106 FRUIT BOOK. 



Plum trees are subject to a disease which has 

 been so destructive to them, as to have destroyed 

 nearly all the damson plums heretofore so com- 

 mon in our neighborhood. It appears at first a 

 greenish brown excrescence, which soon becomes 

 black. Various are the hypotheses which have 

 been given as to the cause of these warts. Some 

 have attributed it to the quality of the soil, others 

 to a redundance of nourishment, which distend 

 the cutaneous vessels by an extravasation of the 

 sap ; others, to the work of an insect. In our 

 examinations, &c. for years, we were not able to 

 find an insect in these excrescences while in a 

 green and fresh state ; and have heretofore been 

 inclined to adopt the theory of the distension of 

 the cutaneous vessels, considering the worms 

 which we have repeatedly found in these warts, 

 when black, to be a consequence and not a cause 

 of this disease. We have considered this ex- 

 crescence analogous to that which we find upon 

 the swamp pink, or azalea, called by boys swamp 

 apples, which has always been supposed by bo- 

 tanists to be caused by an insect. From farther 

 observation, we are inclined to believe that these 

 exudations are caused by a diseased state of the 

 sap. The only remedy that we have found effect- 

 ual has been the amputation of the diseased 

 limb. These excrescences always extending 

 themselves upwards, and not downwards, upon 

 the branches, would seem to prove that the dis- 

 ease either enters, in some manner, into the cir- 

 culation, or that the insect always ascends. 



We have not, as yet, found any variety that is 

 entirely exempt from this fatality ; but some ap- 

 pear to be more subject to it than others ; which 



