THE SPRUCE INVESTIGATION. 



245 



As is well known, the newly forming or growing tissue and 

 liquids, between the inner bark and outer wood, the cambium, 

 is the most vital part of the iving tree. Therefore, it is plain 

 that any injury like that resulting from insects mining beneath 

 the bark, must result in an abnormal condition, weakened vi- 

 tality or death of the parts so infested, and that if the attack is 

 sufficient on certain 

 parts of the tree to 

 overcome the natural 

 resistance and efforts 

 of the injured tree to 

 heal the wounds, the 

 weakened vitality of 

 the entire tree must 

 follow. When this 

 occurs, its recovery is 

 prevented by numer- 

 ous other bark and 

 wood infesting in- 

 sects, which on this 

 account, are attracted 

 to it. Thus, we find 

 that the insect which 

 is capable of mining beneath the healthy bark of a living cree, 

 is the one to be especially dreaded, since it mnst be the leader 

 in the attack and must overcome a certain decree of the re- 

 sisting forces, before its numerous allies or dependents can 

 render assistance in the destruction of a single tree or a forest. 



THE DESTRUCTIVE PINK BARK BEETLE. 1 



Strange as it may seem, this is the only one of the many species 

 of bark borers observed in the spruce that was found making 

 a primary attack on the healthy bark of living trees in such a 

 manner as to cause their death. Therefore, it is leyond a doubt, 

 entitled to highest rank among the insect enemies of the spruce, 

 as well as the pine. The hundreds of dying and dead, as well 



Fig. XXII. -Nuptial chambers of Tomicus pint in 

 black spruce. 



Dendroctonusfrontalis, Zimm. 



