327 



These areas he.siin as sliglit (liscoldratioiis, wliicli become deiu-essefl, ami a 

 distinct crevice marks the line between the healthy and diseased bark. 

 'I'he bark may fall, exposing the wood, or it may adhere closely to the 

 underlying wood. A plate of cork seems to limit for a time the extent 



Fig. 1. Twen;y Oun?e apple tree dying from the attacks of New York apple tree canker. Note 

 the characteristic dying out of the top. 



of the diseased area, but this is pierced and the healthy tissue invaded. 

 Soon the affected cells are killed ; they shrink, and the healthy portion 

 again is separated from the diseased by a crevice and by a second plate 

 of cork. This process continues until we have concentric rings as shown 



