170 TREE WOUNDS AND DISEASES 



the south and west. In the case of both 

 orchard and forest trees the term " canker " is, 

 however, very loosely applied whenever the 

 bark and wood are in a diseased condition, 

 though in the present case it is understood to 

 refer directly to attacks of the above-named 

 fungus. Amongst fruit trees, the apple is most 

 liable to the attacks of canker, though both 

 the pear and plum are by no means exempt, 

 and certain kinds of each are far more suscep- 

 tible than others to the ravages of this fungus 

 pest. The first appearance of the disease is 

 not very marked, in which the bark looks 

 as if gnawed or eaten away, thus exposing the 

 wood to view. Gradually the bark around the 

 wound splits into fissures, becomes thick and 

 rugged, and assumes a withered brown appear- 

 ance. Young and tender wood naturally suffers 

 most, and in this case the spread of the disease 

 is rapid and persistent, the bark gradually fall- 

 ing off in flakes, and finally resulting in the 

 death of the branch. As the canker fungus 

 is a wound parasite, it can only gain a footing 

 through injuries to the bark, such as would be 

 brought about by insect attacks, the browsing 



