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. 
2B 
