368 MANUAL OF FRUIT DISEASES 
forming perennial cankers. Thus old neglected trees are par- 
ticularly a constant source of trouble and danger to other trees. 
These cankers are relatively large and deep on the Abundance 
and Burbank varieties. Cankers on the plum are somewhat 
e different in appear- 
ance from those on 
the apricot, necta- 
rine and_ peach. 
Open cankers are the 
more common type 
observed on the last 
three fruits, whereas 
on the plum the af- 
fected bark clings to 
the twig for some 
time. Watersprouts 
Fic. 107. — Black-spot on plums; developmental of plums may at 
si times show twenty 
or more cankers in various stages of development. 
See more complete account of Black-Spot under Peach, 
page 306. 
REFERENCES 
Jackson, H. S. Bacteriosis of plums. Delaware Agr. Exp. Sta. 
Ann. rept. 16-18 : 75-76. 1907. 
Lewis, I. M. A bacterial canker of plum twigs. American Micros. 
Soc. Trans. 31: 145-149. 1912. 
(Additional references to literature under Peach, page 311.) 
SILVER-LEAF 
Caused by Stereum purpureum Fries 
While this disease has not been observed with certainty on 
plums in the United States, it is known on apple, and its preva- 
lence and destructive nature in Canada and elsewhere would 
