. Other general notes upon careful cultivation are given 

 and the bulletin ends with a list of papers referring to crown-gall. 



F. J. C. 



Crown-Gall of Plants : its Cause and Remedy. By E. F. 



Smith, N. A. Brown, and C. 0. Townsend {U.S.A. Dep. Agr., Bur. 

 PI. Ind., Bull. 213; February 1911; illustrations). — The authors give 

 a history of our knowledge of the disease in various parts of the world 

 and of the discovery of the bacillus which is its cause {Bacterium 

 tumefaciens). Inoculation experiments were carried out since 1906, 

 and the results of these are here reported. 



A description of the bacillus, with its staining and cultural char- 

 acteristics, follows. The thermal death point is about 51° C, while the 

 optimum temperature for development lies between 25*^ and 28° 0. 



It has been found to attack (at least when purposely inoculated into 

 the plant) Compositae, Solanaceae, Oleaceae, Umbelliferae, Yitaceae, 

 Leguminosae, Rosaceae, Cruciferae, Caryophyllaceae, Chenopodi- 

 aceae, Urticaceae, Juglandaceae, and Salicaceae, and natural gnlls 

 have been studied on peach, apple, rose, quince, honeysuckle, Arbutus 

 Unedo, cotton, poplar, chestnut, alfalfa, grape, hop, beet, salsify, 



