Blight Canker of the Apple Tree. 



195 



is shown by the following incident : While making inoculations into the 

 body of an apple tree on the Station grounds, I had occasion to remove, 

 from near the base, a large sprout of several years' growth. This I did 

 with my knife which I had but shortly before used to cut bark from a 

 fresh canker. A typical canker soon developed about this pruned stub. 



(Fig. 17 •) 



Of a similar nature are infections that occur through wounds or 

 bruises on the limbs and bodies of trees. These wounds, commonly results 

 of " barking," may be made by careless workmen when plowing or work- 



FiG. 69. — Actively growing pear tivigs blighted by artificial inoculation with bacteria 



from ca]ikcr on limb of apple tree. 



ing about the trees or from the gnawing of animals; one of the worst 

 animals in New York is the woodchuck. A large percentage of such 

 wounds heal over eventually, but frequently through the agency of insects 

 or other means these wounds serve as infection courts for the canker 

 bacillus. An interesting case of wound infection came untler my observa- 

 tion last season. In cutting a cankered branch I accidentally "barked" 

 a healthy limb with the cut end of the diseased branch. The tree was 

 not again visited until some weeks later, when a large and actively spread- 

 ing canker was found to have developed about the abrasion (see front 

 cover). The bacteria were found in abundance in the diseased tissue and 

 pure cultures were secured. 



