REMEDIES AGAINST FOREST INSECTS. 27 
less sharply distinguished ; and it is only in the oaks, ashes, and elms, 
where the pores are arranged in rings ("ringporeu") that the richly 
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. #., Agaricus melleus, Aecidiumpini, Peziza Willkommii. All in- 
sects which externally gua w the bark or the wood of coniferous trees, e. g„ 
bark borers, wood wasps, Grapholitha pactolana and G.coniferana, Bioryc- 
tria abietella; different weevils (Hylobius and Pissodes), produce a more 
or less strong flow of pitch or resin. But also in the interior of the 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 lands to send parties in to cut down 
the trees, remove the bark, and thus prevent the breeding of bark- 
borers, and hasten the decay of trees infested by timber and bark-borers. 
Plantations and forests of limited extent can with comparative ease 
and slight expense be kept in neat, trim order by judicious thinning 
and 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, aud those made in 
rock -maples by the female beetle of the maple-tree borer, so destructive 
in parks aud streets, has taught us that it is quite practicable during 
