DESTRUCTION OF SPRUCE FORESTS. 815 



for what purpose is uncertain. In one instance the two beetles were found at work 

 making these perforations, boring through from the inner surface of the bark. In one 

 instance the third was less than half an inch above the second, so that there would 

 seem to be no particular necessity for it. 



The eggs of the insect are deposited along both sides of the upper part of the fur- 

 row. They lie close together, almost or quite in contact with each other. When the 

 larvfB emerge from the eggs they begin to feed upon the soft cambium and to work 

 their way under the bark at right angles to the main furrow. They are at first so 

 minute and work so close together that they make no distinct furrows, but seem rather 

 to devour entirely a very thin layerof the cambium ; bat as they increase in size they 

 begin gradually to form distinct furrows and to take directions more divergent from 

 each other, and from their original course. In this way colonies from contiguous fur- 

 rows at length run together, and in time the whole is surrounded by their multitu- 

 dinous pathways, and the death of the tree is accomplished. Great care is taken by 

 the parent beetles to keep their furrows separate. No instance was observed in 

 which they ran together. In one instance the course of a furrow was changed to 

 avoid running into the lateral furrows of a colony of larva) just above. No furrows 

 were found in the tree more than 10 or 12 feet from its base, thus indicating that the 

 attacks are made upon the lower part of the trunk. The attacks are not made simul- 

 taneously. Some of the furrows in this tree were scarcely more than an inch long, and, 

 evidently had been just commenced. Others were fully excavated and contained eggs, 

 and in others still the larvae had hatched and commenced their work, but in none were 

 they fully grown. In another tree, a few rods distant from the first, the attack had 

 evidently been made earlier in the season, for the larvse were further advanced in size 

 and the bark on one side of the tree was well loosened, though, strange to say, the 

 other side of the trunk was comparatively unharmed. I was unable to discover why, 

 in this instance, the attack was limited to one side of the trunk. It is pretty evident, 

 therefore, that the trees are attacked all along during the months of June and July, 

 and possibly as late as August. I suspect, also, that the parent beetle, after having 

 established a colony in one place, may emerge from her furrow to repeat the opera- 

 tion in another place, either in the same trunk or in a different one, but this I was 

 not able to ascertain definitely. 



A whitish fungus, Polyporus volvatus Pk., scarcely larger than a hickory nut, occurs 

 in considerable abundance on the trunks of spruces killed by this beetle. The myce- 

 lium of the fungus grows beneath the bark, and the external plant is connected with 

 it through the perforations made by the insect. Hence this fungus becomes a con- 

 spicuous indicator of the track of the beetle and tells the tale of its destructive power. 



Ill a subsequent report, the thirty-first, Mr. Peck thus refers to the 

 injuries by Dark-borers of the balsam fir: 



The wood of the balsam is of little value for lumber, owing to the small size of the 

 tree. It contains resin and burns freely, but with a crackling noise. The smoke is 

 very penetrating and irritating to the eyes. Near the summits of the mountains, how- 

 ever, it is almost the only available wood for camps and camp-fires. The bark of this 

 tree furnishes the well-known " Canada balsam," a clear viscid resin of considerable 

 repute in medicine and much used in mounting objects for the microscope. The resin 

 is obtained from small vesicles or " blisters" in the bark. 



It is generally more abundant in the thrifty, smooth-bai*ked trees of low damp 

 lands, than in the stunted growths of the mountains. Because of the value of this 

 tree as a producer of balsam, and because of its beauty and fitness to adorn parks and 

 pleasure grounds, it ought to be cherished and preserved. But like its companion, 

 the spruce, it has its insect and fungoid foes. While at Summit, in Schoharie County, 

 in September, I noticed in a small grove of balsams that a dozen or more of the trees 

 had recently been killed or were then dying. The leaves had nearly all changed their 

 color, but for the most part yet remained on the trees. 



