DISEASES OF THE PLUM 293 



The symptoms of gummosis is the accumulation of a 

 gummy exudation on the trunk and the branches of the tree. 

 The gum at first is light colored and soft, but later turns 

 a dark yellowish color and becomes hard. This gummy 

 material accumulates in large quantities at certain points, 

 particularly in crotches and places where a limb has been 

 split. Small patches are usually found scattered over the 

 trees at many points. 



FIG. 120. Black knot of the plum. (New Jersey Agriculture Experiment 



Station.) 



The cause of this trouble is due to a number of things and 

 in reality is only an attempt by nature to protect a wound on 

 the plant. Borers, insect injuries, splits or any injury to the 

 tree will often cause the plum to exude this gummy material. 

 Usually no great injury results from its presence, and the best 

 way to get rid of it is to remove the primary cause, whatever 

 that may be. 



