(67 



PLANTING AND PLANTATIONS. 



PLASTERING. 



663 



making up deficiencies, thinning, and pruning. Deficiencies seldom 

 occur if the planting be at first duly performed ; and every endeavour 

 should be used to prevent the necessity of making up. This is always 

 done with considerable disadvantage to the plants thus introduced, 

 unless the spaces be trenched ; but in that case, if the species of tree be 

 properly chosen, the plants may do well in consequence of the shelter 

 afforded by .the older surrounding individuals. 



Thinning should be commenced in due time. No branch of the 

 temporary trees should by any means overhang the top or even 

 branches of those that are permanent. The shelter on the most 

 exposed sides of the plantation should be formed of robust, vigorous, 

 growing kinds, and it should be allowed to remain unbroken. Plan- 

 tations that have been neglected till they have formed a dense thicket 

 must be thinned gradually ; for if thinned at once, those left would 

 be injured by the sudden exposure, and would be blown over by 

 winds. 



Pruning is an important operation in the management of planta- 

 tions, but it is often improperly practised for want of the knowledge 

 of a few physiological facts, which are essentially necessary to be 

 stated before any rules for pruning can be properly given. If these facts 

 be understood few rules will be required, but otherwise a volume of 

 directions are liable to be misapplied. It ought therefore to be under- 

 stood, that the sap ascends from the stem chiefly through the albur- 

 num, or outer layers of young wood. It then enters the leaves, when 

 , posed to the influence of light. Having in consequence under- 

 gone an elaboration, it descends on the outside of the alburnum, that 

 is to say, through the inner bark, the internal surface of the latter 

 possessing a great degree of lubricity, whereby the passage of a portion 

 of the juices at least is facilitated to the roots, whilst part is detained 

 and becomes organised.by the action of the medullary rays, forming a 

 new layer of woody matter. The thickness of the layer so formed is 

 very different in different species ; but in the same species, all other 

 circumstances being the same, it is in proportion to the surface of 

 leaves. The aggregate horizontal growth, or in other words the dia- 

 metrical extension of the stem, branch, and even roots, depends upon 

 the quantity of healthy foliage. The diametrical increase of any par- 

 ticular part corresponds with the greater or less proportion of foliage 

 above that part. Again, it may be stated that if any one tree has a 

 clear stem of 20 feet in length, and another has one of 40 feet, the 

 roots and foliage of both being equal, the layer of new wood will be 

 much thinner in the latter case than in the former ; for the deposition 

 of woody matter will have to extend over double the surface in the 

 tall tree. It may be also remarked, that, in general, if a tree be left 

 entirely to nature, it will ultimately produce a greater bulk of wood, 

 taking stems and branches together, than would be the case if sub- 

 jected to pruning. Except however in the case of growing for fuel, 

 pruning is more or less necessary. The value of a timber-tree dej>fiid.s 

 chiefly on the stem, the branch timber being of less value. The object 

 to be kept in view in pruning for timber is the production of a clean 

 stem with as small a proportion of branches as possible. But it has 

 been explained that the growth of the stem depends on the quantity of 

 foliage, and without branches a sufficient quantity of foliage cannot be 

 maintained. Whilst, on the one hand, an undue preponderance of 

 branches is prevented by pruning, yet, on the other, as much foliage 

 should be preserved as circumstances will permit. 



An excessive privation of foliage should never be occasioned at any 

 one time. It is therefore advisable that pruning should be commenced 

 early, in order, as it were, to repress irregularities in the bud. At all 

 events, whenever an irregularity can be clearly distinguished as such, 

 it should be checked. Thus, when a shoot, occupying the position of 

 a branch, ascends in competition with the top, or leading shoot, and is 

 allowed to go on for years, the stem will have a forked character; or if 

 the competing portion be amputated after it has acquired a large size, 

 the timber will be rendered unsound. But if the shoot from which 

 this aspiring limb took its rise had been stopped in the first or second 

 season of its growth in summer, the tree might have been grown with 

 a clean regularly tapering stem. It is only great irregularities however 

 that should be meddled with during the early growth of the plant ; 

 otherwise the increase of roots is prevented, such increase being 

 reciprocal with that of the branches. 



Young shoots of the above description may be checked by being 

 shortened in summer ; but no large branches should be cut off at that 

 season, nor after the sap begins to. flow briskly in spring. Towards 

 autumn, however, when the leaves have nearly ceased to carry on their 

 functions, pruning may be very properly performed ; and some species, 

 for example the birch and maple, require to be pruned at that time, 

 otherwise they are apt to bleed. Th period at which bleeding , that is, 

 an extravasation of sap, takes place with greatest force, is immediately 

 before the bursting of the buds in spring. If a branch be cutoff when 

 in foliage, the remaining portion draws the sap and prevents effusion at 

 the wound. Some derangement will of course be produced in the flow 

 of sap ; and a diminution of the process of lignifiavtion and of the 

 formation of roots will be occasioned, owing to the abstraction of a 

 certain extent of foliage. But when the sap is in motion, and the 

 leaves at the same time not expanded, the amputation of a branch is 

 followed by a flow of sap, which appears to drain from every part of 

 the tree. The sap becomes stale on exposure to the air ; it then affects 

 the cambium and inner bark, often to a considerable extent below the 



wound, and if these are not in all cases so far completely killed, yet 

 they are generally more or less injured, and canker is apt to ensue. 



