238t ARBORETUM AND FRUTICETUM, PART III. 



larch is never broken by snow; and very seldom torn up by winds, and then 

 only in single trees." (Gen. Hep., &c., vol. iv. p. 500.) 



I)iseases. The larch De CandoUe considers as the alpine tree which is 

 less liable to disease than any other. " There is," he says, " a peculiarity 

 which 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 Z>ermestes (Hylurgus), wliich 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 the 

 Vallais, in July, lS-20, all the trees, from the Valley of Conches to the bottom 

 of that of Ferset, bereft of their leaves through the same cause ; but none of 

 these trees perished. Sometimes, also, we see the larches having a wound of 

 resinous cancer ; but this seems to proceed from some accidental cause, such 

 as 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 diseases 

 which attack the British larches," De CandoUe continues, " must be sought for 

 in some difference existing in the physical nature or in the culture of your 

 trees 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 over 

 damp state of the latter, appear to me permanent causes which, in your 

 climate, must predispose the larches to a state of watery pletliora, which is 

 probably the cause of the destruction remarked in the heart of the wood. 

 This cause has little or no effect during the i/outk of the tree, because then 

 its vegetation is vigorous ; but it goes on increasing until the tree arrives at 

 the age when, in all trees, vegetation begins to be feebler." 



The Larch Blight (Coccus laricis). This insect, according to Sang, was 

 first observed by him on the larch, at Raith, in Fifeshire, about 1785 ; but did 

 not appear to have done any great injury to the trees. The Duke of Athol saw 

 it first on his trees in 1795, many of which, growing in low situations, it de- 

 stroyed ; winch was also the case, the Duke of Portland informs us (Quart. 

 Journ. of Agri., vol. iv. p. 548.), in low damp situations in the neighbourhood of 

 Well beck, in js^ottinghamshire. 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 coming 

 into leaf, were supposed by the duke to have " produced the blight." His 

 Grace did not find trees above 25 ft. or 30 ft. in height affected by it ; neither 

 did it appear at all on the high grounds, where a slight breeze of air could 

 shake the trees. {Gen. Rep., iv. p. 500.) According to Mr. Webster (40 

 years gardener at Munches), the trees aflected with this blight appear to have 

 their foliage covered over with a whitish substance, which adheres to the fingers 

 when touched, and consists of small globules. When the trees infested shed 

 their leaves, they appear covered with blackish stains, both on the trunk 

 and branches, and especially on the side most washed by the rains; and this 

 blackness is so conspicuous, that Mr. Webster says he could always point 

 out, in winter, the trees that had had their leaves infested the preceding sum- 

 mer. (See (iiMr- Jour. Agri., vol. v. p. 536.) Pontey judiciously observes that 

 the insect is always most abundant upon trees which have been previously in 

 an unhealthy state ; and that, in elevated situations, it is comparatively rare. 

 Both he and Sang agree that the multiplication of the insect depends greatly 

 on the languor or vigour of the tree ; and, as these are nuich atlected by the 

 seasons, two or three fine sununers and severe winters, in succession, generally 

 so reduce the numbers of the insect, as to render the injuries it commits of no 

 account. These insects appear to have been most abundant from 1802 to 

 l&OG; but have since gradually disappeared ; and, from 1815 to 1837, have 

 scarcelv been noticed as injurious i)y planters. The coccus, however, is an 

 insect which is found on various trees, indigenous and exotic ; and, as it can 

 never be wholly eradicated from tiie country, it may be expected to make 

 occasional reappearances. In the Duke of Devonshire's plantations, made in 

 1816, at Low Plains, near Penrith, the roots of the lard), wherever it was 



