196 



Bulletin 236. 



Fig. 70. — Half grown apple 

 inoculated willi pure cnl- 

 ttirc of bacteria from can- 

 ker on liiub of apple tree. 

 Noic inilky drops exuding 

 from diseased tissue. 



The wounds or punctures of insects seem 

 to be directly responsible for some of the in- 

 fections. Sometimes cankers on the bodies 

 of trees cannot be attributed to infection 

 through blighted shoots. In some cases 

 these cankers have been traced directly to 

 the wounds made by insects. Fig. 78 shows 

 a hole made by a borer at the base of a tree 

 and surrounding it is a well developed 

 canker. It is very probable that many of 

 the cankers at the base of young trees origi- 

 nate in wounds made by borers. The bac- 

 teria are probably carried to these wounds 

 by flies or other insects which visit these 

 places to feed on the exuding sap and excre- 

 ment. The infecting agents in the case of 

 crotch cankers have mot as yet been defi- 

 nitely determined. It seems likely that in- 

 sects again are here responsible. I have 



Fig. 71. — Naturally infected apple. Infection probably took place 

 in the spur at the base of the stem, through which it worked its 

 way to the young fruit. 



