1388 ARBORETUM AND FRUTICETUM. PART IIL. 
course at about right angles from the 
primary channel, on each side of it. 
(See jig. 1236.) The true food of the 
insect is the inner bark; and the 
erosion of the soft wood is so slight, 
as to be, perhaps, nearly accidental. 
The course of each individual larva, 
on each side of the primary channel, is 
about parallel to that of the larva next 
to it; and each forms a channel by its 
feeding that is enlarged as the larva 
increases in size. When each larva has 
finished its course of feeding it stops in 
its progress, turns to a pupa, and then to 
a beetle; after which it gnaws a straight 
hole through the bark, and comes out. 
The beetles begin to come out in 
about the latter end of May of the year 
following that in which the eggs were 
deposited. The sexes afterwards pair, 
and the females, bearing eggs, bore 
through the bark, as before detailed ; and so on from generation to generation, 
and year to year. 
The result of the erosions of the female parent, and of the larva, in the inner 
bark and soft wood, is that of cutting off the vital connexion between these 
two parts; and, when the erosions effected in a tree have become numerous, of 
occasioning its death, by preventing the ascent and descent of the sap. It 
has been said that the scolytus never attacks a tree in a perfectly healthy 
state; and, also, that trees suffering under carcinoma (see p. 1385.) are par- 
ticularly liable to it. In the year 1825, an avenue of elm trees in Camberwell 
Grove were attacked by this disease, which was supposed to be brought on 
by the gas which escaped from the pipes laid down along the road being 
absorbed by the roots; and which gave rise to a suit in Chancery between the 
inhabitants and the proprietors of the gas-works. Various persons, considered 
as competent judges, were employed to ascertain the cause of the decay of the 
elms ;. and their general conclusion was, that the carcinoma had been brought 
on by old age, excavations for building in an exceedingly dry soil, and an extraor- 
dinarily drysummer, and that the gas had had no influence in producing the decay 
of the trees. The trunks of the trees, when examined in 1826, were found 
infested with an immense number of larvz feeding on the soft inner bark. An 
interesting account of the Camberwell elms will be found in the Gardener’s Ma- 
gazine, vol. i. p. 378. In relation to the capability of the scolytus to effect injury 
on elm trees, it is stated that 80,000 have been found in a single tree. It 
has also been remarked that the scolyti seldom destroy the trees they attack 
the first year that they commence their ravages; and that they prefer a tree 
that they have already begun to devour, to a young and vigorous tree. 
(See the observations of Mr. Spence in p. 1589.) It is easy to ascer- 
tain the infested trees, as the bark will be found perforated by small holes, 
as if made by shot or a brad-awl, in various parts; and little particles 
of a substance like fine sawdust will be found on the rough surface of the 
bark, and at the foot of the tree. The scolyti, as Mr. Denson, sen., has 
observed, never attack dead trees. The Scdélytus destrictor, as an enemy to 
elm trees, appears first to have attracted the attention of entomologists in 
England about the year 1824, by M‘Leay’s Report to the Treasury upon 
the state of the elms in St. James’s and Hyde Parks. (See this Report in 
Edin. Phil. Journ., No. xxxi. art. 12.3; and see Tilloch’s Phil. Mag., Oct. 1823, 
art. 51.) In the year 1828, a controversy was carried on in a Cambridge 
newspaper, between Mr. John Denson, sen., the author of A Peasant’s Voice 
to Landowners, &c., and Mr. J. Deck of Cambridge, respecting the cause of 
