EEMEDIES AGAINST FOREST INSECTS. 27 



less sharply distiuguisbed ; and it is only in the oaks, ashes, and elms, 

 where the pores are arranged in rings ("ringporen") that the ricbly 

 vascular spring wood sharply defines each new annual ring from the 

 denser and more compact autumnal layer of the preceding ring. 



Injuries in the production of the resin also arise from molds, which 

 effect a transformation of the starch and of the cellulose into turpen- 

 tine, and thus cause a morbid increase as well as outflow of the resin or 

 pitch ; e. g., Agaricus melleus, Aecicliumpini, Peziza Willkommii. All in- 

 sects which externally gnaw the bark or the wood of coniferous trees, e. </., 

 bark borers, wood wasps, Grapholitha pactolana and G. coniferana, Dioryc- 

 tria abietella; different weevils (Hylobius aud Pissodes), produce a more 

 or less strong flow of pitch or resin. But also in the interior of tbe wood 

 arise abnormal formations, as, for example, the so-called pitch-chains. 

 We understand by these a morbid increase of the pitch canals of coni- 

 fers into concentric chains which often coalesce ; also the pitch canals 

 in the last year's ring are completely omitted. 



Prevention and remedies against forest insects. — Besides the insecticides 

 for such insects as feed upon the leaves, and the means of applying 

 them to single trees, to groves, or to more or less extensive forest areas, 

 and which will be described farther on by Professor Riley, there are some 

 suggestions which may be made as to the remedies against borers. 



In the first place it should be borne in mind that dead stumps and 

 decaying trees or logs left standing near groves or road-side trees, are 

 a continual menace to healthy trees, since they afford an asylum or 

 breeding-place to timber and bark borers. Such objects, large and 

 small, should be cut down or pulled up and burnt. Forests should be 

 kept free from standing dead trees and stumps, or if left standing 

 should have the bark removed. It is well known that lumberers remove 

 the bark of logs to prevent injury to the lumber of " sawyers," or the 

 grubs of timber-beetles. 



While in the virgin spruce forest on the eastern shores of Lake Ken- 

 nebago, Maine, which had never been lumbered, my attention was 

 forcibly called to the necessity of cutting down the dead and dying 

 spruces so as to save the healthy trees. It is of course out of the question 

 to burn such dead timber, but we question whether it would not in the 

 long run pay the owners of lumber lauds to send parties in to cut down 

 the trees, remove the bark, and thus prevent the breeding of bark- 

 borers, aud hasten the decay of trees infested by timber aud bark-borers. 



Plantations aud forests of limited extent can with comparative ease 

 and slight expense be kept in neat, trim order by judicious thinning 

 aud removal of injured or infected branches, the latter being burnt. 



Borers in shade and ornamental trees. — Our experience in detecting the 

 gashes in the bark of the spruce and fir made by the female Monoham- 

 mus, the parent beetle of the "sawyer" or borer, and those made in 

 rock-maples by the female beetle of the maple-tree borer, so destructive 

 in parks and streets, has taught us that it is quite practicable during 



