As the trees and shrubs in the belt are much thicker than those in the collection, they will have to be thinned out from time to time; in doing which, the weakest and least valuable plants must be removed first, so that the belt may never have a crowded appearance, or choke up the roses, and at the same time be sufficiently filled with evergreens to conceal, in a great measure, the boundary hedge from the walk. Many of the trees in this belt, and also a number of the old trees of common sorts left standing in the flower-garden and in the collection, will have to be removed in the course of a few years, otherwise the effect of the whole, as well as the growth of all the more delicate kinds now planted, will be materially injured. In a word, it forms no part of the design of this Arboretum to exhibit large trees, more especially of the common kinds; and whenever any one of these, or, indeed, any tree whatever in the Arboretum, reaches a greater height than 40 or 50 feet, it should be removed. That height is quite sufficient for producing shade, and for showing the form and character of the tree, and its flowers and fruit; and nothing more is required, or can be admitted in an arboretum on so limited a piece of ground. If this part of the management laid down be neglected, the rapid-growing large trees will soon overtop the slow-growing smaller ones and the shrubs, and ultimately destroy all the finer kinds. As several of the trees and shrubs forming the collection are small plants of kinds recently raised from seed in the Horticultural Society's Garden, and just introduced into the country, it is not improbable that they may, in some cases, be wrongly named; but, if I am permitted, I shall be happy to examine, free of expense, all the plants, at intervals of two or three years, and correct the nomenclature, when necessary, during my life; because much of the usefulness of this Arboretum will depend on the nomenclature being correct. As new species of trees and shrubs from foreign countries are continually increasing the collections in British gardens, when any of these are to be added to the Derby Arboretum, it can only be done with propriety and success by taking up the whole and replanting, adjusting the distances to the estimated heights to which the plants will grow in the given climate and soil. It will be better, therefore, to make no additions whatever for the next 15 or 20 years, and then to take the whole up and replant, introducing the new kinds in their proper places.
