REPORT ON FORESTS. 221 



or sap-wood at all, it is for a short time only in the early stages 

 of growth. The tree derives its chief supply of nourishment 

 through this bast and sap-wood, which is scarcely at all injured 

 by these larvae, hence they may work for many years without 

 causing fatal results, if they are alone in their attacks. The 

 Scolytid borers working the sap-wood or bast interfere at once 

 with the nourishment of -the tree, and the results are immedi- 

 ately noticeable. The result of this difference from a practical 

 standpoint is that a tree killed by Scolytids may make fair tim- 

 ber ; one that has been long infested by longicorn borers will be 

 worth little or nothing, though the insects may not have killed 

 the tree. The function of other of these borers attacking dead 

 or dying wood will be again referred to. 



Flat-headed borers resemble the round-headed forms in general 

 shape, but are compressed and flattened, the " head " segments 

 comparatively broader and the body somewhat longer, so that 

 they have been called "hammer heads." These borers in the 

 main attack weak, sickly or dead trees, though one group, the 

 Agrilids, forms an important exception. They live chiefly just 

 under the bark or in the sap-wood, forming irregular shallow 

 chambers connected by short, irregular galleries. Some of them 

 live two or three years in the larval stage, and, before trans- 

 forming, bore a short distance into the wood to form a pupal 

 chamber, issuing later through a hole in the bark, as do the 

 longicorns. It is easy to determine at all times whether a tree 

 has been infested by round or flat-headed borers, for in the first 

 instance the exit hole is as round as if it had been bored by an 

 auger, while in the latter it is regularly oval. The flat-headed 

 borers come with or after the Scolytids, rarely before, and when 

 the two are together present the flat-headed grubs often extend 

 their chambers throughout an entire .gallery system of a bark 

 beetle, destroying everything in their way. 



The adults of these borers are Buprestids, for whom there is 

 no satisfactory common name. They are long and narrow, some- 

 what flattened, tapering posteriorly, very hard in texture and 

 generally metallic in color. Some of them are bright green, or 

 brilliantly copper gilt, but most of them are more soberly bronzed 

 or have a metallic green or blue reflection. 



The species of Agrilus are the smallest of the series, rarely 

 more than one-quarter of an inch long, very slender and always 



