This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Several kinds of Poplar are largely grown, being used as windbreaks, screens, etc. They flourish in almost any soil, but prefer damp situations. The most common kinds in commerce are as follows: P. alba, the Abele or White Poplar, 100 ft., has silvery-white leaves. The variety Bolleana resembles a Lombardy Poplar in habit; and nivea has leaves conspicuously white on the under surface. The Balsam Poplar (P. balsamifera) of North America is a fine tree with yellowish-green young leaves. There are several varieties of it, including the Ontario Poplar (candicans or ontariensis). The Lombardy Poplar (fastigiata or pyramidalis) is well known for its columnar or pyramidal habit. It is really a variety of the quick-growing Black Italian Poplar (P. nigra). The Aspen (P. tremula) is a fine British tree with a graceful drooping variety, pendula. The commoner kinds of Poplar are raised from seeds, but special varieties are usually grafted.