P. deltoidea, Marsh.
The cottonwood justifies its existence, if ever a tree did. On our Western plains, where the watercourses are sluggish and few and often run dry in midsummer, few trees grow; and the settler and traveler is grateful for the cottonwoods. The pioneer on the Western prairie planted it for shade and for wind-breaks about his first home. Many of these trees attain great age and in protected situations are magnificent though unsymmetrical trees, shaking out each spring a new head of bright green, glossy foliage, each leaf responsive to the lightest breeze.
"Necklace-bearing poplar," it has been called, from the fact that children find pleasure in stringing for beads the green, half-grown pods containing the minute seeds. They also delight in gathering the long, red caterpillar-like catkins of the staminate flowers, the pollen bearers, from the sterile trees. A fertile tree is sometimes counted a nuisance in a dooryard because its pods set free a great mass of cotton that collects in window screens, to the annoyance of housewives. But this seed time is soon over.
Just these merits of quick growth, prettiness, and tenacity of life, belong to the Carolina Poplar, a variety of native cottonwood that lines the streets of the typical suburban tract opened near any American city. The leaves are large and shine with a varnish which protects them from dust and smoke. But the wind breaks the branches, destroys the symmetry of the tree's head, and in a few years the suburban community takes on a cheap and ugly look. The wise promoter will alternate slow-growing maples and elms with the poplars so that these permanent trees will be ready to take their places in a few years.
The Aspen
P. tremuloides, Michx.
The trembling aspen, or quaking asp, is the prettiest tree of all the poplar tribe. Its bark is gray and smooth, often greenish and nearly white. An aspen copse is one of the loveliest things in the spring landscape. In March the bare, angular limbs show green under their bark, one of the first prophecies of spring; then the buds cast their brown scales and fuzzy gray catkins are revealed. There are few shades of olive and rose, few textures of silk and velvet that are not duplicated as the catkins lengthen and dance like chenille fringe from every twig. With the flowers, the new leaves open; each blade limp, silky, as it unrolls, more like the finest white flannel than anything else. (See illustrations, [pages 86-87].) Soon the leaves shed all of this hairy, protective coat, passing through various tones of pink and silver on their way to their lustrous, bright green maturity. Their stems are flattened in a plane at right angles with the blade. Being long and pliant besides, they catch the breeze on blade or stem, and so the foliage is never still on the quietest of summer days. "Popple" leaves twinkle and dance and catch the sunlight like ripples on the surface of a stream, while the foliage of oaks and other trees near by may be practically motionless.
The Balsam Poplar
P. balsamifera, Linn.
The balsam poplar is the balm of Gilead of the early settlers, the Tacamahac of the Northern Indians. They squeezed the fragrant wax from the winter buds and used it to seal up the seams in their birch-bark canoes. The bees taught the Indian the uses of this glutinous secretion, which the tree used to seal the bud-scales and thus keep out water. When growth starts with the stirring of the sap, this wax softens; then the bees collect and store it against a day of need. Whether their homes be hollow trees or patent hives, weather-cracks are carefully sealed up with this waterproof gum, which the bee-keeper knows as "propolis."