The ailanthus,[10] or tree of heaven, is a tall, broad, handsome tree that is especially valuable in the heart of closely built or smoky cities. The staminate and pistillate flowers are borne on separate trees. Only the pistillate trees should be used, as the odor of the blossoms of the staminate ones is very objectionable for about 10 days in late spring. These may be produced by grafting from pistillate trees or by propagating from suckers or root cuttings from such trees if they have not been grafted. The ailanthus may not succeed in regions 5 and 13.
[10] Ailanthus altissima (Mill.) Swingle (A. glandulosa Desf.).
ASH.
There are three kinds of ash trees that are useful for street planting.
The white ash[11] is a large oval-headed tree, reasonably satisfactory on rich lands in regions 1, 2, 3, 4, 9, 10, 11, and 12, but it is better adapted to suburban than urban conditions.
[11] Fraxinus americana L.
The green ash[12] is one of the few successful trees in regions 6, 7, and 8 and may succeed in region 5. It grows well throughout the remainder of the United States, but is of less value than other trees there. It is much smaller than the white ash, with a broad round top.
[12] Fraxinus lanceolata Borck.
The European ash[13] is a large, handsome, round-headed tree suited to regions 1, 2, 3, and 4.
[13] Fraxinus excelsior L.