The generic name, _Populus_, is supposed to have come from the Latin _arbor populi_ (the tree of the people), because rows of this tree were always planted in public places about Rome. The specific name, _tremuloides_, refers to the leaves which tremble continually on account of their long, flattened, pliable leafstalks. The aspen grows wild throughout the Northern United States and in the mountains of Lower California and Mexico. [Sidenote: Large-toothed Aspen _Populus grandidentata_] _A large tree, 60 to 80 feet high, with smooth greenish gray bark. The buds are conical with somewhat downy scales and spread at right angles from the stem. Slender twigs and alternate leaf-scars._ This tree is quite distinct from the American aspen, although it is often confounded with it. It is found much less frequently than the American aspen. The wood is close-grained, soft, and light, and is used for making wood pulp and wooden ware. In old times when it was the fashion for women to wear high-heeled shoes this wood was used in making heels, as it was light and best adapted to the purpose. The specific name, _grandidentata_ (large toothed), refers to the serrations of the leaf, which are much coarser than those of the American aspen. [Sidenote: Balm of Gilead; Balsam Poplar _Populus balsamifera_] _A tall tree, 40 to 70 feet high. The bark ts smooth and greenish gray, often roughly ridged at the base of the trunk. Large buds with overlapping scales covered with a sticky, yellow, glutinous substance. Conspicuous alternate leaf-scars._ In the early spring, when the sun has melted the gummy resin which covers the buds of the balm of Gilead, one can tell the tree blind-folded by its sweet, pungent perfume, and even in winter the buds have this same strong, medicinal, aromatic odor which serves as a means of recognizing the tree. Pallas says that when grouse and other birds of that family feed on the buds of the balm of Gilead during the winter, their flesh becomes imbued with the balsam flavor, which he seems to think adds to the relish of the meat as food. This tree grows very fast on almost any kind of soil, and its roots extend to a great distance. Emerson found a balm of Gilead the roots of which had passed under a house forty feet wide and thrown up suckers on the other side. The wood, like that of other poplars, is soft and light and is used in making paper pulp, pails, and boxes. The specific name refers to the balsam on the buds. The balm of Gilead is found in the Western and Eastern States. [Sidenote: Cottonwood; Necklace or Carolina Poplar _Populus deltoides_] _A large tree, 80 to 100 feet high. The bark is dark gray and more broken in fissures than that of other poplars. The buds are glossy and resinous, but have less balsam than those of the other species. Alternate leaf-scars. Conspicuous five-angled pith in the small stems._