American Pomological Society. . 175 



occur. No doubt, there are other agents than those which I have ob- 

 served. I shall, however, confine myself to cases that seem well authenti- 

 cated by actual observation. I soon observed that a very large per cent 

 of the cankers on the limbs and upper part of the body occurred where 

 a sprout had been pruned away. For a long time I attributed this to 

 infection from the pruning knife, or from insects that followed the pruner 

 to suck up the exuding sap. That this was in some cases a correct de- 

 duction will appear later. The riddle was definitely solved for me early 

 in July. At this time twig blight became very prevalent. In the orchard 

 under observation, the Greening trees suffered severely from it. The 

 water sprouts which were now being put out abundantly were especially 

 subject to the attacks. Just how the disease is communicated to the twigs 

 and water-sprouts I am not prepared to say. I believe it is generally 

 .attributed to insects. Once in the watersprouts, however, the disease 

 progresses rapidly down the succulent tissues toward the limb from which 

 the sprout springs. If conditions are favorable and the sprout is not too 

 long, the bacteria reach the base and spread into the surrounding bark 

 tissue of the limb, giving rise to a typical limb canker. If the sprout arises 

 from the body, as is often the case in young trees, a similar result follows 

 and we have a typical body canker. The dead spur or sprout soon drops 

 away, and as its woody part rapidly decays for some distance into the 

 limb or body it is quite impossible after a time to tell just how the sprout 

 was removed. 



There were on the trees, along one side of the orchard, a large number 

 of cankers that could not be explained in the ways already described. 

 They formed collars of dead bark about the stubs of large limbs pruned 

 out the previous season. Instead of forming a callous and proceeding 

 to close the wound, the tissue had died often for a considerable distance 

 back from the cut surface and in some cases the canker had run down the 

 side of the adjoining limb. There were two trees on this side of the 

 orchard that were badly cankered, and from which dead and dying limbs 

 had been cut the previous season. I at once suspected the pruning knife 

 or the insects that followed after had been responsible for the infection.- 

 Proof of my theory came from an unexpected quarter. 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 water-sprout of several 

 years' growth. This I did with my knife, which I had but shortly before 

 used to cut from a fresh canker a piece of bark for inoculation purposes. 

 Some time after I observed a well developed canker about this pruned 

 stub. 



Of a similar nature to this are the cankers that arise from wounds 



