362 



Minnesota Plant Diseases. 



palisade fashion on the surface of the pocket. Each sac contains 

 about eight spores, which on germination may directly cause in- 

 fection of a host plant. The fungus of this disease is very closely 

 related to the peach leaf-curl fungus and to others forming 

 witches'-broom on birch, alder and cherry trees. It is a sac- 

 fungus with an arrangement of sacs similar to that in the true 

 cup fungi, but has no true cup, since the sacs occur directly on 

 the tissues of the host. 



FIG. 193. Plum pockets. These plums are devoid of stones and bear the fungus spores on 

 their surfaces. Photograph by H. Cuzner. 



The only known effective remedy for plum pockets is the 

 pruning back of the affected parts, so as to remove the fungus 

 mycelium. The pruning must in some cases be quite severe. Of 

 course all pockets must be removed and destroyed, as should all 

 affected parts. It is also advisable not to use the parts of any in- 

 fected tree for grafting purposes, since the fungus mycelium may 

 be transferred with the graft. It has been suggested that the 

 treatment w r hich is successful in combating the leaf-curl of peach 

 may also prove successful here. This consists in spraying with 

 bordeaux when the buds are swelling and again with bordeaux, 

 just before the petals fall. (See also Fig. 49.) 



