Loudon--every inch a fine gardener, true lineal descendant of Bacon in the art of gardening--recommends in his "Arboretum" (pp. 11, 12) the heading down of large trees of common species, and the grafting upon them foreign species of the same genus, as is done in orchard fruit-trees. Hawthorn hedges, for instance, are common everywhere; why not graft some of the rare and beautiful sorts of tree thorns, and intersperse common thorns between them? There are between twenty and thirty beautiful species and varieties of thorn in our nurseries. Every gardener can graft and bud. Or why should not scarlet oak and scarlet acer be grafted on common species of these genera along the margins of woods and plantations?
In planting, the gardener has regard for character of foliage and tints, the nature of the soil, the undulations of ground and grouping, the amount of exposure. Small plantations of trees surrounded by a fence are the best expedients to form groups, says Repton, because trees planted singly seldom grow well. Good trees should not be encumbered by peddling bushes, but be treated as specimens, each having its separate mound. The mounds can be formed out of the hollowed pathways in the curves made between the groups. The dotting of trees over the ground or of specimen shrubs on a lawn is destructive of all breadth of effect. This is not to follow Nature, nor Art, for Art demands that each feature shall have relation to other features, and all to the general effect.
In planting trees the variety of height in their outline must be considered as much as the variety of their outline on plan; the prominent parts made high, the intervening bays kept low,[42] and this both in connection with the lie of the ground and the plant selected. Uniform curves, such as parts of circles or ovals, are not approved; better effects are obtained by forming long bays or recesses with forked tongues breaking forward irregularly, the turf running into the bays. Trees may serve to frame a particular view and frame a picture; and when well led up to the horizon will enhance the imaginative effect of a place: a _beyond_ in any view implies somewhere to explore.
[Footnote 42: "One deep recess, one bold prominence, has more effect than twenty little irregularities." "Every variety in the outline of a wood must be a _prominence_ or a _recess_" (Repton, p. 182).]