In compliance with your request, we have examined Commonwealth Avenue with the view of recommending a scheme for re-planting the central greens.

It is a well established rule in urban planting that only trees of one variety can be used in the same continuous street. If this rule is disregarded, and trees differing widely in habit, rate of growth, and in the period of putting on or losing their leaves, are planted side by side, incongruous and disagreeable effects will result; and such disagreeable effects will increase rather than diminish as the trees approach maturity and assume the widely different characters peculiar to different species. The advantage of using one instead of several varieties of trees in the same street or avenue will be readily seen by comparing the Beacon Street Mall below Joy Street, or the Charles Street Mall, with the plantation in the older portions of Commonwealth Avenue.

In order to obtain in Commonwealth Avenue the uniformity which seems to us so essential to the future beauty and dignity of the finest street in the city, we recommend that it be entirely re-planted from Arlington Street to West Chester Park; and that, instead of the double row of trees now used, a single row be planted on each side of the central walk, ten feet from the line of the street.

We recommend that European elms, of one variety and of a standard size, should be used for this purpose. This selection is based on the fact that the European elm has been thoroughly tested in Boston and its immediate vicinity during a period extending over more than a hundred years,—a period long enough to show its entire adaptability to our climate; and because the largest and finest trees which have ever been planted in Boston have belonged to this species, which in this climate seems better fitted than any native tree of a similar class to withstand the droughts, heat and dust, to which all city trees are necessarily subjected.

We recommend a single rather than the double row of trees now used, and that the trees should stand at least forty feet apart in the rows, in order that in the future they may attain a development worthy of the wide and stately thoroughfare which is to join the Common and Public Garden with the new system of city and suburban parks.

If Commonwealth Avenue is re-planted in accordance with these suggestions, it will not be necessary to remove at once the trees now growing in the older portions of the street, or at least many of them. The new plantation [516] can be made by inserting the new trees between existing ones; and these can be gradually removed as they encroach on the young plantation.

We find that the total length of the eight grass plots between Arlington Street and West Chester Park is 4100 feet, and that to plant it in the manner proposed will require 180 trees, namely:—

24	between Arlington and Berkeley Streets.
22	between Berkeley and Clarendon Streets.
24	between Clarendon and Dartmouth Streets.
24	between Dartmouth and Exeter Streets.
26	between Exeter and Fairfield Streets.
22	between Fairfield and Gloucester Streets.
16	between Gloucester and Hereford Streets.
22	between Hereford and Chester Park.
Total, 180

Suitable trees for this purpose can be imported from England at a cost which, including freight, duties, etc., should not exceed $1.00 each.

It is needless to remind you that the soil of Commonwealth Avenue plots (a few inches of loam overlaying loose, porous gravel) is entirely unsuited to grow large and long-lived trees. In order to produce a lasting and satisfactory result, it will be wise to make a considerable outlay in preparing the ground for the new plantations. We recommend that pits at least ten feet square and four feet deep should be made for each tree, and that the soil excavated should be entirely replaced by the best virgin loam procurable. Even larger pits are desirable; for, the existing soil being unfit to support plant-life for any length of time, the size and age to which any trees planted there will be able to attain must depend on the amount of artificially prepared nourishment which can be supplied to them.

If Commonwealth Avenue is to be re-planted next spring, it is desirable, should the weather permit, to have the ground prepared this winter, that the new loam in the pits may have time to become properly settled and compacted before the trees are planted. The order for the trees, too, should be sent to England at once, as it may take some time to pick up there a sufficient number of suitable size and shape. Even if it should be found impracticable to plant next spring, it might be desirable to send for the trees now and grow them on the Austin Farm until needed for Commonwealth Avenue, and in this way gain the advantage of their larger size.