126 MANUAL OF FRUIT DISEASES 
In America, its range and destructiveness have not reached 
proportions which even approach those in Europe. Yet in 
certain sections, already referred to, the canker is becoming 
troublesome; and it seems to be on the increase. 
So far as varietal susceptibility is concerned, little information 
is at hand for American conditions. But German authorities: 
say that growers have always spoken of cankerous varieties. 
It is held by some that thick-barked varieties are more resistant 
than others. Again, the matter of whether a variety is sus- 
ceptible or resistant is said to depend directly upon its suscepti- 
bility or resistance to frost-injury. Certain writers say that 
varieties of apples that grow erect and open, remain free from 
this canker, whereas others near by suffer severely. In con- 
tradiction to these observations and opinions, it is held that all 
varieties suffer alike, and that so-called resistant sorts, when 
planted among diseased trees, soon exhibit a susceptibility equal 
to that of their neighbors. Any variety, it is said, which is 
exposed is just as liable to infection as any other. It is admitted 
by some that weak-growing varieties show larger cankers, be- 
cause of their poor vigor, yet this is in most cases not worthy of 
practical notice. In Germany, susceptible varieties include the 
Canada Russet, Rheinischen Bohnapfels, Harbert’s Russet, 
Norman Bitter-Sweet, Gray French Russet, Hubbardston, 
Red Cardinal, Canada Reinette, Red Fall Calvill, White Winter 
Calvill, Winter Goldpearmain and others. Those resistant are: 
Fursten, Schaffelder, Boiken, Gravenstein, Carpentin, Eiser and 
Purple Red Cousinot. In England, Warner’s King is said to 
be notably less susceptible than other varieties. 
Symptoms. 
In later stages it is not at all difficult to detect the presence 
of the European apple-tree canker, nor to distinguish it from 
other kinds of cankers (Fig. 33). In the younger stages, how- 
ever, it is likely to be overlooked by the casual observer; and 
when noticed it is found to be not markedly different in appear- 