Supposing it were required to rear a tree so as to have a stem of 

 clean-grown timber, as tall and as thick as could possibly be obtained 

 in any given time. The first consideration is the root, the plant being 

 supposed to be young, with a top or upright leading shoot, and several 

 side branches. All these should be left undisturbed in the first 

 instance, unless such of the latter as may require a check if growing 

 too strong for the others or for the leader. The laterals should be left, 

 for the sake of the roots, till their presence on the stem becomes incon- 

 sistent with the object of producing it as free as possible from knots, 

 taking also into consideration that the difficulty in healing the wound 

 increases as the branches get older. A few of the largest shoots should 

 be those first removed. They may be shortened in the first instance 

 after midsummer, and afterwards cut off smoothly by the lowest 

 circular wrinkles which form round their base, close to the stem, but 

 without slicing off a portion of the bark ; a slovenly practice, of which 

 only bad pruners are guilty, and which can only have the effect of 

 diminishing the power of the bark to close over the wound neces- 

 sarily made by the pruning-knife. Such unnecessary wounds cause an 

 extravasation of sap, as may be seen especially in coniferous trees, 

 where they are generally covered with resinous exudations. In the 

 following season the next largest branches should be in like manner 

 displaced, care being still taken, on account of the importance of the 

 foliage, as already explained, that the quantity removed shall be no 

 more titan is absolutely necessary. 



Small branches along the stem should be left till they approach the 

 dimensions by which the removal of the others is regulated. These 

 principles should be followed up till the required height of stem is 

 attained ; after which the branches composing the top shall be allowed 

 full freedom, in order to increase, by their organising power, the dia- 

 meter of the stem. 



Coniferous trees require little pruning ; nor is it necessary to com- 

 mence so early with them as in the case of other kinds. In dense 

 forests they are found with straight stems approaching the height of 

 100 feet clear of side branches, the latter gradually decaying below as 

 they become excluded from light and moisture by those above them. 

 When from this cause the lower branches of coniferous trees are 

 observed to lose in a great measure their vigour, and when their foliage 

 contributes little to the enlargement of the stem, they may then be 

 very properly cut off, without waiting for their actual decay. It is a 

 question whether the branches of these trees should be cut close to 

 the stem at once, in pruning; or whether they should first be iiiagged, 

 that is, cut at some distance from the stem, and either allowed so to 

 remain or be afterwards cut close. That plan is best to adopt by 

 which the least exudation of resinous substance is occasioned, and the 

 blemish soonest overgrown. With the view of preventing the former, 

 the branch may be shortened only to the first live twigs, so as almost 

 to nullify its connection with the stem, preparatory to its final and 

 close removal in the following season. 



By choosing the proper season, and by .previous shortening, large 

 limbs of any healthy tree may be closely amputated so as to heal over 

 without affecting the tree generally, or even the portion of stem more 

 immediately connected with the limb to any material extent ; yet the 

 new layer of wood will prove, on cutting up the timber, to be only in 

 close contact with the surface of the wound, which will remain dead, 

 and with which the living matter enclosing it could uot coalesce. A 

 piece of unsound wood is thus embodied. In this case it would be 

 advisable to shorten the limb to such of its laterals as will just be 

 sufficient to keep it alive till the tree is felled. If, in the interval, the 

 branch should push vigorously, means must be adopted to keep it 

 always in a reduced state, by merely allowing as much foliage as will 

 keep the branch alive, without affording any material addition to its 

 diameter. 



The proper season for felling trees is when the sap is most at rest. 

 The operation ought not to be performed at any other time, unless for 

 fire-wood. The quantity of sap that may be drawn from some trees is 

 very great. This sap contains the elements of fermentation, the 

 powerful effects of which are evident even on the strong fibre of the 

 oak. Softer woods, although very tough if cut at the proper season, 

 have been observed to crumble almost to powder in a year or two, in 

 consequence of having been cut when in sap. 



(Sang's Planter's Jfalendar ; London's Arboretum Britannicum ; 

 i'nrycl'ipcedia of (Hardening ; Morton's Cyclopedia of Agriculture ; Ste- 

 phens' Book of the Farm.) 



PLASTER OF PARIS. [CALCIUM ; Sulphuric Acid and Lime.] 



PLASTERING. The application of any coat of plastic material to 

 the uneven surfaces of masonry or of wood-work, for the purpose of 

 bringing the latter to a sufficiently smooth surface to receive elaborate 

 surface decoration, is known by the generic name of plastering ; but in 

 practice a distinction is made in order to separate the more elaborate 

 processes of the plasterer's art, which are known by the names of 

 stuccos, scagliolas, Ac. 



Ordinary plastering is either executed with the pure dehydrised 

 sulphate of lime (or the baked gypsum), or with mortars composed of 

 the carbonates of lime, forming a substratum to receive ultimately a 

 finishing coat of fine plaster ; the choice between those materials being 

 decided by motives of economy, for the gypsum does not occur in. 



