PLANTING. 73 



The larva of the laziocampa quercus sometimes strip the leaves entirely 

 of the branches of the oak. When the trees are young, and the attack 

 is perceived before it has made great progress, the application of caustic 

 lime water, served by the hand-engine before mentioned, is the only 

 topical application we have found practicable, as regards cost, time, and 

 effectiveness. 



The different species of coccus or scale-like insects which infest most 

 trees, seldom attain to such numbers as to endanger seriously the health 

 of forest-trees. 



The aphis or fly is more common and injurious. Almost every distinct 

 species of tree has a species of aphis peculiar to itself. The glutinous 

 substance which, in hot arid weather, appears so general on the upper 

 surface of the leaves of trees, is produced by these insects. This sub- 

 stance, by attracting other insects, and by arresting smoke and dust 

 on the surface of the leaves, prevents the leaves from performing their 

 healthy functions. For large trees and extensive plantations topical 

 remedies are of course out of the question. In confined cases a solution of 

 soft soap, or of water impregnated with caustic lime and sulphur, are either 

 of them very effectual cures. 



The gall fly (cynips quercus folii) deposits its eggs in the membrane 

 of the leaves of the oak, and produces those tumours on the leaves called 

 oak galls. The extent of injury inflicted on the general health of the tree 

 has never been observed to be great, or such as to warrant any expensive 

 trial for a cure. 



The last disease, or rather defect, that may be mentioned here, is 

 termed shake, and should be carefully guarded against in the culture of 

 forest-trees. Trees, though outwardly to all appearance sound in the 

 stem, are often found with splits of 'several feet in height from the root 

 upwards. This is frequently caused by strongly bending the stem of a 

 tree from the top when young. The stem of trees in plantations which 

 have been neglected in judicious thinning and pruning, being tall and 

 slender in proportion to the branches of the top, these act as a lever to 

 the wind, and in time produce this blemish in the timber. In carrying out 



although in smaller rmmber. Before the bark began to peel off, gas pipes had been laid 

 near the foot of one row of the elms, the time had been only about six weeks, and the 

 mischief was imputed to the escape of the gas among the roots. This reason, however, 

 was untenable, inasmuch as trees removed to a considerable distance from the gas pipes 

 were equally affected; while a few already mentioned adjoining it escaped. Besides, the 

 foliage shewed no signs of being affected, which all gaseous poisons have the imme- 

 diate effect of shewing first on the leaves. In this instance the state of the trees, previous 

 to the introduction of the gas pipes near to the roots, showed that the scolytus destructor 

 had been one of the several causes that produced the death of the trees. These elms were in 

 rows, and formed an avenue. They had been planted too close in the rows, and had also 

 been neglected in thinning and pruning. The remains of dead stumps, and the numerous 

 cavities left by others, marked out by the discoloured traces on the bark of the long 

 existence of an yearly haemorrhage of sap, and also the scanty tops in proportion to the 

 size of the stems, all proved that the disease tabes had been confirmed. Add to this the 

 bad effects of drains, and deep foundations cut out in the immediate neighbourhood of the 

 trees, accompanied by two excessively dry seasons (1825 and 1826) so favourable for the 

 propagation of the scolytus destructor, and the crisis and results of the disease will not be 

 any subject of wonder. A tree of the pinus pinaster, which had been reared in a pot, was 

 subjected to the influence of gas the same as that supplied to the roots of the elm, but without 

 producing any perceptible effect. A large ox bladder was filled by the writer of this with 

 the carburetted hydrogen gas, and connected by a pipe with the draining aperture of the 

 pot, in which the roots of the pine were confined. This quantity of gas was made to pass 

 through the earth in the pot during the space of forty-eight hours, and renewed and 

 continued for three weeks ; but, as just now observed, without producing any ill effects on 

 the health of the plant. The pine is liable to be injured and destroyed by the insects 

 before mentioned, in the same manner as the elm. 



