Blight Canker of the Apple Tree. 



187 



" Crotch cankers " (Fig. 60) usually appear in the crotches where the 

 main limbs arise from the body, but may also appear in the secondary 

 crotches well up in the tree. In general characters they are similar to 

 the limb and body cankers. Owing to their peculiar position, water is 

 retained more readily in the dead bark, thus affording the very best con- 

 ditions for the entrance and growth 

 of rot fungi. These find easier ac- 

 cess to the heartwood at the crotch 

 than on the limbs. It was observed 

 that these crotch cankers heal much 

 less readily and successfully than do 

 the limb and body cankers. Crotch 

 cankers, unless promptly attended 

 to, mean the almost certain destruc- 

 tion of the trees. 



The large cankers at the bases of 

 young trees (Fig. 61), frequently 



referred to bv 



growers as 



collar 



Fig. 60. — Typical crolcli caiilccr. Dead 

 bark has been removed. Callus 

 forming about the margin. 



Fig. 59. — Large body canker result- 

 ing front successive seasonal at- 

 tacks of the disease. Originated 

 at the pruned stub. 



rot," are in many cases very prob- 

 ably due to the same cause as that 

 of the cankers on the upper parts of 

 the tree. The well known " collar 

 rot " of King trees may also be due 

 to the same or a similar organism. 



