THE PLUM WART. 495 



III. Diseases affecting the Stem. 1. The Plum 

 Wart — Sphaeria ?7iorbosa. This is a fungus com- 

 mon in the United States, where it attacks particu- 

 larly, but not exclusively, the plum. It sometimes 

 appears on the cherry. It produces great, gouty 

 swellings upon the branches, and the glands of 

 the bark look as if they had received poison. This 

 is its appearance in the autumn. In the spring the 

 part is very much enlarged, the skin broken, and 

 the soft substance exposed, leaving the wound raw. 

 It soon changes from its natural yellowish-green, 

 color to black ; and the fungus then becomes quite 

 visible. The curculio takes advantage of this soft 

 place to deposit its eggs. It is doubtful whether 

 there is any remedy for the disease ; but it can be 

 checked by vigorous amputation. 



By some this wart has been attributed to the 

 sting of the curculio, because its larvae are so often 

 present. But this is not always the case ; and the 

 disease is often very prevalent where the curculio 

 is not very abundant, and where it could find many 

 other more natural and desirable positions in which 

 to deposit its eggs. 



By others it has been attributed to rankness of 

 growth, or the absorption of some poisonous ma- 

 terial. Another writer thinks it is the result of 

 the extremes of temperature which take place during 

 the period of growth. He says that his opinion is 

 corroborated by the fact, that years ago, before the 



