Plate VI. An undescribed bark canker of apple. At left, typical canker on young 

 limb, checked bark in ])lace. In center, canker in which callus layers have met. 

 At left, old canker with decorticated bark; Pj'cnidia may be seen on low(>r j^ortion. 

 In center, the knob-like swellings produced by aphis are evident. 



