186 AMERICAN POMOLOGY. 



of the atmosphere may result in decay of the woody tis- 

 sues, or, if the sap exudes, at certain seasons, it may pro- 

 duce canker and fungous growths. In some varieties of 

 our cultivated fruits, wounds of this character are often 

 attended by an effusion of gummy matter ; this is particu- 

 larly the case with those that are known as stone-fruits, 

 and in these the excision of a large limb is seldom fol- 

 lowed by a deposit of woody matter in the way of healing 

 over the wound, which is always desirable ; hence in such 

 cases particularly, it is well to cover the exposed surface 

 with something to exclude atmospheric moisture, whether 

 this be paint, varnish of shellac, or common grafting wax. 



Insects, by eating the foliage extensively, very materi- 

 ally injure the healthy condition of a tree even the 

 minute aphides that suck the sap from the leaves and ten- 

 der bark, will seriously impair the health of our plants ; 

 but the borers that mine under the bark, extensively con- 

 suming the vital cambium, and even burrow into the solid 

 wood, reducing it to a honeycomb, cannot fail to affect 

 the healthy condition of the tree materially, and often 

 cause its premature death. Some knowledge of the habits 

 of these little creatures is considered of so great import- 

 ance, that the subject will be brought before the reader's 

 notice more at length in another part of this volume. 



There is no doubt, however, that many unhealthy con- 

 ditions of our trees, that might be traced to other causes, 

 but which are not manifestly dependent upon a want of 

 care on the part of the orchardist, nor upon a deficiency 

 in the constitution of the soil, are often attributable to the 

 inroads of these minute foes, which, in some cases at least, 

 are made the scape-goats upon which is laid the blame 



