70 INSECTS INJURIOUS TO VEGETATION. 



lumps, with a cracked, uneven, granulated surface. The wood, 

 besides being deprived of its nutriment, is very much com- 

 pressed, and the branch above the tumor perishes." Dr. Burnet 

 rejected the idea of the insect origin of this disease, which he 

 considered as a kind of fungus, arising in the alburnum, from 

 an obstruction of the vessels, and bursting through the bark, 

 which became involved in the disease. These tumors appear 

 to me to begin between the bark and wood. They are at first 

 soft, cellular, and full of sap, but finally become hard and 

 woody. But whether caused by vitiated sap, as Dr. Burnet 

 supposed, or by the irritating punctures of insects, which is the 

 prevailing opinion, or whatever be their origin and seat, they 

 form an appropriate bed for the growth of numerous little 

 parasitical plants or fimg-i, to which botanists give the name 

 of Sphmria morbosa. These plants are the minute black gran- 

 ules that cover the surface of the wart, and give to it its black 

 color. When fully matured, they are filled with a gelatinous 

 fluid, and have a little pit or depression on their summit. 

 They come to their growth, discharge their volatile seed, and 

 die in the course of a single summer ; and with them perishes 

 the tumor whence they sprung. It is worthy of remark that 

 they are sure to appear on these warts in due time, and that 

 they are never found on any other part of the tree. 



Insects are often found in the warts of the plum-tree, as 

 well as in those of the cherry-tree. The larvae of a minute 

 Ci/nips, or gall-fly, is said to inhabit them,f but have never 

 fallen under my observation. The naked caterpillars of a 

 minute moth are very common in the warts of the plum-tree, 

 in which also are sometimes found other insects, among them 

 little grubs from which genuine plum-weevils have been raised. 

 This is a very interesting fact in the economy of the plum- 

 weevil. It may be questioned, however, whether it be a mere 

 mistake of instinct that leads the curculio to lay its eggs in 

 the warts of the plum-tree, or a special provision of a wise 

 Providence to secure thereby a succession of the species in 

 unfruitful seasons. 



t Schweinitz, Synopsis Fungorum ; in Trcinsactions of the American Philo- 

 sophical Society, Philadelphia. New Series, Vol. IV. p. 204. 



