The climatic conditions of the site are intermediate between those of the northern, the southern, the eastern and the western parts of that region of the United States which extends from the Atlantic to the Great Plains. During the Spring and early summer there are more frequent and copious falls of rain [986]than occur throughout the region on an average and the winters are probably slightly colder than the average. Occasionally, at intervals it may be of twenty years, the mercury falls much below its lowest depression, in ordinary winters, and few trees survive that are not hardy in the greater part of the region.

The rate of yearly growth and the maximum size of most of the trees which grow naturally upon the site, does not vary greatly from the average of the same species, as they are found growing in the eastern half of the United States. The soil of the site is of less than the average fertility but perhaps, generally, of a little more than the average depth. It is mainly a clayey loam, with a porous sub-soil.

Considering the somewhat rugged topography of much of it, the site is of a similar character which, in Europe, are as a rule, thought to be more profitably devoted to forestry rather than to agriculture. There are few, if any, other places in the eastern half of the continent, in which a larger range of woody plants grow naturally. Among them, there are some that are indigenous to the southern parts of the region and not to the northern; others, which grow naturally in the northern and not in the southern parts of it.

Having regard to all these circumstances, it is considered that the site is not an unsuitable one in which to establish a collection of such trees and other woody plants as may be hoped to be successful and desirable, under the conditions above defined, for use in the eastern half of the continent.

It is proposed to plan this arboretum more particularly as a field for studying the value of extensive plantings, made with reference to the management of economic forests and the composition of scenery, and the difference is to be observed between the two objects thus set forth, and those commonly had in view in the planting of orchards, gardens, dooryards, graveyards and other places not admitting of treatment with a view to such softening and blending of forms and tints, as a result of gradations through distance.

With a view to the things thus stated, a main arboretum road is to be laid out in such a manner that the ground bordering upon it will be of considerable variety with respect to situation exposure and soil, and as far as practicable, consistently with a predominating regard for the main purpose above stated, it is to be made a pleasant route to be followed by those having no purpose of study. To this end, presentation of agreeable prospects at a distance is to be had in view, as well as the presentation of interesting objects of the immediate borders of the road. Beginning near the entrance to this road, trees and lesser woody plants are to be set agrowing on its borders, families and genera following each other mainly in the order adopted in Bentham and Hooker’s Genera Plantarum, and which is known as the natural order. But variations from this order may be occasionally made, if by such variations, plants of a particular genus or series of genera can be placed under conditions better adapted to their health and development, and to the better exhibition of their respective distinct characteristics.

It is intended to include in the arboretum specimens of every species, [987]and of such varieties as are adapted to the purpose stated, which are now in cultivation and which may be distinguished by peculiarities in growth, foliage, flowers and fruit. In general, varieties will be admitted to the arboretum road having special qualities by which the character of passages of scenery will be affected for a considerable period, and not, for example, merely for the brief flowering season. That those seeking information that will be useful in the designing of plantations for scenery, or in the planting of economic forests, may find what is required for their purposes within reasonable limits of space, varieties of plants will be excluded from the arboretum road that are chiefly interesting because of strikingly abnormal qualities not recommending them to be used, either as elements of pleasing landscape composition or with a view to commercial profit in economic forestry; also such varieties as are only distinguishable from others of the same species by peculiarities of their flowers or their fruits, and which have no other qualities that are notable because of their effect in the composition of scenery. If any such varieties were included, it would be for the purpose of illustrating distinct types in variations of this character. A special place may be provided apart from that of the main Arboretum for a collection of varieties, which, because phenomenal in these or other respects, are more interesting as curiosities than as objects of instruction, with regard to scenery or to forestry.

Not less than four specimens are to be planted near the road of each species and variety of trees to be exhibited. A part of the specimens planted will be removed before they come to crowd one another, leaving two or more of those which promise to best represent the character of the trees, and they are to be given sufficient room for the branches to spread at least on two opposite sides to the greatest distance that they would be likely to spread if wholly unimpeded. At a suitable distance behind such spreading specimen trees, others of the same species are to be planted, with a view to the exhibition of their character when grown in groups. At a suitable distance beyond these groups would be the natural forest, or the forest acres referred to hereafter, and these would be faced with trees of the kinds represented by the individual trees and groups to show their effect in combination with other trees in mass.

In order to study the habit, character, rate and economic value of the growth of trees under different conditions in a forest, it is the purpose to provide near the facilities, in which there are trees, areas of several acres extent on which there may be planted an acre each of such trees as are deemed worthy of trial either by themselves or in mixture with other trees. While it is not deemed essential that such forest acres shall be immediately adjacent to the corresponding tree in the Arboretum road, it is the intention to have them so arranged that a student will not be compelled to go much out of his way to study a tree under all the conditions in which it will be placed.

The ground above and between the trees of the Arboretum is to be generally planted with the collection of bushes, vines and creepers, and, as far as practicable, consistently with its two leading purposes, such shrubs are to be [988]displayed before and between the trees, of the same genus that they are associated in the natural order. In placing these shrubs, the purpose is to be kept in view to have them eventually illustrate the value of shrubs of each species: first, when standing singly or as specimens; second, when clustered in groups; third, when in mass, standing in open ground; fourth, when growing as underwood. Finally, as with trees so with shrubs, considerable elasticity must be allowed in all the rules, the interest of those seeking pleasure from scenery being consulted as far as may be, without putting students to serious inconvenience.

To avoid the excessive care and expense that would otherwise be necessary, it is not intended to introduce paths or to keep turf spaces open that will serve as paths, but to provide a ground cover of low shrubs or covering plants, which will not be injured if occasionally trodden upon, over which students may without inconvenience pass and come nearer to the specimens than they would be able to come if following the road. The material used for this purpose will not necessarily be of the same genus as that of the collection with which they are used.

If economy of space or the convenience of students is to be observed by it, shrubs of a particular genus may be taken out of the places which they would have if the natural order were to be strictly followed, and be sent before, among or a little in advance of the trees near which they would be placed if the natural order were strictly followed. In this respect it is to be provided simply, that when a student coming to one species of the genus, wishes to examine another species of the same genus, he may expect to find it near by. The same will be true with reference to the forest acres.

When a specially promising, young, vigorous tree or bush of any kind is found growing naturally on the Arboretum or any of its branches, it is not necessarily to be removed in order to secure an adherence to the rule of pursuing the natural order. In such a case, consideration is to be given to its value, as an element of scenery rather than as an object of instruction.