2384

ARBORETUM AND FRUTICETUM.

I’AIIT III.

larch is never broken by snow; and very seldom torn up by winds, and thenonly in single trees.” {Gen. Rep., &e., vol. iv. p. 500.)

(Diseases. The larch De Candolle considers as the alpine tree which is ,less liable to disease than any other. “ There is,” he says, “ a peculiaritywhich all persons accustomed to observe these trees have been struck with;namely, that the trunks are remarkably healthy. They are, in particular,rarely attacked by the Dermdstes ( Hylurgus), which is so formidable to pines.Sometimes, but very seldom, we see a small caterpillar devouring the leaves,but no damage results from it. M. De Charpentier has even seen, in theVallais , in July, 1820, all the trees, from the Valley of Conches to the bottomof that of Ferset, bereft of their leaves through the same cause ; but none ofthese trees perished. Sometimes, also, we see the larches haying a wound ofresinous cancer ; but this seems to proceed from some accidental cause, suchas a blow or knock, which the tree may have received when it was in full sap.All these observations incline me to think that the cause of the diseaseswhich attack the British larches,” De Candolle continues, “ must be sought forin some difference existing in the physical nature or in the culture of yourtrees and ours. The want of a sufficiently intense light, owing to the ob-liquity of the solar rays, and to the opacity of the atmosphere, and the overdamp state of the latter, appear to me permanent causes which, in yourclimate, must predispose the larches to a state of watery plethora, which isprobably the cause of the destruction remarked in the heart of the wood.This cause has little or no effect during the youth of the tree, because thenits vegetation is vigorous; but it goes on increasing until the tree arrives atthe age when, in all trees, vegetation begins to be feebler.”

The Larch Blight (Coccus Idricis). This insect, according to Sang, wasfirst observed by him on the larch, at Raith, in Fifeshire , about 1785 ; but didnot appear to have done any great injury to the trees. The Duke of Athol sawit first on his trees in 1795, many of which, growing in low situations, it de-stroyed; which was also the case, the Duke of Portland informs us (Quart.Journ. o/Agri.,v ol. iv. p. 548.), in low damp situations in the neighbourhood ofWellbeck, in Nottinghamshire . The season at which it was most prevalent,the frosts were very severe, late in the spring, and the clouds of frost-fog,which rested on the larch on calm mornings, when the trees were just cominginto leaf, were supposed by the .duke to have “ produced the blight.” HisGrace did not find trees above 25 ft. or 30 ft. in height affected by it; neitherdid it appear at all on the high grounds, where a slight breeze of air couldshake the trees. (Gen. Rep., iv. p. 500.) According to Mr. Webster (40vears gardener at Munches), the trees affected with this blight appear to havetheir foliage covered over with a whitish substance, which adheres to the Ungerswhen touched, and consists of small globules. When the trees infested shedtheir leaves, they appear covered with blackish stains, both on the trunkand branches, and especially on the side most washed by the rains; and thisblackness is so conspicuous, that Mr. Webster says he could always Jiointout, in winter, the trees that had had their leaves infested the preceding sum-mer. (See Quar. Jour. Agri., vol. v. p. 536.) Pontey judiciously observes thatthe insect is always most abundant upon trees which have been previously man unhealthy state; and that, in elevated situations, it is comparatively i' ara 'Both he and Sang agree that the multiplication of the insect depends greatlyon the languor or vigour of the tree ; and, as these are much affected by theseasons, two or three fine summers and severe winters, in succession, generallyso reduce the numbers of the insect, as to render the injuries it commits of noaccount. These insects appear to have been most abundant from 1802 to1806; but have since gradually disappeared; and, from 1815 to 1837, p aVscarcelv been noticed as injurious by planters. The coccus, however, is 3,1insect which is found on various trees, indigenous and exotic ; and, as it cannever be wholly eradicated from the country, it may be expected to dmoccasional reappearances. In the Duke of Devonshire’s plantations, made1816, at Low Plains, near Penrith , the roots of the larch, wherever it" 3