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THE CROWN GALL OF FRUIT TREES. 



By W. Lochhead, Macdonald College. 



The Crown Gall has been for many years a widespread disease of 

 apple, peach and other members of the Rosaceae. As the name suggests, 

 the enlargements or galls occur mainly at the crown of the root ; but they 

 may occur either above or below the surface, and on the smaller roots. At 

 :first they are small and almost translucent but their growth is rapid, and 

 later in the season they become brown and often spongy. On account of 

 their occurrence at the crown some investigators believe that the galls are 

 the result of the irritation caused by injuries produced in transplanting, 

 by rodents, or by implements of cultivation. However, the infectious 

 nature of the disease would suggest another cause. Many experiments 

 have been carried out to prove this point. Hedgcock performed many in- 

 oculations of roots of rosaceous trees and shrubs with macerated galls, 

 which showed clearly that seedlings of almond, peach, raspberry and 

 •others could be inoculated in this way, although there was a wide range of 

 degree of susceptibility, even in different varieties of the same plant. 

 Moreover, healthy roots became diseased when infected parts of diseased 

 plants were buried near them. 



The galls appear to possess an ''annual structure, beginning their 

 growth with exfoliation in the spring and maturing more or less by the 

 time of leaf fall. As a rule, the mature disintegrated galls do not develop 

 secondary galls from any portion of the old wood. Young galls may, how- 

 ever, spring from the collar or roots near the margin of the gall pre- 

 viously formed, and thus the wounds and injurious effects are intensified 

 from year to year." — (Duggar). 



Tourney, who first made an investigation of Crown Gall, thought the 

 disease was caused by a slime-fungus which he named Dendrophagus 

 globosus, as he found that a slime- fungus developed frequently on the 

 cut surfaces of galls and the appearance of the protoplasm in certain 

 cells of the gall suggested stages in the development of the plasmodia. 



Lately, however, Messrs. Erwin Smith and Townsend of the Bureau of 

 Plant Industry, AVashington, have produced good evidence of the bacter- 

 ial origin of the disease. An investigation was made of the galls on the 

 roots of Paris Daisy (Chrysanthemum frutescens) and a pathogenic bac- 

 terial organism was isolated, with which they were able to inoculate seed- 

 lings of many plants, including raspberry, peach and apple. To this 

 organism was given the name of Pseudomonas tumefaciens. 



