In street planting the trees should be placed with reference to the room they will need when telly grown, rather than with reference to the lot boundaries; otherwise, there will be irregularity, overcrowding and unoccupied spaces. The average city lot is too narrow to permit a tree on each, and so the proper spacing on a block-must be determined irrespective of the wishes of the property owners, each of whom might want a tree in front of his house. If a block is fully planted, the trees on one side of the street should stand opposite the spaces on the other side. Planting at half distance, with the intention of removing every other tree in time, is sometimes done in order to obtain more shade at the start. Hut this plan is an objectionable one; the intermediate trees are seldom removed, and, in their crowded condition, become ill-shaped and undersized. The arrangement is a doubtful expedient, even if the superfluous ones are removed at the proper time; for while the trees are small they afford neither beauty nor shade, no matter how closely they were planted, the only case in which intervals might be filled with advantage is in a row of old trees that have passed maturity and are Hearing their end. In such a case time can be saved by planting young ones in the spaces; for when the old decaying trees fall the young ones will be well along toward replacing them. On residential streets where the houses stand well back from the fence line, with lawns or wide yards in front, the trees should not be placed at the curb, but inside the walk where they will be free from injury, obtain more moisture, and afford an equally good shade.
An avenue should be planted throughout its entire length with the same species or, at least, for several blocks. By using one kind on a street a stately architectural effect is obtained that will always be pleasing and impressive. While variety may be desirable for its educational tendency, it should not be permitted because of the irregular, unsightly appearance caused by trees of different sizes and shapes. Lamp posts, as well as trees, are deemed ornamental by many people; but no one would even think of erecting posts of different heights, size and appearance on the same street. The advantages of a variety are better secured by planting different species on different streets. A pleasing and advisable variation of this rule has been suggested by Mr. Lewis Collins, Secretary of the Brooklyn Tree-Planting Society that at the intersection of wide streets an Elm should be placed at each corner, an arrangement which would add rather than detract from the architectural appearance. A change of trees may be allowed on rural driveways where the irregularity of the scenery will better permit such an arrangement; but, even then, it is better to avoid abrupt, repeated changes by planting the same species for a considerable distance.
Although every residential street should be well shaded, an exception maybe made in commercial thoroughfares. The latter, in some instances, might be planted and thus rendered more attractive without interfering with business operations. In European cities the commercial streets often present a pleasing picture on account of the foliage which also hides from view the marks of trade, while in Holland the wharves in some places are shaded by tall trees that mingle their branches and leaves with the yard arms and rigging of vessels unloading at the docks close by.