PLUM DISEASES 369 



seem to warrant an account here. The disease is known in 

 Canada from Nova Scotia to Vancouver Island, and in Germany, 

 France, England, South Africa and New Zealand. It has been 

 the subject of observation and investigation since 1885, when it 

 was described in France. Outside of the United States, the 

 disease is said to be one of the most widely distributed of plant 

 diseases. While silver-leaf occurs chiefly on the apple in Canada, 

 it is primarily a plum trouble in other regions where it prevails. 

 The disease, known also as silver-blight and silver-disease, 

 affects, in addition to the plum and apple, many other fruit-trees 

 and bushes, as well as certain nut and forest trees. Among 

 these may be noted : peach, pear, cherry (wild and cultivated), 

 currant, gooseberry, almond, chestnut and ash. 



Of all the fruit-trees the plum is said to suffer most. Among 

 the plums it is quite probable that all varieties are equally sus- 

 ceptible to the spread of the pathogene, once the tree is infected. 

 It is a common notion, however, that soft-wooded varieties 

 are more commonly affected. In many instances this may be 

 explained on the grounds that such varieties are in the majority 

 in a given orchard or locality. On the other hand, if soft-wooded 

 varieties are more susceptible, the explanation may lie in the 

 fact that they are more susceptible to injuries, through which 

 the attack is made. Reports have it that the Victoria, Gibson, 

 Wales, Oullins, Early Rivers, Flemish, Czar, Monarch, Orleans, 

 Washington and Damson suffer more than other varieties. 

 Those said to be free from the disease in orchards where silver- 

 leaf occurs are: Diamond, Jefferson, Reine Claude, Den- 

 niston, Mirabelle, White Bullace, Sultan, Wales, Englebert and 

 Early Rivers. It will be perceived that certain varieties have 

 been observed by different individuals to be in one case sus- 

 ceptible, and in another, resistant. This is not surprising, 

 since so many factors must be taken into account in the con- 

 sideration of susceptibility and resistance of varieties to any 

 given disease. 

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